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Saturday 24 May 2014
Friday 23 May 2014
VOLTAGE CONTROLLER,
VOLTAGE CONTROLLER,
Voltage fluctuation is a common phenomenon in every part of the country. The industrial units running round the clock usually face the problem of low and high voltage. 90% of industrial load is of motors. Electric motors draw considerably high current at low & high voltage. This higher current affects the electrical motors (particularly smaller capacity motors up to 7.5 H.P.) in three ways.
Higher current produces higher losses in electrical motors which causes premature failure of winding
These higher losses of electric motors also increase the losses of cables, switches, transformers and other associated equipment
For smooth continuous operation of motors, overload relays are usually set at 20% higher setting.
Automatic Voltage Controller is the most efficient equipment used to tackle this problem. We are one of the principal Industrial Automatic Voltage Controller Suppliers in India. Servo Controlled Automatic Voltage Controller that we offer has various advantages that help in saving a lot on electricity bill.
Advantages
Reduction in Breakdown of Electrical Equipment
Energy Saving
Improvement in Power Factor
Reduction in MDI
Uniform Quality of End Product
80% Depreciation as per Income Tax Act
Payback Period
Owing to its high efficiency and associated benefits, the payback period for the cost of Servo Voltage Stabilizer is from 6-12 months depending upon the input voltage variation and number of working hours of the plant. The HIGHER the input voltage the SHORTER will be the payback period.
Description of Automatic Voltage Controller
Servo Stabilizer primarily consists of the following
Linear Type Plus/Minus type Vertical Rolling Contact type Regulator
Double Wound Buck/Boost Transformer
Electronic Control Circuit and meter panel.
The regulator and buck boost transformer are oil cooled, housed in same or separate steel tanks. Radiators, if necessary are provided for effective cooling. Their core is built from grain oriented silicon steel Laminations which keep losses to the minimum and they are wound with electrolytic grade copper to minimize the losses, vacuum impregnated and oven dried as per IS. Attention for Power Consumer Units Having L.T. Connections but Not Having Their Own Distribution Transformer and situated in Commercial / residential Areas.
It has been observed that the said power consumers usually face unbalanced input voltage problem and to overcome the same should install Automatic Voltage Controller suitable for unbalanced input voltage (individual phase control).
Voltage fluctuation is a common phenomenon in every part of the country. The industrial units running round the clock usually face the problem of low and high voltage. 90% of industrial load is of motors. Electric motors draw considerably high current at low & high voltage. This higher current affects the electrical motors (particularly smaller capacity motors up to 7.5 H.P.) in three ways.
Higher current produces higher losses in electrical motors which causes premature failure of winding
These higher losses of electric motors also increase the losses of cables, switches, transformers and other associated equipment
For smooth continuous operation of motors, overload relays are usually set at 20% higher setting.
Automatic Voltage Controller is the most efficient equipment used to tackle this problem. We are one of the principal Industrial Automatic Voltage Controller Suppliers in India. Servo Controlled Automatic Voltage Controller that we offer has various advantages that help in saving a lot on electricity bill.
Advantages
Reduction in Breakdown of Electrical Equipment
Energy Saving
Improvement in Power Factor
Reduction in MDI
Uniform Quality of End Product
80% Depreciation as per Income Tax Act
Payback Period
Owing to its high efficiency and associated benefits, the payback period for the cost of Servo Voltage Stabilizer is from 6-12 months depending upon the input voltage variation and number of working hours of the plant. The HIGHER the input voltage the SHORTER will be the payback period.
Description of Automatic Voltage Controller
Servo Stabilizer primarily consists of the following
Linear Type Plus/Minus type Vertical Rolling Contact type Regulator
Double Wound Buck/Boost Transformer
Electronic Control Circuit and meter panel.
The regulator and buck boost transformer are oil cooled, housed in same or separate steel tanks. Radiators, if necessary are provided for effective cooling. Their core is built from grain oriented silicon steel Laminations which keep losses to the minimum and they are wound with electrolytic grade copper to minimize the losses, vacuum impregnated and oven dried as per IS. Attention for Power Consumer Units Having L.T. Connections but Not Having Their Own Distribution Transformer and situated in Commercial / residential Areas.
It has been observed that the said power consumers usually face unbalanced input voltage problem and to overcome the same should install Automatic Voltage Controller suitable for unbalanced input voltage (individual phase control).
Solar Street Lighting System
Solar Street Lighting System
Home › Products › Solar Street Lighting System
We present the finest range of Solar Street Lighting System in the market. We are considered as one of the ace Street Lighting System Suppliers in Kanpur, UP. Solar Home Lighting System offered by us provides free, renewable energy in the home with every flick of a light switch. Solar lighting can aid with this by reducing reliance on fossil fuels and the electrical grid. In addition to this, it works to save the environment as well. The use of Solar Street Lighting System is a cost effective choice.
Application Areas
Street Lighting / Highway Lighting / Bridge Lighting purposes
Park Lighting & Garden Lighting purposes
Size & Quality
Octagonal/polygonal galvanized pole from 9meter to 12 meter on wind test of 180km per hour.
Home › Products › Solar Street Lighting System
We present the finest range of Solar Street Lighting System in the market. We are considered as one of the ace Street Lighting System Suppliers in Kanpur, UP. Solar Home Lighting System offered by us provides free, renewable energy in the home with every flick of a light switch. Solar lighting can aid with this by reducing reliance on fossil fuels and the electrical grid. In addition to this, it works to save the environment as well. The use of Solar Street Lighting System is a cost effective choice.
Application Areas
Street Lighting / Highway Lighting / Bridge Lighting purposes
Park Lighting & Garden Lighting purposes
Size & Quality
Octagonal/polygonal galvanized pole from 9meter to 12 meter on wind test of 180km per hour.
Wednesday 21 May 2014
ELECTRICAL GROUNDI ANDEARTHING SYSTEMS
ELECTRICAL GROUNDI ANDEARTHING SYSTEMS
Electrical grounding and earthing systems
Presentation Transcript
ELECTRICAL GROUNDING AND EARTHING SYSTEMS Presented By: T.Sidharth Sankar Achary Regd No-1021106019 7th sem. Electrical Engg.
CONTENTS INTRODUCTION. DIFFERENCE BETWEEN GROUND AND NEUTRAL. TYPES OF EARTHING SYSTEMS. TYPES OF GROUNDING. USES. CONCEPT OF VIRTUAL GROUND. MULTIPOINT GROUND. CONCLUSION. REFERENCES.
INTRODUCTION In electricity supply systems, an earthing system defines the electrical potential of the conductors relative to that of the Earths conductive surface. The choice of earthing system has implications for the safety and electromagnetic compatibility of the power supply. A protective earth (PE) connection ensures that all exposed conductive surfaces are at the same electrical potential as the surface of the Earth, to avoid the risk of electrical shock if a person touches a device in which an insulation fault has occurred. It also ensures that in the case of an insulation fault, a high fault current flows, which will trigger an over current protection device (fuse, MCB) that disconnects the power supply. A functional earth connection serves a purpose other than providing protection against electrical shock.
DIFFERENCE BETWEEN GROUND AND NEUTRAL. Ground or earth in a mains (AC power) electrical wiring system is a conductor that exists primarily to help protect against faults and which in normal operation does not carry current. Neutral is a circuit conductor that may carry current in normal operation, and which is usually connected to earth. In house wiring, it is the center tap connection of the secondary winding of the power companys transformer. In a polyphase or three-wire AC system, the neutral conductor is intended to have similar voltages to each of the other circuit conductors, and similar phase spacing. By this definition, a circuit must have at least three wires for one to serve as a neutral. In the electrical trade, the conductor of a 2-wire circuit that is connected to the supply neutral point and earth ground is also referred to as the "neutral". This is formally described in the US and Canadian electrical codes as the "identified" circuit conductor.
TYPES OF EARTHING SYSTEMS International standard IEC 60364 distinguishes three families of earthing arrangements, using the two-letter codes TN, TT, and IT. The first letter indicates the connection between earth and the power-supply equipment (generator or transformer): T : direct connection of a point with earth (French: terre); I : no point is connected with earth (isolation), except perhaps via a high impedance.The second letter indicates the connection between earth and the electrical device being supplied: T : direct connection with earth, independent of any other earth connection in the supply system; N : connection to earth via the supply network.
TN NETWORK
TN-S NETWORK
TN-C NETWORK
TN-C-S NETWORK
TT NETWORK
IT NETWORK
TYPES OF GROUNDING In radio frequency communications In AC power wiring installations Circuit ground versus earth. In lightning protection
In radio frequency communications An electrical connection to earth for as a reference potential for radio frequency antenna signals. High frequency signals can flow to earth through capacitance, capacitance to ground is an important factor in effectiveness of signal grounds. An ideal signal ground maintains zero voltage regardless of how much electrical current flows into ground or out of ground. The resistance at the signal frequency of the electrode-to-earth connection determines its quality, and that quality is improved by increasing the surface area of the electrode in contact with the earth, increasing the depth to which it is driven, using several connected ground rods, increasing the moisture of the soil, improving the conductive mineral content of the soil, and increasing the land area covered by the ground system.
In AC power wiring installations In a mains (AC power) wiring installation, the ground is a wire with an electrical connection to earth, that provides an alternative path to the ground for heavy currents that might otherwise flow through a victim of electric shock. These may be located locally, be far away in the suppliers network or in many cases both. This grounding wire is usually but not always connected to the neutral wire at some point. The ground wire is also usually bonded to pipe work to keep it at the same potential as the electrical ground during a fault. Water supply pipes often used to be used as ground electrodes but this was banned in some countries when plastic pipe such as PVC became popular. This type of ground applies to radio antennas and to lightning protection systems.
Circuit ground versus earth In an electrical circuit operating at signal voltages (usually less than 50 V or so), a common return path that is the zero voltage reference level for the equipment or system. Voltage is a differential quantity, which appears between two points having some electrical potentials. In order to deal only with a voltage (an electrical potential) of a single point, the second point has to be connected to a reference point (ground) having usually zero voltage. This signal ground may or may not actually be connected to a power ground. A system where the system ground is not actually connected to earth is often referred to as a floating ground.
In lightning protection A ground conductor on a lightning protection system is used to dissipate the strike into the earth.
USES A power ground serves to provide a return path for fault currents and therefore allow the fuse or breaker to disconnect the circuit. Filters also connect to the power ground, but this is mainly to stop the power ground carrying noise into the systems which the filters protect, rather than as a direct use of the power ground. In Single Wire Earth Return (SWER) electrical distribution systems, costs are saved by using just a single high voltage conductor for the power grid. This system is mostly used in rural areas where large earth currents will not otherwise cause hazards. Signal grounds serve as return paths for signals and power at low voltages (less than about 50 V) within equipment, and on the signal interconnections between equipment.
GENERAL GROUNDING
GENERATOR EARTHING
VIRTUAL GROUND CONCEPT If two opposite power sources are connected each other by a conductive medium so that their opposite output quantities are superposed (summed), zero or reference level result referred to as virtual ground appears somewhere along the medium. In this "conflict" point, the efforts of the "fighting" sources are "neutralized". The process is associated with continuous energy wasting from both the sources as a result of a continuous energy flow through the medium. Shortly, virtual ground phenomenon is summing of opposite equal quantities associated with continuous energy wasting; virtual ground represents the result of summing two opposite equal quantities.
MULTI POINT GROUND A Multipoint Ground is an alternate type of electrical installation that attempts to solve the Ground Loop and Mains hum problem by creating many alternate paths for electrical energy to find its way back to ground. The distinguishing characteristic of a multipoint ground is the use of many interconnected grounding conductors into a loose grid configuration. There will be many paths between any two points in a multipoint grounding system, rather than the single path found in a star topology ground.
CONCLUSIONGrounding and Earthing systems form the first lineof defense in every type of electrical systems. Thesystem may be a generator/transformer/housinginstallation/generating station/etc. So it is strictlyadvised to know the basic concepts of grounding asfar as electrical engg. is concerned.
EARTHING SYSTEM
EARTHING SYSTEMS
TT SYSTEM
A TT system has a direct connection to the supply source to earth and a direct connection of the installation metalwork to earth. An example is an overhead line supply with earth electrodes, and the mass of earth as a return path as shown below.
Note that only single-phase systems have been shown for simplicity.
TN-S SYSTEM
A TN-S system has the supply source directly connected to earth, the installation metalwork connected to the neutral of the supply source via the lead sheath of the supply cable, and the neutral and protective conductors throughout the whole system performing separate functions.
The resistance around the loop P-B-N-E should be no more than 0.8 ohms.
TN-C-S SYSTEM
A TN-C-S system is as the TN-S but the supply cable sheath is also the neutral, i.e. it forms a combined earth/neutral conductor known as a PEN (protective earthed neutral) conductor.
The installation earth and neutral are separate conductors.
This system is also known as PME (protective multiple earthing).
The resistance around the P-B-N-N loop should be less than 0.35 ohms.
SUMMARY OF EARTHING SYSTEMS
The TT method is used mostly in country areas with overhead transmission lines. In contrast to the TN-S system there is no metallic path from the consumer's terminals back to the sub-station transformer secondary windings. Because the earth path may be of high resistance, a residual current circuit-breaker (R.C.C.B.) is often fitted so that if a fault current flows in the earth path then a trip disconnects the phase supply.
For protection against indirect contact in domestic premises, every socket outlet requires an RCCB with a maximum rated current of 30mA.
The TN-S system of wiring uses the incoming cable sheath as the earth return path and the phase and neutral have separate conductors. The neutral is then connected to earth back at the transformer sub-station.
Remember in TN-S, the T stands for earth (terre), N for neutral and S denotes that the protective (earth) and neutral conductors are separate.
The TN-C-S system has only two conductors in the incoming cable, one phase and the other neutral. The earth is linked to the neutral at the consumer unit. The neutral therefore is really a combined earth/neutral conductor hence the name PME.
In order to avoid the risk of serious electric shock, it is important to provide a path for earth leakage currents to operate the circuit protection, and to endeavour to maintain all metalwork at the same potential. This is achieved by bonding together all metalwork of electrical and non-electrical systems to earth.
The path for leakage currents would then be via the earth itself in TT systems or by a metallic return path in TN-S or TN-C-S systems.
Sunday 18 May 2014
AC GENERATOR ALTERNATOR
AC GENERATOR ALTERNATOR
A.C. generators or alternators (as they are usually called) operate on the same fundamental principles of electromagnetic induction as D.C. generators.
Alternating voltage may be generated by rotating a coil in the magnetic field or by rotating a magnetic field within a stationary coil. The value of the voltage generated depends on-
the number of turns in the coil.
strength of the field.
the speed at which the coil or magnetic field rotates.
A.C. generators or alternators (as they are usually called) operate on the same fundamental principles of electromagnetic induction as D.C. generators.
Alternating voltage may be generated by rotating a coil in the magnetic field or by rotating a magnetic field within a stationary coil. The value of the voltage generated depends on-
the number of turns in the coil.
strength of the field.
the speed at which the coil or magnetic field rotates.
ALL OF DETAILES ACMOTOR
ALL OF DETAILES ACMOTOR
AC motor
From Wikipedia, the free encyclopedia
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An AC motor is an electric motor driven by an alternating current (AC).
It commonly consists of two basic parts, an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field.
There are two main types of AC motors, depending on the type of rotor used. The first type is the induction motor or asynchronous motor; this type relies on a small difference in speed between the rotating magnetic field and the rotor to induce rotor current. The second type is the synchronous motor, which does not rely on induction and as a result can rotate exactly at the supply frequency or a sub-multiple of the supply frequency. The magnetic field on the rotor is either generated by current delivered through slip rings or by a permanent magnet. Other types of motors include eddy current motors, and also AC/DC mechanically commutated machines in which speed is dependent on voltage and winding connection.
Contents [hide]
1 History
2 Induction motor
2.1 Slip
2.2 Polyphase cage rotor
2.3 Polyphase wound rotor
2.4 Two-phase servo motor
2.5 Single-phase induction motor
2.5.1 Shaded-pole motor
2.5.2 Split-phase motor
2.5.2.1 Capacitor start motor
2.5.2.2 Resistance start motor
2.5.2.3 Permanent-split capacitor motor
3 Synchronous motor
3.1 Polyphase synchronous motor
3.2 Single-phase synchronous motor
3.3 Hysteresis synchronous motor
4 Other AC motor types
4.1 Universal motor and series wound motor
4.2 Repulsion motor
4.3 Exterior Rotor
4.4 Sliding rotor motor
4.5 Electronically commutated motor
4.6 Watthour-meter motor
4.7 Slow-speed synchronous timing motor
5 References
6 External links
History[edit]
Drawing from U.S. Patent 381968, illustrating principle of Tesla's alternating current motor.
Alternating current technology was rooted in Michael Faraday’s and Joseph Henry’s 1830-31 discovery that a changing magnetic field can induce an electric current in a circuit. Faraday is usually given credit for this discovery since he published his findings first.[1]
In 1832, French instrument maker Hippolyte Pixii generated a crude form of alternating current when he designed and built the first alternator. It consisted of a revolving horseshoe magnet passing over two wound wire coils.[2]
Because of AC's advantages in long distance high voltage transmission there were many inventors in the United States and Europe during the late 19th century trying to develop workable AC motors.[3] The first person to conceive of a rotating magnetic field was Walter Baily who gave a workable demonstration of his battery-operated polyphase motor aided by a commutator on June 28, 1879 to the Physical Society of London.[4] Nearly identical to Baily’s apparatus, French electrical engineer Marcel Deprez in 1880 published a paper that identified the rotating magnetic field principle and that of a two-phase AC system of currents to produce it.[5] Never practically demonstrated, the design was flawed as one of the two currents was “furnished by the machine itself.”[4] In 1886, English engineer Elihu Thomson built an AC motor by expanding upon the induction-repulsion principle and his wattmeter.[6] In 1887, American inventor Charles Schenk Bradley was the first to patent a two-phase AC power transmission with four wires.
"Commutatorless" alternating current induction motors seem to have been independently invented by Galileo Ferraris and Nikola Tesla. Ferraris demonstrated a working model of his single phase induction motor in 1885 and Tesla built his working two phase induction motor in 1887 and demonstrated it at the American Institute of Electrical Engineers in 1888[7][8][9] (although Tesla claimed that he conceived the rotating magnetic field in 1882).[10] In 1888, Ferraris published his research to the Royal Academy of Sciences in Turin, where he detailed the foundations of motor operation;[11] Tesla, in the same year, was granted a United States patent for his own motor.[12] Working from Ferraris's experiments, Mikhail Dolivo-Dobrovolsky introduced the first three-phase induction motor in 1890, a much more capable design that became the prototype used in Europe and the U.S.[13][14][15] He also invented the first three-phase generator and transformer and combined them into the first complete AC three-phase system in 1891.[16] The three phase motor design was also worked on by the Swiss engineer Charles Eugene Lancelot Brown[13] and other three-phase AC systems were developed by German technician Friedrich August Haselwander and Swedish engineer Jonas Wenström.[17]
Induction motor[edit]
Main article: Induction motor
Slip[edit]
If the rotor of a squirrel cage motor runs at the true synchronous speed, the flux in the rotor at any given place on the rotor would not change, and no current would be created in the squirrel cage. For this reason, ordinary squirrel-cage motors run at some tens of rpm slower than synchronous speed. Because the rotating field (or equivalent pulsating field) effectively rotates faster than the rotor, it could be said to slip past the surface of the rotor. The difference between synchronous speed and actual speed is called slip, and loading the motor increases the amount of slip as the motor slows down slightly. Even with no load, internal mechanical losses prevent the slip from being zero.
The speed of the AC motor is determined primarily by the frequency of the AC supply and the number of poles in the stator winding, according to the relation:
where
Ns = Synchronous speed, in revolutions per minute
F = AC power frequency
p = Number of poles per phase winding
Actual RPM for an induction motor will be less than this calculated synchronous speed by an amount known as slip, that increases with the torque produced. With no load, the speed will be very close to synchronous. When loaded, standard motors have between 2-3% slip, special motors may have up to 7% slip, and a class of motors known as torque motors are rated to operate at 100% slip (0 RPM/full stall).
The slip of the AC motor is calculated by:
where
Nr = Rotational speed, in revolutions per minute.
S = Normalised Slip, 0 to 1.
As an example, a typical four-pole motor running on 60 Hz might have a nameplate rating of 1725 RPM at full load, while its calculated speed is 1800 RPM.
The speed in this type of motor has traditionally been altered by having additional sets of coils or poles in the motor that can be switched on and off to change the speed of magnetic field rotation. However, developments in power electronics mean that the frequency of the power supply can also now be varied to provide a smoother control of the motor speed.
This kind of rotor is the basic hardware for induction regulators, which is an exception of the use of rotating magnetic field as pure electrical (not electromechanical) application.
Polyphase cage rotor[edit]
Most common AC motors use the squirrel cage rotor, which will be found in virtually all domestic and light industrial alternating current motors. The squirrel cage refers to the rotating exercise cage for pet animals. The motor takes its name from the shape of its rotor "windings"- a ring at either end of the rotor, with bars connecting the rings running the length of the rotor. It is typically cast aluminum or copper poured between the iron laminates of the rotor, and usually only the end rings will be visible. The vast majority of the rotor currents will flow through the bars rather than the higher-resistance and usually varnished laminates. Very low voltages at very high currents are typical in the bars and end rings; high efficiency motors will often use cast copper to reduce the resistance in the rotor.
In operation, the squirrel cage motor may be viewed as a transformer with a rotating secondary. When the rotor is not rotating in sync with the magnetic field, large rotor currents are induced; the large rotor currents magnetize the rotor and interact with the stator's magnetic fields to bring the rotor almost into synchronization with the stator's field. An unloaded squirrel cage motor at rated no-load speed will consume electrical power only to maintain rotor speed against friction and resistance losses. As the mechanical load increases, so will the electrical load - the electrical load is inherently related to the mechanical load. This is similar to a transformer, where the primary's electrical load is related to the secondary's electrical load.
This is why a squirrel cage blower motor may cause household lights to dim upon starting, but does not dim the lights on startup when its fan belt (and therefore mechanical load) is removed. Furthermore, a stalled squirrel cage motor (overloaded or with a jammed shaft) will consume current limited only by circuit resistance as it attempts to start. Unless something else limits the current (or cuts it off completely) overheating and destruction of the winding insulation is the likely outcome.
Virtually every washing machine, dishwasher, standalone fan, record player, etc. uses some variant of a squirrel cage motor.[citation needed]
Polyphase wound rotor[edit]
An alternate design, called the wound rotor, is used when variable speed is required. In this case, the rotor has the same number of poles as the stator and the windings are made of wire, connected to slip rings on the shaft. Carbon brushes connect the slip rings to an external controller such as a variable resistor that allows changing the motor's slip rate. In certain high-power variable speed wound-rotor drives, the slip-frequency energy is captured, rectified and returned to the power supply through an inverter. With bidirectionally controlled power, the wound-rotor becomes an active participant in the energy conversion process with the wound-rotor doubly fed configuration showing twice the power density.
Compared to squirrel cage rotors and without considering brushless wound-rotor doubly fed technology, wound rotor motors are expensive and require maintenance of the slip rings and brushes, but they were the standard form for variable speed control before the advent of compact power electronic devices. Transistorized inverters with variable-frequency drive can now be used for speed control, and wound rotor motors are becoming less common.
Several methods of starting a polyphase motor are used. Where the large inrush current and high starting torque can be permitted, the motor can be started across the line, by applying full line voltage to the terminals (direct-on-line, DOL). Where it is necessary to limit the starting inrush current (where the motor is large compared with the short-circuit capacity of the supply), reduced voltage starting using either series inductors, an autotransformer, thyristors, or other devices are used. A technique sometimes used is (star-delta, YΔ) starting, where the motor coils are initially connected in star for acceleration of the load, then switched to delta when the load is up to speed. This technique is more common in Europe than in North America. Transistorized drives can directly vary the applied voltage as required by the starting characteristics of the motor and load.
This type of motor is becoming more common in traction applications such as locomotives, where it is known as the asynchronous traction motor.
Two-phase servo motor[edit]
A typical two-phase AC servo-motor has a squirrel cage rotor and a field consisting of two windings:
a constant-voltage (AC) main winding.
a control-voltage (AC) winding in quadrature (i.e., 90 degrees phase shifted) with the main winding so as to produce a rotating magnetic field. Reversing phase makes the motor reverse.
An AC servo amplifier, a linear power amplifier, feeds the control winding. The electrical resistance of the rotor is made high intentionally so that the speed/torque curve is fairly linear. Two-phase servo motors are inherently high-speed, low-torque devices, heavily geared down to drive the load.
Single-phase induction motor[edit]
Three-phase motors produce a rotating magnetic field. However, when only single-phase power is available, the rotating magnetic field must be produced using other means. Several methods are commonly used:
Shaded-pole motor[edit]
A common single-phase motor is the shaded-pole motor and is used in devices requiring low starting torque, such as electric fans or the drain pump of washing machines and dishwashers or in other small household appliances. In this motor, small single-turn copper "shading coils" create the moving magnetic field. Part of each pole is encircled by a copper coil or strap; the induced current in the strap opposes the change of flux through the coil. This causes a time lag in the flux passing through the shading coil, so that the maximum field intensity moves across the pole face on each cycle. This produces a low level rotating magnetic field which is large enough to turn both the rotor and its attached load. As the rotor picks up speed the torque builds up to its full level as the principal magnetic field is rotating relative to the rotating rotor.
A reversible shaded-pole motor was made by Barber-Colman several decades ago. It had a single field coil, and two principal poles, each split halfway to create two pairs of poles. Each of these four "half-poles" carried a coil, and the coils of diagonally opposite half-poles were connected to a pair of terminals. One terminal of each pair was common, so only three terminals were needed in all.
The motor would not start with the terminals open; connecting the common to one other made the motor run one way, and connecting common to the other made it run the other way. These motors were used in industrial and scientific devices.
An unusual, adjustable-speed, low-torque shaded-pole motor could be found in traffic-light and advertising-lighting controllers. The pole faces were parallel and relatively close to each other, with the disc centred between them, something like the disc in a watthour meter. Each pole face was split, and had a shading coil on one part; the shading coils were on the parts that faced each other. Both shading coils were probably closer to the main coil; they could have both been farther away, without affecting the operating principle, just the direction of rotation.
Applying AC to the coil created a field that progressed in the gap between the poles. The plane of the stator core was approximately tangential to an imaginary circle on the disc, so the travelling magnetic field dragged the disc and made it rotate.
The stator was mounted on a pivot so it could be positioned for the desired speed and then clamped in position. Keeping in mind that the effective speed of the travelling magnetic field in the gap was constant, placing the poles nearer to the centre of the disc made it run relatively faster, and toward the edge, slower.
It is possible that these motors are still in use in some older installations.
Split-phase motor[edit]
Another common single-phase AC motor is the split-phase induction motor,[18] commonly used in major appliances such as air conditioners and clothes dryers. Compared to the shaded pole motor, these motors can generally provide much greater starting torque.
A split-phase motor has a startup winding separate from the main winding. When the motor is starting, the startup winding is connected to the power source via a centrifugal switch which is closed at low speed. In non-reversible models, the starting winding is wound with fewer turns of smaller wire than the main winding, so it has a lower inductance (L) and higher resistance (R). In reversible motors, the start and run windings are exactly identical. The L/R ratio creates a small phase shift, not more than about 30 degrees, between the flux due to the main winding and the flux of the starting winding. The starting direction of rotation is determined by the order of the connections of the startup winding relative to the running winding.
The phase of the magnetic field in this startup winding is shifted from the phase of the supply power, which creates a moving magnetic field to start the motor. Once the motor reaches near design operating speed, the centrifugal switch opens, disconnecting the startup winding from the power source. The motor then operates solely on the main winding. The purpose of disconnecting the startup winding is to eliminate the energy loss due to its added resistance.
Capacitor start motor[edit]
Schematic of a capacitor start motor.
A capacitor start motor is a split-phase induction motor with a starting capacitor inserted in series with the startup winding, creating an LC circuit which produces a greater phase shift (and so, a much greater starting torque) than both split-phase and shaded pole motors. The capacitor naturally adds expense to such motors.
Resistance start motor[edit]
A resistance start motor is a split-phase induction motor with a starter inserted in series with the startup winding, creating reactance. This added starter provides assistance in the starting and initial direction of rotation.
Permanent-split capacitor motor[edit]
Another variation is the permanent-split capacitor (PSC) motor (also known as a capacitor start and run motor).[19] This motor operates similarly to the capacitor-start motor described above, but there is no centrifugal starting switch,[19] and what correspond to the "start" windings (second windings) are permanently connected to the power source (through a run capacitor), along with the run windings.[19] PSC motors are frequently used in air handlers, blowers, and fans (including ceiling fans) and other cases where variable speeds are desired.
A capacitor that ranges from 1 to 100 microfarads is connected in series with the start (auxiliary) winding and remains in the circuit during the entire run cycle.[19] The start and run windings are identical in a reversible motor,[19] and reverse motion can be achieved by reversing the wiring of the 2 windings,[19] causing the other winding to be connected through the capacitor, and therefore act as the "start" winding. Non-reversible motors have smaller, thinner start windings, similar to non-reversible split phase motors. By changing taps on the running winding but keeping the load constant, the motor can be made to run at different speeds.
Three-phase motors can be converted to PSC motors by making common two windings and connecting the third via a capacitor to act as a start winding. However, the power rating needs to be at least 50% larger than for a comparable single-phase motor due to an unused winding.[20]
Synchronous motor[edit]
Main article: Synchronous motor
Three-phase system with rotating magnetic fields.
Polyphase synchronous motor[edit]
If connections to the rotor coils of a three-phase motor are taken out on slip-rings and fed a separate field current to create a continuous magnetic field (or if the rotor consists of a permanent magnet), the result is called a synchronous motor because the rotor will rotate synchronously with the rotating magnetic field produced by the polyphase electrical supply.
The synchronous motor can also be used as an alternator.
Nowadays, synchronous motors are frequently driven by transistorized variable-frequency drives. This greatly eases the problem of starting the massive rotor of a large synchronous motor. They may also be started as induction motors using a squirrel-cage winding that shares the common rotor: once the motor reaches synchronous speed, no current is induced in the squirrel-cage winding so it has little effect on the synchronous operation of the motor, aside from stabilizing the motor speed on load changes.
Synchronous motors are occasionally used as traction motors; the TGV may be the best-known example of such use.
One use for this type of motor is its use in a power factor correction scheme. They are referred to as synchronous condensers. This exploits a feature of the machine where it consumes power at a leading power factor when its rotor is over excited. It thus appears to the supply to be a capacitor, and could thus be used to correct the lagging power factor that is usually presented to the electric supply by inductive loads. The excitation is adjusted until a near unity power factor is obtained (often automatically). Machines used for this purpose are easily identified as they have no shaft extensions. Synchronous motors are valued in any case because their power factor is much better than that of induction motors, making them preferred for very high power applications.
Some of the largest AC motors are pumped-storage hydroelectricity generators that are operated as synchronous motors to pump water to a reservoir at a higher elevation for later use to generate electricity using the same machinery. Six 500-megawatt generators are installed in the Bath County Pumped Storage Station in Virginia, USA. When pumping, each unit can produce 642,800 horsepower (479.3 megawatts).[21].
Single-phase synchronous motor[edit]
Small single-phase AC motors can also be designed with magnetized rotors (or several variations on that idea; see "Hysteresis synchronous motors" below).
If a conventional squirrel-cage rotor has flats ground on it to create salient poles and increase reluctance, it will start conventionally, but will run synchronously, although it can provide only a modest torque at synchronous speed. This is known as a reluctance motor.
Because inertia makes it difficult to instantly accelerate the rotor from stopped to synchronous speed, these motors normally require some sort of special feature to get started. Some include a squirrel-cage structure to bring the rotor close to synchronous speed. Various other designs use a small induction motor (which may share the same field coils and rotor as the synchronous motor) or a very light rotor with a one-way mechanism (to ensure that the rotor starts in the "forward" direction). In the latter instance, applying AC power creates chaotic (or seemingly chaotic) jumping movement back and forth; such a motor will always start, but lacking the anti-reversal mechanism, the direction it runs is unpredictable. The Hammond organ tone generator used a non-self-starting synchronous motor (until comparatively recently), and had an auxiliary conventional shaded-pole starting motor. A spring-loaded auxiliary manual starting switch connected power to this second motor for a few seconds.
Hysteresis synchronous motor[edit]
These motors are relatively costly, and are used where exact speed (assuming an exact-frequency AC source) as well as rotation with a very small amount of fast variations in speed (called 'flutter" in audio recordings) is essential. Applications included tape recorder capstan drives (the motor shaft could be the capstan), and, before the advent of crystal control, motion picture cameras and recorders. Their distinguishing feature is their rotor, which is a smooth cylinder of a magnetic alloy that stays magnetized, but can be demagnetized fairly easily as well as re-magnetized with poles in a new location. Hysteresis refers to how the magnetic flux in the metal lags behind the external magnetizing force; for instance, to demagnetize such a material, one could apply a magnetizing field of opposite polarity to that which originally magnetized the material. These motors have a stator like those of capacitor-run squirrel-cage induction motors. On startup, when slip decreases sufficiently, the rotor becomes magnetized by the stator's field, and the poles stay in place. The motor then runs at synchronous speed as if the rotor were a permanent magnet. When stopped and restarted, the poles are likely to form at different locations. For a given design, torque at synchronous speed is only relatively modest, and the motor can run at below synchronous speed. In simple words, it is lagging magnetic field behind magnetic flux.
Other AC motor types[edit]
Universal motor and series wound motor[edit]
Main article: Universal motor
A universal motor is a design that can operate on either AC or DC power. In universal motors the stator and rotor of a brushed DC motor are both wound and supplied from an external source, with the torque being a function of the rotor current times the stator current so reversing the current in both rotor and stator does not reverse the rotation. Universal motors can run on AC as well as DC provided the frequency is not so high that the inductive reactance of the stator winding and/or eddy current losses become problems. Nearly all universal motors are series-wound because their stators have relatively few turns, minimizing inductance. Universal motors are compact, have high starting torque and can be varied in speed over a wide range with relatively simple controls such as rheostats and PWM choppers. Compared with induction motors, universal motors do have some drawbacks inherent to their brushes and commutators: relatively high levels of electrical and acoustic noise, low reliability and more frequent required maintenance.
Universal motors are widely used in small home appliances and hand power tools. Until the 1970s they dominated electric traction (electric, including diesel-electric railway and road vehicles); many traction power networks still use special low frequencies such as 16.7 and 25 Hz to overcome the aforementioned problems with losses and reactance. Still widely used, universal traction motors have been increasingly displaced by polyphase AC induction and permanent magnet motors with variable-frequency drives made possible by modern power semiconductor devices.
Repulsion motor[edit]
Main article: Repulsion motor
Repulsion motors are wound-rotor single-phase AC motors that are a type of induction motor. In a repulsion motor, the armature brushes are shorted together rather than connected in series with the field, as is done with universal motors. By transformer action, the stator induces currents in the rotor, which create torque by repulsion instead of attraction as in other motors. Several types of repulsion motors have been manufactured, but the repulsion-start induction-run (RS-IR) motor has been used most frequently. The RS-IR motor has a centrifugal switch that shorts all segments of the commutator so that the motor operates as an induction motor once it is close to full speed. Some of these motors also lift the brushes out of contact with source voltage regulation. Few repulsion motors of any type are sold as of 2005.
Exterior Rotor[edit]
Where speed stability is important, some AC motors (such as some Papst motors) have the stator on the inside and the rotor on the outside to optimize inertia and cooling.
Sliding rotor motor[edit]
AC Motor with sliding rotors
A conical rotor brake motor incorporates the brake as an integral part of the conical sliding rotor. When the motor is at rest, a spring acts on the sliding rotor and forces the brake ring against the brake cap in the motor, holding the rotor stationary. When the motor is energized, its magnetic field generates both an axial and a radial component. The axial component overcomes the spring force, releasing the brake; while the radial component causes the rotor to turn. There is no additional brake control required.
The high starting torque and low inertia of the conical rotor brake motor has proven to be ideal for the demands of high cycle dynamic drives in applications since the motor was invented, designed and introduced over 50 years ago. This type of motor configuration was first introduced in the USA in 1963.
Single-speed or two speed motors are designed for coupling to gear motor system gearboxes. Conical rotor brake motors are also used to power micro speed drives.
Motors of this type can also be found on overhead cranes and hoists. The micro speed unit combines two motors and an intermediate gear reducer. These are used for applications where extreme mechanical positioning accuracy and high cycling capability are needed. The micro speed unit combines a “main” conical rotor brake motor for rapid speed and a “micro” conical rotor brake motor for slow or positioning speed. The intermediate gearbox allows a range of ratios, and motors of different speeds can be combined to produce high ratios between high and low speed.
Electronically commutated motor[edit]
Main article: Brushless DC electric motor
Electronically commutated (EC) motors are electric motors powered by direct-current (DC) electricity and having electronic commutation systems, rather than mechanical commutators and brushes. The current-to-torque and frequency-to-speed relationships of BLDC motors are linear. While the motor coils are powered by DC, power may be rectified from AC within the casing.
Watthour-meter motor[edit]
These are two-phase induction motors with permanent magnets to retard the rotor so its speed is accurately proportional to the power passing through the meter. The rotor is an aluminium-alloy disc, and currents induced into it react with the field from the stator.
A split-phase watthour meter has a stator with three coils facing the disc. The magnetic circuit is completed by a C-shaped core of permeable iron. The "voltage" coil above the disc is in parallel with the supply; its many turns have a high inductance/resistance ratio (Q) so its current and magnetic field are the time integral of the applied voltage, lagging it by 90 degrees. This magnetic field passes down perpendicularly through the disc, inducing circular eddy currents in the plane of the disc centered on the field. These induced currents are proportional to the time derivative of the magnetic field, leading it by 90 degrees. This puts the eddy currents in phase with the voltage applied to the voltage coil, just as the current induced in the secondary of a transformer with a resistive load is in phase with the voltage applied to its primary.
The eddy currents pass directly above the pole pieces of two "current" coils under the disc, each wound with a few turns of heavy-gauge wire whose inductive reactance is small compared to the load impedance. These coils connect the supply to the load, producing a magnetic field in phase with the load current. This field passes from the pole of one current coil up perpendicularly through the disc and back down through the disc to the pole of the other current coil, with a completed magnetic circuit back to the first current coil. As these fields cross the disc, they pass through the eddy currents induced in it by the voltage coil producing a Lorentz force on the disc mutually perpendicular to both. Assuming power is flowing to the load, the flux from the left current coil crosses the disc upwards where the eddy current flows radially toward the center of the disc producing (by the right hand rule) a torque driving the front of the disc to the right. Similarly, the flux crosses down through the disc to the right current coil where the eddy current flows radially away from the disc center, again producing a torque driving the front of the disc to the right. When the AC polarity reverses, the eddy currents in the disc and the direction of the magnetic flux from the current coils both change, leaving the direction of the torque unchanged.
The torque is thus proportional to the instantaneous line voltage times the instantaneous load current, automatically correcting for power factor. The disc is braked by a permanent magnet so that speed is proportional to torque and the disc mechanically integrates real power. The mechanical dial on the meter reads disc rotations and the total net energy delivered to the load. (If the load supplies power to the grid, the disc rotates backwards unless prevented by a ratchet, thus making net metering possible.)
In a split-phase watthour meter the voltage coil is connected between the two "hot" (line) terminals (240V in North America) and two separate current coils are connected between the corresponding line and load terminals. No connection to the system neutral is needed to correctly handle combined line-to-neutral and line-to-line loads. Line-to-line loads draw the same current through both current coils and spin the meter twice as fast as a line-to-neutral load drawing the same current through only a single current coil, correctly registering the power drawn by the line-to-line load as twice that of the line-to-neutral load.
Other variations of the same design are used for polyphase (e.g., 3-phase) power.
Slow-speed synchronous timing motor[edit]
Representative are low-torque synchronous motors with a multi-pole hollow cylindrical magnet (internal poles) surrounding the stator structure. An aluminum cup supports the magnet. The stator has one coil, coaxial with the shaft. At each end of the coil are a pair of circular plates with rectangular teeth on their edges, formed so they are parallel with the shaft. They are the stator poles. One of the pair of discs distributes the coil's flux directly, while the other receives flux that has passed through a common shading coil. The poles are rather narrow, and between the poles leading from one end of the coil are an identical set leading from the other end. In all, this creates a repeating sequence of four poles, unshaded alternating with shaded, that creates a circumferential traveling field to which the rotor's magnetic poles rapidly synchronize. Some stepping motors have a similar structure.
References
AC motor
From Wikipedia, the free encyclopedia
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An AC motor is an electric motor driven by an alternating current (AC).
It commonly consists of two basic parts, an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field.
There are two main types of AC motors, depending on the type of rotor used. The first type is the induction motor or asynchronous motor; this type relies on a small difference in speed between the rotating magnetic field and the rotor to induce rotor current. The second type is the synchronous motor, which does not rely on induction and as a result can rotate exactly at the supply frequency or a sub-multiple of the supply frequency. The magnetic field on the rotor is either generated by current delivered through slip rings or by a permanent magnet. Other types of motors include eddy current motors, and also AC/DC mechanically commutated machines in which speed is dependent on voltage and winding connection.
Contents [hide]
1 History
2 Induction motor
2.1 Slip
2.2 Polyphase cage rotor
2.3 Polyphase wound rotor
2.4 Two-phase servo motor
2.5 Single-phase induction motor
2.5.1 Shaded-pole motor
2.5.2 Split-phase motor
2.5.2.1 Capacitor start motor
2.5.2.2 Resistance start motor
2.5.2.3 Permanent-split capacitor motor
3 Synchronous motor
3.1 Polyphase synchronous motor
3.2 Single-phase synchronous motor
3.3 Hysteresis synchronous motor
4 Other AC motor types
4.1 Universal motor and series wound motor
4.2 Repulsion motor
4.3 Exterior Rotor
4.4 Sliding rotor motor
4.5 Electronically commutated motor
4.6 Watthour-meter motor
4.7 Slow-speed synchronous timing motor
5 References
6 External links
History[edit]
Drawing from U.S. Patent 381968, illustrating principle of Tesla's alternating current motor.
Alternating current technology was rooted in Michael Faraday’s and Joseph Henry’s 1830-31 discovery that a changing magnetic field can induce an electric current in a circuit. Faraday is usually given credit for this discovery since he published his findings first.[1]
In 1832, French instrument maker Hippolyte Pixii generated a crude form of alternating current when he designed and built the first alternator. It consisted of a revolving horseshoe magnet passing over two wound wire coils.[2]
Because of AC's advantages in long distance high voltage transmission there were many inventors in the United States and Europe during the late 19th century trying to develop workable AC motors.[3] The first person to conceive of a rotating magnetic field was Walter Baily who gave a workable demonstration of his battery-operated polyphase motor aided by a commutator on June 28, 1879 to the Physical Society of London.[4] Nearly identical to Baily’s apparatus, French electrical engineer Marcel Deprez in 1880 published a paper that identified the rotating magnetic field principle and that of a two-phase AC system of currents to produce it.[5] Never practically demonstrated, the design was flawed as one of the two currents was “furnished by the machine itself.”[4] In 1886, English engineer Elihu Thomson built an AC motor by expanding upon the induction-repulsion principle and his wattmeter.[6] In 1887, American inventor Charles Schenk Bradley was the first to patent a two-phase AC power transmission with four wires.
"Commutatorless" alternating current induction motors seem to have been independently invented by Galileo Ferraris and Nikola Tesla. Ferraris demonstrated a working model of his single phase induction motor in 1885 and Tesla built his working two phase induction motor in 1887 and demonstrated it at the American Institute of Electrical Engineers in 1888[7][8][9] (although Tesla claimed that he conceived the rotating magnetic field in 1882).[10] In 1888, Ferraris published his research to the Royal Academy of Sciences in Turin, where he detailed the foundations of motor operation;[11] Tesla, in the same year, was granted a United States patent for his own motor.[12] Working from Ferraris's experiments, Mikhail Dolivo-Dobrovolsky introduced the first three-phase induction motor in 1890, a much more capable design that became the prototype used in Europe and the U.S.[13][14][15] He also invented the first three-phase generator and transformer and combined them into the first complete AC three-phase system in 1891.[16] The three phase motor design was also worked on by the Swiss engineer Charles Eugene Lancelot Brown[13] and other three-phase AC systems were developed by German technician Friedrich August Haselwander and Swedish engineer Jonas Wenström.[17]
Induction motor[edit]
Main article: Induction motor
Slip[edit]
If the rotor of a squirrel cage motor runs at the true synchronous speed, the flux in the rotor at any given place on the rotor would not change, and no current would be created in the squirrel cage. For this reason, ordinary squirrel-cage motors run at some tens of rpm slower than synchronous speed. Because the rotating field (or equivalent pulsating field) effectively rotates faster than the rotor, it could be said to slip past the surface of the rotor. The difference between synchronous speed and actual speed is called slip, and loading the motor increases the amount of slip as the motor slows down slightly. Even with no load, internal mechanical losses prevent the slip from being zero.
The speed of the AC motor is determined primarily by the frequency of the AC supply and the number of poles in the stator winding, according to the relation:
where
Ns = Synchronous speed, in revolutions per minute
F = AC power frequency
p = Number of poles per phase winding
Actual RPM for an induction motor will be less than this calculated synchronous speed by an amount known as slip, that increases with the torque produced. With no load, the speed will be very close to synchronous. When loaded, standard motors have between 2-3% slip, special motors may have up to 7% slip, and a class of motors known as torque motors are rated to operate at 100% slip (0 RPM/full stall).
The slip of the AC motor is calculated by:
where
Nr = Rotational speed, in revolutions per minute.
S = Normalised Slip, 0 to 1.
As an example, a typical four-pole motor running on 60 Hz might have a nameplate rating of 1725 RPM at full load, while its calculated speed is 1800 RPM.
The speed in this type of motor has traditionally been altered by having additional sets of coils or poles in the motor that can be switched on and off to change the speed of magnetic field rotation. However, developments in power electronics mean that the frequency of the power supply can also now be varied to provide a smoother control of the motor speed.
This kind of rotor is the basic hardware for induction regulators, which is an exception of the use of rotating magnetic field as pure electrical (not electromechanical) application.
Polyphase cage rotor[edit]
Most common AC motors use the squirrel cage rotor, which will be found in virtually all domestic and light industrial alternating current motors. The squirrel cage refers to the rotating exercise cage for pet animals. The motor takes its name from the shape of its rotor "windings"- a ring at either end of the rotor, with bars connecting the rings running the length of the rotor. It is typically cast aluminum or copper poured between the iron laminates of the rotor, and usually only the end rings will be visible. The vast majority of the rotor currents will flow through the bars rather than the higher-resistance and usually varnished laminates. Very low voltages at very high currents are typical in the bars and end rings; high efficiency motors will often use cast copper to reduce the resistance in the rotor.
In operation, the squirrel cage motor may be viewed as a transformer with a rotating secondary. When the rotor is not rotating in sync with the magnetic field, large rotor currents are induced; the large rotor currents magnetize the rotor and interact with the stator's magnetic fields to bring the rotor almost into synchronization with the stator's field. An unloaded squirrel cage motor at rated no-load speed will consume electrical power only to maintain rotor speed against friction and resistance losses. As the mechanical load increases, so will the electrical load - the electrical load is inherently related to the mechanical load. This is similar to a transformer, where the primary's electrical load is related to the secondary's electrical load.
This is why a squirrel cage blower motor may cause household lights to dim upon starting, but does not dim the lights on startup when its fan belt (and therefore mechanical load) is removed. Furthermore, a stalled squirrel cage motor (overloaded or with a jammed shaft) will consume current limited only by circuit resistance as it attempts to start. Unless something else limits the current (or cuts it off completely) overheating and destruction of the winding insulation is the likely outcome.
Virtually every washing machine, dishwasher, standalone fan, record player, etc. uses some variant of a squirrel cage motor.[citation needed]
Polyphase wound rotor[edit]
An alternate design, called the wound rotor, is used when variable speed is required. In this case, the rotor has the same number of poles as the stator and the windings are made of wire, connected to slip rings on the shaft. Carbon brushes connect the slip rings to an external controller such as a variable resistor that allows changing the motor's slip rate. In certain high-power variable speed wound-rotor drives, the slip-frequency energy is captured, rectified and returned to the power supply through an inverter. With bidirectionally controlled power, the wound-rotor becomes an active participant in the energy conversion process with the wound-rotor doubly fed configuration showing twice the power density.
Compared to squirrel cage rotors and without considering brushless wound-rotor doubly fed technology, wound rotor motors are expensive and require maintenance of the slip rings and brushes, but they were the standard form for variable speed control before the advent of compact power electronic devices. Transistorized inverters with variable-frequency drive can now be used for speed control, and wound rotor motors are becoming less common.
Several methods of starting a polyphase motor are used. Where the large inrush current and high starting torque can be permitted, the motor can be started across the line, by applying full line voltage to the terminals (direct-on-line, DOL). Where it is necessary to limit the starting inrush current (where the motor is large compared with the short-circuit capacity of the supply), reduced voltage starting using either series inductors, an autotransformer, thyristors, or other devices are used. A technique sometimes used is (star-delta, YΔ) starting, where the motor coils are initially connected in star for acceleration of the load, then switched to delta when the load is up to speed. This technique is more common in Europe than in North America. Transistorized drives can directly vary the applied voltage as required by the starting characteristics of the motor and load.
This type of motor is becoming more common in traction applications such as locomotives, where it is known as the asynchronous traction motor.
Two-phase servo motor[edit]
A typical two-phase AC servo-motor has a squirrel cage rotor and a field consisting of two windings:
a constant-voltage (AC) main winding.
a control-voltage (AC) winding in quadrature (i.e., 90 degrees phase shifted) with the main winding so as to produce a rotating magnetic field. Reversing phase makes the motor reverse.
An AC servo amplifier, a linear power amplifier, feeds the control winding. The electrical resistance of the rotor is made high intentionally so that the speed/torque curve is fairly linear. Two-phase servo motors are inherently high-speed, low-torque devices, heavily geared down to drive the load.
Single-phase induction motor[edit]
Three-phase motors produce a rotating magnetic field. However, when only single-phase power is available, the rotating magnetic field must be produced using other means. Several methods are commonly used:
Shaded-pole motor[edit]
A common single-phase motor is the shaded-pole motor and is used in devices requiring low starting torque, such as electric fans or the drain pump of washing machines and dishwashers or in other small household appliances. In this motor, small single-turn copper "shading coils" create the moving magnetic field. Part of each pole is encircled by a copper coil or strap; the induced current in the strap opposes the change of flux through the coil. This causes a time lag in the flux passing through the shading coil, so that the maximum field intensity moves across the pole face on each cycle. This produces a low level rotating magnetic field which is large enough to turn both the rotor and its attached load. As the rotor picks up speed the torque builds up to its full level as the principal magnetic field is rotating relative to the rotating rotor.
A reversible shaded-pole motor was made by Barber-Colman several decades ago. It had a single field coil, and two principal poles, each split halfway to create two pairs of poles. Each of these four "half-poles" carried a coil, and the coils of diagonally opposite half-poles were connected to a pair of terminals. One terminal of each pair was common, so only three terminals were needed in all.
The motor would not start with the terminals open; connecting the common to one other made the motor run one way, and connecting common to the other made it run the other way. These motors were used in industrial and scientific devices.
An unusual, adjustable-speed, low-torque shaded-pole motor could be found in traffic-light and advertising-lighting controllers. The pole faces were parallel and relatively close to each other, with the disc centred between them, something like the disc in a watthour meter. Each pole face was split, and had a shading coil on one part; the shading coils were on the parts that faced each other. Both shading coils were probably closer to the main coil; they could have both been farther away, without affecting the operating principle, just the direction of rotation.
Applying AC to the coil created a field that progressed in the gap between the poles. The plane of the stator core was approximately tangential to an imaginary circle on the disc, so the travelling magnetic field dragged the disc and made it rotate.
The stator was mounted on a pivot so it could be positioned for the desired speed and then clamped in position. Keeping in mind that the effective speed of the travelling magnetic field in the gap was constant, placing the poles nearer to the centre of the disc made it run relatively faster, and toward the edge, slower.
It is possible that these motors are still in use in some older installations.
Split-phase motor[edit]
Another common single-phase AC motor is the split-phase induction motor,[18] commonly used in major appliances such as air conditioners and clothes dryers. Compared to the shaded pole motor, these motors can generally provide much greater starting torque.
A split-phase motor has a startup winding separate from the main winding. When the motor is starting, the startup winding is connected to the power source via a centrifugal switch which is closed at low speed. In non-reversible models, the starting winding is wound with fewer turns of smaller wire than the main winding, so it has a lower inductance (L) and higher resistance (R). In reversible motors, the start and run windings are exactly identical. The L/R ratio creates a small phase shift, not more than about 30 degrees, between the flux due to the main winding and the flux of the starting winding. The starting direction of rotation is determined by the order of the connections of the startup winding relative to the running winding.
The phase of the magnetic field in this startup winding is shifted from the phase of the supply power, which creates a moving magnetic field to start the motor. Once the motor reaches near design operating speed, the centrifugal switch opens, disconnecting the startup winding from the power source. The motor then operates solely on the main winding. The purpose of disconnecting the startup winding is to eliminate the energy loss due to its added resistance.
Capacitor start motor[edit]
Schematic of a capacitor start motor.
A capacitor start motor is a split-phase induction motor with a starting capacitor inserted in series with the startup winding, creating an LC circuit which produces a greater phase shift (and so, a much greater starting torque) than both split-phase and shaded pole motors. The capacitor naturally adds expense to such motors.
Resistance start motor[edit]
A resistance start motor is a split-phase induction motor with a starter inserted in series with the startup winding, creating reactance. This added starter provides assistance in the starting and initial direction of rotation.
Permanent-split capacitor motor[edit]
Another variation is the permanent-split capacitor (PSC) motor (also known as a capacitor start and run motor).[19] This motor operates similarly to the capacitor-start motor described above, but there is no centrifugal starting switch,[19] and what correspond to the "start" windings (second windings) are permanently connected to the power source (through a run capacitor), along with the run windings.[19] PSC motors are frequently used in air handlers, blowers, and fans (including ceiling fans) and other cases where variable speeds are desired.
A capacitor that ranges from 1 to 100 microfarads is connected in series with the start (auxiliary) winding and remains in the circuit during the entire run cycle.[19] The start and run windings are identical in a reversible motor,[19] and reverse motion can be achieved by reversing the wiring of the 2 windings,[19] causing the other winding to be connected through the capacitor, and therefore act as the "start" winding. Non-reversible motors have smaller, thinner start windings, similar to non-reversible split phase motors. By changing taps on the running winding but keeping the load constant, the motor can be made to run at different speeds.
Three-phase motors can be converted to PSC motors by making common two windings and connecting the third via a capacitor to act as a start winding. However, the power rating needs to be at least 50% larger than for a comparable single-phase motor due to an unused winding.[20]
Synchronous motor[edit]
Main article: Synchronous motor
Three-phase system with rotating magnetic fields.
Polyphase synchronous motor[edit]
If connections to the rotor coils of a three-phase motor are taken out on slip-rings and fed a separate field current to create a continuous magnetic field (or if the rotor consists of a permanent magnet), the result is called a synchronous motor because the rotor will rotate synchronously with the rotating magnetic field produced by the polyphase electrical supply.
The synchronous motor can also be used as an alternator.
Nowadays, synchronous motors are frequently driven by transistorized variable-frequency drives. This greatly eases the problem of starting the massive rotor of a large synchronous motor. They may also be started as induction motors using a squirrel-cage winding that shares the common rotor: once the motor reaches synchronous speed, no current is induced in the squirrel-cage winding so it has little effect on the synchronous operation of the motor, aside from stabilizing the motor speed on load changes.
Synchronous motors are occasionally used as traction motors; the TGV may be the best-known example of such use.
One use for this type of motor is its use in a power factor correction scheme. They are referred to as synchronous condensers. This exploits a feature of the machine where it consumes power at a leading power factor when its rotor is over excited. It thus appears to the supply to be a capacitor, and could thus be used to correct the lagging power factor that is usually presented to the electric supply by inductive loads. The excitation is adjusted until a near unity power factor is obtained (often automatically). Machines used for this purpose are easily identified as they have no shaft extensions. Synchronous motors are valued in any case because their power factor is much better than that of induction motors, making them preferred for very high power applications.
Some of the largest AC motors are pumped-storage hydroelectricity generators that are operated as synchronous motors to pump water to a reservoir at a higher elevation for later use to generate electricity using the same machinery. Six 500-megawatt generators are installed in the Bath County Pumped Storage Station in Virginia, USA. When pumping, each unit can produce 642,800 horsepower (479.3 megawatts).[21].
Single-phase synchronous motor[edit]
Small single-phase AC motors can also be designed with magnetized rotors (or several variations on that idea; see "Hysteresis synchronous motors" below).
If a conventional squirrel-cage rotor has flats ground on it to create salient poles and increase reluctance, it will start conventionally, but will run synchronously, although it can provide only a modest torque at synchronous speed. This is known as a reluctance motor.
Because inertia makes it difficult to instantly accelerate the rotor from stopped to synchronous speed, these motors normally require some sort of special feature to get started. Some include a squirrel-cage structure to bring the rotor close to synchronous speed. Various other designs use a small induction motor (which may share the same field coils and rotor as the synchronous motor) or a very light rotor with a one-way mechanism (to ensure that the rotor starts in the "forward" direction). In the latter instance, applying AC power creates chaotic (or seemingly chaotic) jumping movement back and forth; such a motor will always start, but lacking the anti-reversal mechanism, the direction it runs is unpredictable. The Hammond organ tone generator used a non-self-starting synchronous motor (until comparatively recently), and had an auxiliary conventional shaded-pole starting motor. A spring-loaded auxiliary manual starting switch connected power to this second motor for a few seconds.
Hysteresis synchronous motor[edit]
These motors are relatively costly, and are used where exact speed (assuming an exact-frequency AC source) as well as rotation with a very small amount of fast variations in speed (called 'flutter" in audio recordings) is essential. Applications included tape recorder capstan drives (the motor shaft could be the capstan), and, before the advent of crystal control, motion picture cameras and recorders. Their distinguishing feature is their rotor, which is a smooth cylinder of a magnetic alloy that stays magnetized, but can be demagnetized fairly easily as well as re-magnetized with poles in a new location. Hysteresis refers to how the magnetic flux in the metal lags behind the external magnetizing force; for instance, to demagnetize such a material, one could apply a magnetizing field of opposite polarity to that which originally magnetized the material. These motors have a stator like those of capacitor-run squirrel-cage induction motors. On startup, when slip decreases sufficiently, the rotor becomes magnetized by the stator's field, and the poles stay in place. The motor then runs at synchronous speed as if the rotor were a permanent magnet. When stopped and restarted, the poles are likely to form at different locations. For a given design, torque at synchronous speed is only relatively modest, and the motor can run at below synchronous speed. In simple words, it is lagging magnetic field behind magnetic flux.
Other AC motor types[edit]
Universal motor and series wound motor[edit]
Main article: Universal motor
A universal motor is a design that can operate on either AC or DC power. In universal motors the stator and rotor of a brushed DC motor are both wound and supplied from an external source, with the torque being a function of the rotor current times the stator current so reversing the current in both rotor and stator does not reverse the rotation. Universal motors can run on AC as well as DC provided the frequency is not so high that the inductive reactance of the stator winding and/or eddy current losses become problems. Nearly all universal motors are series-wound because their stators have relatively few turns, minimizing inductance. Universal motors are compact, have high starting torque and can be varied in speed over a wide range with relatively simple controls such as rheostats and PWM choppers. Compared with induction motors, universal motors do have some drawbacks inherent to their brushes and commutators: relatively high levels of electrical and acoustic noise, low reliability and more frequent required maintenance.
Universal motors are widely used in small home appliances and hand power tools. Until the 1970s they dominated electric traction (electric, including diesel-electric railway and road vehicles); many traction power networks still use special low frequencies such as 16.7 and 25 Hz to overcome the aforementioned problems with losses and reactance. Still widely used, universal traction motors have been increasingly displaced by polyphase AC induction and permanent magnet motors with variable-frequency drives made possible by modern power semiconductor devices.
Repulsion motor[edit]
Main article: Repulsion motor
Repulsion motors are wound-rotor single-phase AC motors that are a type of induction motor. In a repulsion motor, the armature brushes are shorted together rather than connected in series with the field, as is done with universal motors. By transformer action, the stator induces currents in the rotor, which create torque by repulsion instead of attraction as in other motors. Several types of repulsion motors have been manufactured, but the repulsion-start induction-run (RS-IR) motor has been used most frequently. The RS-IR motor has a centrifugal switch that shorts all segments of the commutator so that the motor operates as an induction motor once it is close to full speed. Some of these motors also lift the brushes out of contact with source voltage regulation. Few repulsion motors of any type are sold as of 2005.
Exterior Rotor[edit]
Where speed stability is important, some AC motors (such as some Papst motors) have the stator on the inside and the rotor on the outside to optimize inertia and cooling.
Sliding rotor motor[edit]
AC Motor with sliding rotors
A conical rotor brake motor incorporates the brake as an integral part of the conical sliding rotor. When the motor is at rest, a spring acts on the sliding rotor and forces the brake ring against the brake cap in the motor, holding the rotor stationary. When the motor is energized, its magnetic field generates both an axial and a radial component. The axial component overcomes the spring force, releasing the brake; while the radial component causes the rotor to turn. There is no additional brake control required.
The high starting torque and low inertia of the conical rotor brake motor has proven to be ideal for the demands of high cycle dynamic drives in applications since the motor was invented, designed and introduced over 50 years ago. This type of motor configuration was first introduced in the USA in 1963.
Single-speed or two speed motors are designed for coupling to gear motor system gearboxes. Conical rotor brake motors are also used to power micro speed drives.
Motors of this type can also be found on overhead cranes and hoists. The micro speed unit combines two motors and an intermediate gear reducer. These are used for applications where extreme mechanical positioning accuracy and high cycling capability are needed. The micro speed unit combines a “main” conical rotor brake motor for rapid speed and a “micro” conical rotor brake motor for slow or positioning speed. The intermediate gearbox allows a range of ratios, and motors of different speeds can be combined to produce high ratios between high and low speed.
Electronically commutated motor[edit]
Main article: Brushless DC electric motor
Electronically commutated (EC) motors are electric motors powered by direct-current (DC) electricity and having electronic commutation systems, rather than mechanical commutators and brushes. The current-to-torque and frequency-to-speed relationships of BLDC motors are linear. While the motor coils are powered by DC, power may be rectified from AC within the casing.
Watthour-meter motor[edit]
These are two-phase induction motors with permanent magnets to retard the rotor so its speed is accurately proportional to the power passing through the meter. The rotor is an aluminium-alloy disc, and currents induced into it react with the field from the stator.
A split-phase watthour meter has a stator with three coils facing the disc. The magnetic circuit is completed by a C-shaped core of permeable iron. The "voltage" coil above the disc is in parallel with the supply; its many turns have a high inductance/resistance ratio (Q) so its current and magnetic field are the time integral of the applied voltage, lagging it by 90 degrees. This magnetic field passes down perpendicularly through the disc, inducing circular eddy currents in the plane of the disc centered on the field. These induced currents are proportional to the time derivative of the magnetic field, leading it by 90 degrees. This puts the eddy currents in phase with the voltage applied to the voltage coil, just as the current induced in the secondary of a transformer with a resistive load is in phase with the voltage applied to its primary.
The eddy currents pass directly above the pole pieces of two "current" coils under the disc, each wound with a few turns of heavy-gauge wire whose inductive reactance is small compared to the load impedance. These coils connect the supply to the load, producing a magnetic field in phase with the load current. This field passes from the pole of one current coil up perpendicularly through the disc and back down through the disc to the pole of the other current coil, with a completed magnetic circuit back to the first current coil. As these fields cross the disc, they pass through the eddy currents induced in it by the voltage coil producing a Lorentz force on the disc mutually perpendicular to both. Assuming power is flowing to the load, the flux from the left current coil crosses the disc upwards where the eddy current flows radially toward the center of the disc producing (by the right hand rule) a torque driving the front of the disc to the right. Similarly, the flux crosses down through the disc to the right current coil where the eddy current flows radially away from the disc center, again producing a torque driving the front of the disc to the right. When the AC polarity reverses, the eddy currents in the disc and the direction of the magnetic flux from the current coils both change, leaving the direction of the torque unchanged.
The torque is thus proportional to the instantaneous line voltage times the instantaneous load current, automatically correcting for power factor. The disc is braked by a permanent magnet so that speed is proportional to torque and the disc mechanically integrates real power. The mechanical dial on the meter reads disc rotations and the total net energy delivered to the load. (If the load supplies power to the grid, the disc rotates backwards unless prevented by a ratchet, thus making net metering possible.)
In a split-phase watthour meter the voltage coil is connected between the two "hot" (line) terminals (240V in North America) and two separate current coils are connected between the corresponding line and load terminals. No connection to the system neutral is needed to correctly handle combined line-to-neutral and line-to-line loads. Line-to-line loads draw the same current through both current coils and spin the meter twice as fast as a line-to-neutral load drawing the same current through only a single current coil, correctly registering the power drawn by the line-to-line load as twice that of the line-to-neutral load.
Other variations of the same design are used for polyphase (e.g., 3-phase) power.
Slow-speed synchronous timing motor[edit]
Representative are low-torque synchronous motors with a multi-pole hollow cylindrical magnet (internal poles) surrounding the stator structure. An aluminum cup supports the magnet. The stator has one coil, coaxial with the shaft. At each end of the coil are a pair of circular plates with rectangular teeth on their edges, formed so they are parallel with the shaft. They are the stator poles. One of the pair of discs distributes the coil's flux directly, while the other receives flux that has passed through a common shading coil. The poles are rather narrow, and between the poles leading from one end of the coil are an identical set leading from the other end. In all, this creates a repeating sequence of four poles, unshaded alternating with shaded, that creates a circumferential traveling field to which the rotor's magnetic poles rapidly synchronize. Some stepping motors have a similar structure.
References
A
SLIP
If the rotor of a squirrel cage motor runs at the true synchronous speed, the flux in the rotor at any given place on the rotor would nonge, and no current would be created in the squirrel cage. For this reason, ordinary squirrel-cage motors run at some tens of rpm slower than synchronous speed. Because the rotating field (or equivalent pulsating field) effectively rotates faster than the rotor, it could be said to slip past the surface of the rotor. The difference between synchronous speed and actual speed is called slip, and loading the motor increases the amount of slip as the motor slows down slightly. Even with no load, internal mechanical losses prevent the slip from being zero.
The speed of the AC motor is determined primarily by the frequency of the AC supply and the number of poles in the stator winding, according to the relation:
where
Ns = Synchronous speed, in revolutions per minute
F = AC power frequency
p = Number of poles per phase winding
Actual RPM for an induction motor will be less than this calculated synchronous speed by an amount known as slip, that increases with the torque produced. With no load, the speed will be very close to synchronous. When loaded, standard motors have between 2-3% slip, special motors may have up to 7% slip, and a class of motors known as torque motors are rated to operate at 100% slip (0 RPM/full stall).
The slip of the AC motor is calculated by:
where
Nr = Rotational speed, in revolutions per minute.
S = Normalised Slip, 0 to 1.
As an example, a typical four-pole motor running on 60 Hz might have a nameplate rating of 1725 RPM at full load, while its calculated speed is 1800 RPM.
The speed in this type of motor has traditionally been altered by having additional sets of coils or poles in the motor that can be switched on and off to change the speed of magnetic field rotation. However, developments in power electronics mean that the frequency of the power supply can also now be varied to provide a smoother control of the motor speed.
This kind of rotor is the basic hardware for induction regulators, which is an exception of the use of rotating magnetic field as pure electrical (not electromechanical) application.
If the rotor of a squirrel cage motor runs at the true synchronous speed, the flux in the rotor at any given place on the rotor would nonge, and no current would be created in the squirrel cage. For this reason, ordinary squirrel-cage motors run at some tens of rpm slower than synchronous speed. Because the rotating field (or equivalent pulsating field) effectively rotates faster than the rotor, it could be said to slip past the surface of the rotor. The difference between synchronous speed and actual speed is called slip, and loading the motor increases the amount of slip as the motor slows down slightly. Even with no load, internal mechanical losses prevent the slip from being zero.
The speed of the AC motor is determined primarily by the frequency of the AC supply and the number of poles in the stator winding, according to the relation:
where
Ns = Synchronous speed, in revolutions per minute
F = AC power frequency
p = Number of poles per phase winding
Actual RPM for an induction motor will be less than this calculated synchronous speed by an amount known as slip, that increases with the torque produced. With no load, the speed will be very close to synchronous. When loaded, standard motors have between 2-3% slip, special motors may have up to 7% slip, and a class of motors known as torque motors are rated to operate at 100% slip (0 RPM/full stall).
The slip of the AC motor is calculated by:
where
Nr = Rotational speed, in revolutions per minute.
S = Normalised Slip, 0 to 1.
As an example, a typical four-pole motor running on 60 Hz might have a nameplate rating of 1725 RPM at full load, while its calculated speed is 1800 RPM.
The speed in this type of motor has traditionally been altered by having additional sets of coils or poles in the motor that can be switched on and off to change the speed of magnetic field rotation. However, developments in power electronics mean that the frequency of the power supply can also now be varied to provide a smoother control of the motor speed.
This kind of rotor is the basic hardware for induction regulators, which is an exception of the use of rotating magnetic field as pure electrical (not electromechanical) application.
AC MOTOR
AC MOTOR
An AC motor is an electric motor driven by an alternating current (AC).
It commonly consists of two basic parts, an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field.
There are two main types of AC motors, depending on the type of rotor used. The first type is the induction motor or asynchronous motor; this type relies on a small difference in speed between the rotating magnetic field and the rotor to induce rotor current. The second type is the synchronous motor, which does not rely on induction and as a result can rotate exactly at the supply frequency or a sub-multiple of the supply frequency. The magnetic field on the rotor is either generated by current delivered through slip rings or by a permanent magnet. Other types of motors include eddy current motors, and also AC/DC mechanically commutated machines in which speed is dependent on voltage and winding connection.
An AC motor is an electric motor driven by an alternating current (AC).
It commonly consists of two basic parts, an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft that is given a torque by the rotating field.
There are two main types of AC motors, depending on the type of rotor used. The first type is the induction motor or asynchronous motor; this type relies on a small difference in speed between the rotating magnetic field and the rotor to induce rotor current. The second type is the synchronous motor, which does not rely on induction and as a result can rotate exactly at the supply frequency or a sub-multiple of the supply frequency. The magnetic field on the rotor is either generated by current delivered through slip rings or by a permanent magnet. Other types of motors include eddy current motors, and also AC/DC mechanically commutated machines in which speed is dependent on voltage and winding connection.
TYPES AND METHODS OF SPEED CONTROL OF DC MOTOR
TYPES AND METHODS OF SPEED CONTROL OF DC MOTOR
Armature Control of DC Series Motor
Speed adjustment of dc series motor by armature control may be done by any one of the methods that follow,
1. Armature resistance control method: This is the most common method employed. Here the controlling resistance is connected directly in series with the supply to the motor as shown in the fig.
diagram
The power loss in the control resistance of dc series motor can be neglected because this control method is utilized for a large portion of time for reducing the speed under light load condition. This method of speed control is most economical for constant torque. This method of speed control is employed for dc series motor driving cranes, hoists, trains etc.
2. Shunted armature control: The combination of a rheostat shunting the armature and a rheostat in series with the armature is involved in this method of speed control. The voltage applied to the armature is varies by varying series rheostat R 1. The exciting current can be varied by varying the armature shunting resistance R2. This method of speed control is not economical due to considerable power losses in speed controlling resistances. Here speed control is obtained over wide range but below normal speed.
Diagram :
3. Armature terminal voltage control: The speed control of dc series motor can be accomplished by supplying the power to the motor from a separate variable voltage supply. This method involves high cost so it rarely used.
Field Control of DC Series Motor
The speed of dc motor can be controlled by this method by any one of the following ways –
1. Field diverter method: This method uses a diverter. Here the field flux can be reduced by shunting a portion of motor current around the series field. Lesser the diverter resistance less is the field current, less flux therefore more speed. This method gives speed above normal and the method is used in electric drives in which speed should rise sharply as soon as load is decreased.diagram
2. Tapped Field control: This is another method of increasing the speed by reducing the flux and it is done by lowering number of turns of field winding through which current flows. In this method a number of tapping from field winding are brought outside . This method is employed in electric traction.
Diagram
Speed Control of DC Shunt Motor
Speed of dc shunt motor is controlled by the factors stated below
Field Control of DC Shunt Motor
By this method speed control is obtained by any one of the following means –
1. Field rheostat control of DC Shunt Motor: In this method , speed variation is accomplished by means of a variable resistance inserted in series with the shunt field . An increase in controlling resistances reduces the field current with a reduction in flux and an increase in speed. This method of speed control is independent of load on the motor. Power wasted in controlling resistance is very less as field current is a small value. This method of speed control is also used in DC compound motor.
Limitations of this method of speed control:
A. Creeping speeds cannot be obtained.
B. Top speeds only obtained at reduced torque
C. The speed is maximum at minimum value of flux, which is governed by the demagnetizing effect of armature reaction on the field.
2. Field voltage control: This method requires a variable voltage supply for the field circuit which is separated from the main power supply to which the armature is connected. Such a variable supply can be obtained by an electronic rectifier.
Armature Control of DC Shunt Motor
Speed control by this method involves two ways . These are :
1. Armature resistance control : In this method armature circuit is provided with a variable resistance. Field is directly connected across the supply so flux is not changed due to variation of series resistance. This is applied for dc shunt motor. This method is used in printing press, cranes, hoists where speeds lower than rated is used for a short period only.
2. Armature voltage control: This method of speed control needs a variable source of voltage separated from the source supplying the field current. This method avoids disadvantages of poor speed regulation and low efficiency of armature-resistance control methods. The basic adjustable armature voltage control method of speed d control is accomplished by means of an adjustable voltage generator is called Ward Leonard system. This method involves using a motor –generator (M-G) set. This method is best suited for steel rolling mills, paper machines, elevators, mine hoists, etc.
Advantages of this method –
A. Very fine speed control over whole range in both directions
B. Uniform acceleration is obtained
C. Good speed regulation
Disadvantages –
A. Costly arrangement is needed , floor space required is more
B. Low efficiency at light loads
Armature Control of DC Series Motor
Speed adjustment of dc series motor by armature control may be done by any one of the methods that follow,
1. Armature resistance control method: This is the most common method employed. Here the controlling resistance is connected directly in series with the supply to the motor as shown in the fig.
diagram
The power loss in the control resistance of dc series motor can be neglected because this control method is utilized for a large portion of time for reducing the speed under light load condition. This method of speed control is most economical for constant torque. This method of speed control is employed for dc series motor driving cranes, hoists, trains etc.
2. Shunted armature control: The combination of a rheostat shunting the armature and a rheostat in series with the armature is involved in this method of speed control. The voltage applied to the armature is varies by varying series rheostat R 1. The exciting current can be varied by varying the armature shunting resistance R2. This method of speed control is not economical due to considerable power losses in speed controlling resistances. Here speed control is obtained over wide range but below normal speed.
Diagram :
3. Armature terminal voltage control: The speed control of dc series motor can be accomplished by supplying the power to the motor from a separate variable voltage supply. This method involves high cost so it rarely used.
Field Control of DC Series Motor
The speed of dc motor can be controlled by this method by any one of the following ways –
1. Field diverter method: This method uses a diverter. Here the field flux can be reduced by shunting a portion of motor current around the series field. Lesser the diverter resistance less is the field current, less flux therefore more speed. This method gives speed above normal and the method is used in electric drives in which speed should rise sharply as soon as load is decreased.diagram
2. Tapped Field control: This is another method of increasing the speed by reducing the flux and it is done by lowering number of turns of field winding through which current flows. In this method a number of tapping from field winding are brought outside . This method is employed in electric traction.
Diagram
Speed Control of DC Shunt Motor
Speed of dc shunt motor is controlled by the factors stated below
Field Control of DC Shunt Motor
By this method speed control is obtained by any one of the following means –
1. Field rheostat control of DC Shunt Motor: In this method , speed variation is accomplished by means of a variable resistance inserted in series with the shunt field . An increase in controlling resistances reduces the field current with a reduction in flux and an increase in speed. This method of speed control is independent of load on the motor. Power wasted in controlling resistance is very less as field current is a small value. This method of speed control is also used in DC compound motor.
Limitations of this method of speed control:
A. Creeping speeds cannot be obtained.
B. Top speeds only obtained at reduced torque
C. The speed is maximum at minimum value of flux, which is governed by the demagnetizing effect of armature reaction on the field.
2. Field voltage control: This method requires a variable voltage supply for the field circuit which is separated from the main power supply to which the armature is connected. Such a variable supply can be obtained by an electronic rectifier.
Armature Control of DC Shunt Motor
Speed control by this method involves two ways . These are :
1. Armature resistance control : In this method armature circuit is provided with a variable resistance. Field is directly connected across the supply so flux is not changed due to variation of series resistance. This is applied for dc shunt motor. This method is used in printing press, cranes, hoists where speeds lower than rated is used for a short period only.
2. Armature voltage control: This method of speed control needs a variable source of voltage separated from the source supplying the field current. This method avoids disadvantages of poor speed regulation and low efficiency of armature-resistance control methods. The basic adjustable armature voltage control method of speed d control is accomplished by means of an adjustable voltage generator is called Ward Leonard system. This method involves using a motor –generator (M-G) set. This method is best suited for steel rolling mills, paper machines, elevators, mine hoists, etc.
Advantages of this method –
A. Very fine speed control over whole range in both directions
B. Uniform acceleration is obtained
C. Good speed regulation
Disadvantages –
A. Costly arrangement is needed , floor space required is more
B. Low efficiency at light loads
Speed Control of DC Motor
Speed Control of DC Motor
Speed control means intentional change of the drive speed to a value required for performing the specific work process. Speed control is a different concept from speed regulation where there is natural change in speed due change in load on the shaft. Speed control is either done manually by the operator or by means of some automatic control device.
One of the important features of dc motor is that its speed can be controlled with relative ease. We know that the expression of speed control dc motor is given as,
Therefore speed (N ) of 3 types of dc motor – SERIES, SHUNT AND COMPOUND can be controlled by changing the quantities on RHS of the expression. So speed can be varied by changing
(i) terminal voltage of the armature V ,
(ii) external resistance in armature circuit R and
(iii) flux per pole φ .
The first two cases involve change that affects armature circuit and the third one involves change in magnetic field. Therefore speed control of dc motor is classified as
1) armature control methods and
2) field control methods
.
Speed control means intentional change of the drive speed to a value required for performing the specific work process. Speed control is a different concept from speed regulation where there is natural change in speed due change in load on the shaft. Speed control is either done manually by the operator or by means of some automatic control device.
One of the important features of dc motor is that its speed can be controlled with relative ease. We know that the expression of speed control dc motor is given as,
Therefore speed (N ) of 3 types of dc motor – SERIES, SHUNT AND COMPOUND can be controlled by changing the quantities on RHS of the expression. So speed can be varied by changing
(i) terminal voltage of the armature V ,
(ii) external resistance in armature circuit R and
(iii) flux per pole φ .
The first two cases involve change that affects armature circuit and the third one involves change in magnetic field. Therefore speed control of dc motor is classified as
1) armature control methods and
2) field control methods
.
Construction of DC Motor
A DC motor like we all know is a device that deals in the conversion of electrical energy to mechanical energy and this is essentially brought about by two major parts required for the construction of dc motor, namely.
1) Stator – The static part that houses the field windings and receives the supply and,
2) Rotor – The rotating part that brings about the mechanical rotations.
Other than that there are several subsidiary parts namely the
3) Yoke of dc motor.
4) Poles of dc motor.
5) Field winding of dc motor.
6) Armature winding of dc motor.
7) Commutator of dc motor.
8) Brushes of dc motor.
All these parts put together configures the total construction of a dc motor.
Now let’s do a detailed discussion about all the essential parts of dc motor.
Essential Parts of DC Machine
Yoke of DC Motor
The magnetic frame or the yoke of dc motor made up of cast iron or steel and forms an integral part of the stator or the static part of the motor. Its main function is to form a protective covering over the inner sophisticated parts of the motor and provide support to the armature. It also supports the field system by housing the magnetic poles and field winding of the dc motor.
Poles of DC Motor
The magnetic poles of DC motor are structures fitted onto the inner wall of the yoke with screws. The construction of magnetic poles basically comprises of two parts namely, the pole core and the pole shoe stacked together under hydraulic pressure and then attached to the yoke. These two structures are assigned for different purposes, the pole core is of small cross sectional area and its function is to just hold the pole shoe over the yoke, whereas the pole shoe having a relatively larger cross-sectional area spreads the flux produced over the air gap between the stator and rotor to reduce the loss due to reluctance. The pole shoe also carries slots for the field windings that produce the field flux.
Field Winding of DC Motor
The field winding of dc motor are made with field coils (copper wire) wound over the slots of the pole shoes in such a manner that when field current flows through it, then adjacent poles have opposite polarity are produced. The field winding basically form an electromagnet, that produces field flux within which the rotor armature of the dc motor rotates, and results in the effective flux cutting.
Armature Winding of DC Motor
The armature winding of dc motor is attached to the rotor, or the rotating part of the machine, and as a result is subjected to altering magnetic field in the path of its rotation which directly results in magnetic losses. For this reason the rotor is made of armature core, that’s made with several low-hysteresis silicon steel lamination, to reduce the magnetic losses like hysteresis and eddy current loss respectively. These laminated steel sheets are stacked together to form the cylindrical structure of the armature core.
The armature core are provided with slots made of the same material as the core to which the armature winding made with several turns of copper wire distributed uniformly over the entire periphery of the core. The slot openings a shut with fibrous wedges to prevent the conductor from plying out due to the high centrifugal force produced during the rotation of the armature, in presence of supply current and field.
The construction of armature winding of dc motor can be of two types:-
Lap Winding
In this case the number of parallel paths between conductors A is equal to the number of poles P.
i.e A = P
>
***An easy way of remembering it is by remembering the word LAP-----→ L A=P
Wave Winding
Here in this case, the number of parallel paths between conductors A is always equal to 2 irrespective of the number of poles. Hence the machine designs are made accordingly.
Commutator of DC Motor
The commutator of dc motor is a cylindrical structure made up of copper segments stacked together, but insulated from each other by mica. Its main function as far as the dc motor is concerned is to commute or relay the supply current from the mains to the armature winding housed over a rotating structure through the brushes of dc motor.
Brushes of DC Motor
The brushes of dc motor are made with carbon or graphite structures, making sliding contact over the rotating commutator. The brushes are used to relay the electric current from external circuit to the rotating commutator form where it flows into the armature winding. So, the commutator and brush unit of the dc motor is concerned with transmitting the power from the static electrical circuit to the mechanically rotating region or the rotor
A DC motor like we all know is a device that deals in the conversion of electrical energy to mechanical energy and this is essentially brought about by two major parts required for the construction of dc motor, namely.
1) Stator – The static part that houses the field windings and receives the supply and,
2) Rotor – The rotating part that brings about the mechanical rotations.
Other than that there are several subsidiary parts namely the
3) Yoke of dc motor.
4) Poles of dc motor.
5) Field winding of dc motor.
6) Armature winding of dc motor.
7) Commutator of dc motor.
8) Brushes of dc motor.
All these parts put together configures the total construction of a dc motor.
Now let’s do a detailed discussion about all the essential parts of dc motor.
Essential Parts of DC Machine
Yoke of DC Motor
The magnetic frame or the yoke of dc motor made up of cast iron or steel and forms an integral part of the stator or the static part of the motor. Its main function is to form a protective covering over the inner sophisticated parts of the motor and provide support to the armature. It also supports the field system by housing the magnetic poles and field winding of the dc motor.
Poles of DC Motor
The magnetic poles of DC motor are structures fitted onto the inner wall of the yoke with screws. The construction of magnetic poles basically comprises of two parts namely, the pole core and the pole shoe stacked together under hydraulic pressure and then attached to the yoke. These two structures are assigned for different purposes, the pole core is of small cross sectional area and its function is to just hold the pole shoe over the yoke, whereas the pole shoe having a relatively larger cross-sectional area spreads the flux produced over the air gap between the stator and rotor to reduce the loss due to reluctance. The pole shoe also carries slots for the field windings that produce the field flux.
Field Winding of DC Motor
The field winding of dc motor are made with field coils (copper wire) wound over the slots of the pole shoes in such a manner that when field current flows through it, then adjacent poles have opposite polarity are produced. The field winding basically form an electromagnet, that produces field flux within which the rotor armature of the dc motor rotates, and results in the effective flux cutting.
Armature Winding of DC Motor
The armature winding of dc motor is attached to the rotor, or the rotating part of the machine, and as a result is subjected to altering magnetic field in the path of its rotation which directly results in magnetic losses. For this reason the rotor is made of armature core, that’s made with several low-hysteresis silicon steel lamination, to reduce the magnetic losses like hysteresis and eddy current loss respectively. These laminated steel sheets are stacked together to form the cylindrical structure of the armature core.
The armature core are provided with slots made of the same material as the core to which the armature winding made with several turns of copper wire distributed uniformly over the entire periphery of the core. The slot openings a shut with fibrous wedges to prevent the conductor from plying out due to the high centrifugal force produced during the rotation of the armature, in presence of supply current and field.
The construction of armature winding of dc motor can be of two types:-
Lap Winding
In this case the number of parallel paths between conductors A is equal to the number of poles P.
i.e A = P
>
***An easy way of remembering it is by remembering the word LAP-----→ L A=P
Wave Winding
Here in this case, the number of parallel paths between conductors A is always equal to 2 irrespective of the number of poles. Hence the machine designs are made accordingly.
Commutator of DC Motor
The commutator of dc motor is a cylindrical structure made up of copper segments stacked together, but insulated from each other by mica. Its main function as far as the dc motor is concerned is to commute or relay the supply current from the mains to the armature winding housed over a rotating structure through the brushes of dc motor.
Brushes of DC Motor
The brushes of dc motor are made with carbon or graphite structures, making sliding contact over the rotating commutator. The brushes are used to relay the electric current from external circuit to the rotating commutator form where it flows into the armature winding. So, the commutator and brush unit of the dc motor is concerned with transmitting the power from the static electrical circuit to the mechanically rotating region or the rotor
The working principle behind any DC motor is the attraction and repulsion of magnets. The simplest motors use electromagnets on a shaft, with permanent magnets in the case of the motor that attract and repel the electromagnets. The reason for using electromagnets is so that it is possible to flip their magnetic field (their north and south poles).
So the electromagnet is attracted to one of the permanent magnets. As soon as it reaches the permanent magnet, it’s north and south poles flip so that it is repelled from that magnet and attracted to the other permanent magnet. This video shows you the parts and how they fit together:
So the electromagnet is attracted to one of the permanent magnets. As soon as it reaches the permanent magnet, it’s north and south poles flip so that it is repelled from that magnet and attracted to the other permanent magnet. This video shows you the parts and how they fit together:
Detailed Description of a DC Motor
Detailed Description of a DC Motor
To understand the DC motor in details lets consider the diagram below,
The direct current motor is represented by the circle in the center, on which is mounted the brushes, where we connect the external terminals, from where supply voltage is given. On the mechanical terminal we have a shaft coming out of the Motor, and connected to the armature, and the armature-shaft is coupled to the mechanical load. On the supply terminals we represent the armature resistance Ra in series. Now, let the input voltage E, is applied across the brushes. Electric current which flows through the rotor armature via brushes, in presence of the magnetic field, produces a torque Tg . Due to this torque Tg the dc motor armature rotates. As the armature conductors are carrying currents and the armature rotates inside the stator magnetic field, it also produces an emf Eb in the manner very similar to that of a generator. The generated Emf Eb is directed opposite to the supplied voltage and is known as the back Emf, as it counters the forward voltage.
The back emf like in case of a generator is represented by
Where, P = no of poles
φ = flux per pole
Z= No. of conductors
A = No. of parallel paths
and N is the speed of the DC Motor.
So from the above equation we can see Eb is proportional to speed ‘N’. That is whenever a direct current motor rotates, it results in the generation of back Emf. Now lets represent the rotor speed by ω in rad/sec. So Eb is proportional to ω.
So when the speed of the motor is reduced by the application of load, Eb decreases. Thus the voltage difference between supply voltage and back emf increases that means E − Eb increases. Due to this increased voltage difference, armature current will increase and therefore torque and hence speed increases. Thus a DC Motor is capable of maintaining the same speed under variable load.
Now armature current Ia is represented by
Now at starting,speed ω = 0 so at starting Eb = 0.
Now since the armature winding electrical resistance Ra is small, this motor has a very high starting current in the absence of back Emf. As a result we need to use a starter for starting a DC Motor.
Now as the motor continues to rotate, the back Emf starts being generated and gradually the current decreases as the motor picks up speed.
To understand the DC motor in details lets consider the diagram below,
The direct current motor is represented by the circle in the center, on which is mounted the brushes, where we connect the external terminals, from where supply voltage is given. On the mechanical terminal we have a shaft coming out of the Motor, and connected to the armature, and the armature-shaft is coupled to the mechanical load. On the supply terminals we represent the armature resistance Ra in series. Now, let the input voltage E, is applied across the brushes. Electric current which flows through the rotor armature via brushes, in presence of the magnetic field, produces a torque Tg . Due to this torque Tg the dc motor armature rotates. As the armature conductors are carrying currents and the armature rotates inside the stator magnetic field, it also produces an emf Eb in the manner very similar to that of a generator. The generated Emf Eb is directed opposite to the supplied voltage and is known as the back Emf, as it counters the forward voltage.
The back emf like in case of a generator is represented by
Where, P = no of poles
φ = flux per pole
Z= No. of conductors
A = No. of parallel paths
and N is the speed of the DC Motor.
So from the above equation we can see Eb is proportional to speed ‘N’. That is whenever a direct current motor rotates, it results in the generation of back Emf. Now lets represent the rotor speed by ω in rad/sec. So Eb is proportional to ω.
So when the speed of the motor is reduced by the application of load, Eb decreases. Thus the voltage difference between supply voltage and back emf increases that means E − Eb increases. Due to this increased voltage difference, armature current will increase and therefore torque and hence speed increases. Thus a DC Motor is capable of maintaining the same speed under variable load.
Now armature current Ia is represented by
Now at starting,speed ω = 0 so at starting Eb = 0.
Now since the armature winding electrical resistance Ra is small, this motor has a very high starting current in the absence of back Emf. As a result we need to use a starter for starting a DC Motor.
Now as the motor continues to rotate, the back Emf starts being generated and gradually the current decreases as the motor picks up speed.
principle of DC MOTOR
principle of DC MOTOR
Principle of DC Moto
This DC or direct current motor works on the principal, when a current carrying conductor is placed in a magnetic field, it experiences a torque and has a tendency to move. This is known as motoring action. If the direction of electric current in the wire is reversed, the direction of rotation also reverses. When magnetic field and electric field interact they produce a mechanical force, and based on that the working principle of dc motor established. The direction of rotation of a this motor is given by Fleming’s left hand rule, which states that if the index finger, middle finger and thumb of your left hand are extended mutually perpendicular to each other and if the index finger represents the direction of magnetic field, middle finger indicates the direction of electric current, then the thumb represents the direction in which force is experienced by the shaft of the dc motor.
Structurally and construction wise a direct current motor is exactly similar to a DC generator, but electrically it is just the opposite. Here we unlike a generator we supply electrical energy to the input port and derive mechanical energy from the output port. We can represent it by the block diagram shown below.
Here in a DC motor, the supply voltage E and electric current I is given to the electrical port or the input port and we derive the mechanical output i.e. torque T and speed ω from the mechanical port or output port.
Principle of DC Moto
This DC or direct current motor works on the principal, when a current carrying conductor is placed in a magnetic field, it experiences a torque and has a tendency to move. This is known as motoring action. If the direction of electric current in the wire is reversed, the direction of rotation also reverses. When magnetic field and electric field interact they produce a mechanical force, and based on that the working principle of dc motor established. The direction of rotation of a this motor is given by Fleming’s left hand rule, which states that if the index finger, middle finger and thumb of your left hand are extended mutually perpendicular to each other and if the index finger represents the direction of magnetic field, middle finger indicates the direction of electric current, then the thumb represents the direction in which force is experienced by the shaft of the dc motor.
Structurally and construction wise a direct current motor is exactly similar to a DC generator, but electrically it is just the opposite. Here we unlike a generator we supply electrical energy to the input port and derive mechanical energy from the output port. We can represent it by the block diagram shown below.
Here in a DC motor, the supply voltage E and electric current I is given to the electrical port or the input port and we derive the mechanical output i.e. torque T and speed ω from the mechanical port or output port.
dc motor
What is DC Motor ?
Electrical motors are everywhere around us. Almost all the electro-mechanical movements we see around us are caused either by an A.C. or a DC motor. Here we will be exploring this kind of motors. This is a device that converts DC electrical energy to a mechanical en
Electrical motors are everywhere around us. Almost all the electro-mechanical movements we see around us are caused either by an A.C. or a DC motor. Here we will be exploring this kind of motors. This is a device that converts DC electrical energy to a mechanical en
Thursday 15 May 2014
squirrelcage induction motor,
1. Remove the blower motor assembly by disconnecting its wiring harness and unbolting it, using a ratchet and socket. The location of the blower motor varies among Read More »
A: Lab-3: Squirrel-Cage Induction Motor Xm Xl R R Xl s - Courses
courses.ece.ubc.ca/365/Labs/Lab3_Manual.pdf
Lab-3: Squirrel-Cage Induction Motor ... industrial ¼ HP Squirrel-Cage Induction .... 4: Wiring diagram for taking the phase voltage and current measurements. Read More »
Popular Q&A
Q: How to Remove a Squirrel Cage From a Furnace Motor Shaft.
A: 1. Turn off the power to the furnace at the circuit breaker. 2. Open the front access panel to the furnace by releasing the catches and pulling the cover off. 3. Loosen the screws to the control panel in front of the squirrel cage, if there is one, Read More »
Source: http://www.ehow.com/how_7811521_remove-cage-furnace-mot...
Q: What is squirrel-cage motor?
A: ( ′skwərl ¦kāj ′mōd·ər ) (electricity) An induction motor in which the secondary circuit consists of a squirrel-cage winding arranged in slots in the iron core. Read More »
Source: http://www.answers.com/topic/squirrel-cage-motor
Q: Why rotor of squirrel cage induction motor is skewed?
A: The squirrel cage is skewed so that the force applied to the rotor it continuous. If they were straight then the force would be jerky, as whole of the bar is cutting the magnetic field lines at the same time. With the bars skewed the amount... Read More »
Source: http://wiki.answers.com/Q/Why_are_the_slots_on_the_roto...
Q: What is a Squirrel Cage Motor?
A: An AC induction motor with a squirrel cage rotor is sometimes called a squirrel cage motor. In overall shape it is a cylinder mounted on a shaft. Internally it contains longitudinal conductive bars of aluminium or copper set into grooves an... Read More »
Source: http://answers.yahoo.com/question/index?qid=20070123060...
Q: How do I get the motor free from the squirrel cage?
A: Carolyn, Good question, I have been in the same pull your hair out predicament many time's while stuck in an attic or crawl space in somebodys house. There are different types of pulley pullers but fairly expensive and they don't always wor... Read More »
Source: http://en.allexperts.com/q/Heating-Air-Conditioning-696
induction motor
An electrical motor is such an electromechanical device which converts electrical energy into a mechanical energy. In case of three phase AC operation, most widely used motor is Three phase induction motor as this type of motor does not require any starting device or we can say they are self starting induction motor.
For better understanding the principle of three phase induction motor, the basic constructional feature of this motor must be known to us. This Motor consists of two major parts:
Stator: Stator of three phase induction motor is made up of numbers of slots to construct a 3 phase winding circuit which is connected to 3 phase AC source. The three phase winding are arranged in such a manner in the slots that they produce a rotating magnetic field after AC is given to them.
Rotor: Rotor of three phase induction motor consists of cylindrical laminated core with parallel slots that can carry conductors. Conductors are heavy copper or aluminum bars which fits in each slots & they are short circuited by the end rings. The slots are not exactly made parallel to the axis of the shaft but are slotted a little skewed because this arrangement reduces magnetic humming noise & can avoid stalling of motor.
Working of Three Phase Induction Motor
Production of Rotating Magnetic Field
The stator of the motor consists of overlapping winding offset by an electrical angle of 120°. When the primary winding or the stator is connected to a 3 phase AC source, it establishes a rotating magnetic field which rotates at the synchronous speed.
Secrets behind the rotation:
According to Faraday’s law an emf induced in any circuit is due to the rate of change of magnetic flux linkage through the circuit. As the rotor winding in an induction motor are either closed through an external resistance or directly shorted by end ring, and cut the stator rotating magnetic field, an emf is induced in the rotor copper bar and due to this emf a current flows through the rotor conductor.
Monday 12 May 2014
How Wind Turbines Generate Electricity
For centuries wind turbines have harnessed the force of wind to pump water and grind grain. Around 1910, the first wind turbines were built in Europe to produce electricity. Today, advances in technology and the need for renewable energy sources has made wind a fast growing source of electricity. Click on the video for an animation showing how wind turbines generate electricity.On top of each wind turbine is a box known as a nacelle. Attached to the nacelle are three propeller-like blades that connect to a rotor. Also on the nacelle is an anemometer to measure wind speed and direction. Click here for an inside view of a wind turbine.
The wind direction rotates the nacelle to face into the wind. The energy in the wind (called kinetic energy) turns the turbine blades around the rotor (creating mechanical energy).
The rotor connects to the main shaft, which turns inside the generator housing. Here, a magnetic rotor spins inside loops of cooper wire. This causes electrons inside the cooper to flow; creating electrical energy (what we call electricity in our daily lives).
The electricity generated then travels down large cables from the nacelle, through the tower, and into an underground cable. At wind farms, cables from different turbines take the electricity generated to a substation. Here, a step-up transformer again increases the electrical output.
A transmission line connects the electr
STK ALTERNATORS
STK WIND TURBINE ALTERNATORS
Permanent magnets frameless alternators for Direct Drive of wind turbines
The range of STK Permanent Magnet alternators, also called permanent magnet generators, addresses the applications of Wind Turbine generators, windmill alternators or windmill generators for small wind turbines, that is to say in low and medium power needing the highest power-to-weight ratio in Direct Drive without gear for matching cost-effective solutions.
Main characteristics of wind turbine alternators
- Rated power from 200 W up to 95 kW depending on size and rated speeds.
- Rated speeds from 80 RPM up to 1500 RPM.
- Six overall diameters from 145 mm up to 795 mm.
- Internal diameter from 56 mm up to 630 mm.
- Various available voltages up to 500 Vac.
- For environment and integration constraints, please request our STK handbooks for assembly
Assets of wind turbine alternators
- No speed multiplier, no gear
- No maintenance
- Highest power-to-weight ratio in Direct Drive
- High efficiency
- Simplification of mechanical design
- Easy mechanical interface
- Cost optimization
Characteristics of the range of wind turbine alternators
The range of AC frameless permanent magnet generators STK includes 6 sizes from 145 mm up to 800 mm available in four different lengths per size and two standard rated speeds. Their extremely compact design and high efficiency allow the use in direct drive in small wind turbines as wind turbine generators and windmill generators.
A part of the Jindal Group(Sangrur Industrial Corporation Ltd.), based in Sangrur, India, we been manufacturing, and now exporting, transformers with a rating ranging from 5 KVA to 2000 KVA upto 33 KV class. Led by a team of experienced engineering professionals, our transformers are manufactured under a comprehensive quality management system. Our state of the art manufacturing facilities, ensures that our customers get the best product available. The transformers are manufactured with internationally recognized standards such as
IEC - International Electronics Commission
ANSI - American National Standards Institute BS - British Standard IS - Indian Standard Today, It is one of the leading manufacturers of Oil Cooled Transformers, Current Transformers and Power & Distribution Transformers. The company manufacturers Power & Distribution Transformers using the most modern engineering concepts and high quality materials processed under expert supervision and rigid quality control. Transformers are designed for optimum efficiency while operating between 40% and 50% of full load by delicate proportioning of core and winding losses. By using CRGO silicon steel mitred cores and paper/polyester enamel covered copper conductors the units are made compact, resulting in lower losses, better regulation and longer life. Careful design of the core reduces noise level to the minimum. All routine tests as per IS, BS, ANSI and IEC are carried out by highly qualified technicians with calibrated precision-grade testing equipment on all the transformers. The company is looking forward to serve the customers with fine quality products. |
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