induction machines

FIGURE 13-1 Super-E, premium efficiency induction motor rated 10 hp, 1760 r/min, 460 V, 3-phase, 60 Hz. This totally-enclosed fan-cooled motor has a full-load current of 12.7 A, efficiency of 91.7%, and power factor of 81%. Other characteristics: no-load current: 5 A; locked rotor current: 85 A; locked rotor torque: 2.2 pu; breakdown torque: 3.3 pu; service factor 1.15; total weight: 90 kg; overall length including shaft: 491 mm; overall height: 279 mm. (Courtesy of Baldor Electric Company)

Theodore WildiElectrical Machines, Drives, and Power Systems, 6e

Copyright © 2006 by Sperika Enterprises and published by Pearson Education, Inc.

Upper Saddle River, New Jersey 07458All rights reserved.

FIGURE 14-4 Totally enclosed, fan-cooled, explosion-proof motor. Note the particularly rugged construction of this type of motor. (Courtesy of Brook Crompton-Parkinson Ltd)




FIGURE 13-2 Exploded view of the cage motor of Fig. 13.1, showing the stator, rotor, end-bells, cooling fan, ball bearings, and terminalbox. The fan blows air over the stator frame, which is ribbed to improve heat transfer. (Courtesy of Baldor Electric Company)




FIGURE 13-6 Elementary stator having terminals A, B, C connected to a 3-phase source (not shown). Currents flowing from line to neutral are considered to be positive.




FIGURE 13-9a Phase group 1 is composed of a single coil lodged in two slots. Phase group 2 is identical to phase group 1. The two coils are connected in series. In practice, a phase group usually consists of two or more staggered coils.




FIGURE 13-25 Stator winding of a 3-phase, 50 hp, 575 V, 60 Hz, 1764 r/min induction motor. The stator possesses 48 slots carrying 48 coils connected in wye. a. Each coil is composed of 5 turns of five No. 15 copper wires connected in parallel. The wires are covered with a high-temperature polyimide insulation. Five No. 15 wires in parallel is equivalent to one No. 8 wire. b. One coil side is threaded into slot 1 (say) and the other side goes into slot 12. The coil pitch is, therefore, from 1 to 12. c. Each coil side fills half a slot and is covered with a paper spacer so that it does not touch the second coil side placed in the same slot. Starting from the top, the photograph shows 3 empty and p p p p g p p g p p yuninsulated slots and 4 empty slots insulated with a composition paper liner. The remaining 10 slots each carry one coil side. d. A varnished cambric cloth, cut in the shape of a triangle, provides extra insulation between adjacent phase groups. (Courtesy of Services Électromécaniques Roberge)




FIGURE 13-22f The phase may be connected in wye or in delta, and three leads are brought out to the terminal box.




FIGURE 13-3a Die-cast aluminum squirrel-cage rotor with integral cooling fan. (Courtesy of Lab-Volt)




FIGURE 14-5 Typical torque-speed curves of NEMA Design B, C, and D motors. Each curve corresponds to the minimum NEMA values of locked-rotor torque, pull-up torque, and breakdown torque of a 3-phase, 1800 r/min, 10 hp, 60 Hz, squirrel-cage induction motor. The cross section of the respective rotors indicates the type of rotor bars used.




FIGURE 13-4b Close-up of the slip-ring end of the rotor. (Courtesy of Brook Crompton Parkinson Ltd)




FIGURE 13-4a Exploded view of a 5 hp, 1730 r/min, wound-rotor induction motor.




FIGURE 13-19 External resistors connected to the three slip-rings of a wound-rotor induction motor.




FIGURE 14-12 The electric train makes the round trip between Zermatt (1604 m) and Gornergrat (3089 m) in Switzerland. The drive is provided by four 3-phase, wound-rotor induction motors, rated 78 kW, 1470 r/m, 700 V, 50 Hz. Two aerial conductors constitute phases A and B, and the rails provide phase C. A toothed gear-wheel 573 mm in diameter engages a stationary rack on the roadbed to drive the train up and down the steep slopes. The speed can be varied from zero to 14.4 km/h by means of variable resistors in the rotor circuit. The rated thrust is 78 kN. (Courtesy of ABB)




FIGURE 13-31 This 17 t electric train is driven by a linear motor. The motor consists of a stationary rotor and a flat stator fixed to the undercarriage of the train. The rotor is the vertical aluminum plate mounted in the center of the track. The 3-tonne stator is energized by a 4.7 MVA electronic dc to ac inverter whose frequency can be varied from zero to 105 Hz. The motor develops a maximum thrust of 35 kN (7800 lb) and the top speed is 200 km/h. Direct-current power at 4 kV is fed into the inverter by means of a brush assembly in contact with 6 stationary dc busbars mounted on the left-hand side of the track.

Electromagnetic levitation is obtained by means of a superconducting electromagnet. The magnet is 1300 mm long, 600 mm wide, and 400 mm deep, and weighs 500 kg. The coils of the magnet are maintained at a temperature of 4 K by the forced circulation of liquid helium. The current density is 80 A/mm2, and the resulting flux density is 3 T. The vertical force of repulsion attains a maximum of 60 kN and the vertical gap between the magnet and the reacting metallic track varies from 100 mm to 300 mm depending on the current. (Courtesy of Siemens)




FIGURE 14-17 The water supply in the City of Stuttgart, Germany, is provided by a pipeline that is 1.6 m in diameter and 110 km long. The water is pumped from Lake Constance in the Alps. The pump in the background is driven by a wound-rotor induction motor rated at 3300 kW, 425 to 595 r/min, 5 kV, 50 Hz. The variable speed enables the water supply to be varied according to the needs of the city. The enclosed motor housing seen in the foreground contains an air/water heat exchanger that uses the 5°C water for cooling purposes. During start-up, liquid rheostats are connected to the slip-rings, but when the motor is up to speed the slip-rings are connected to an electronic

hi h f d h b k i h li ( f )converter which feeds the rotor power back into the line. (Courtesy of Siemens)




FIGURE 13-40 This Middelgrunden Offshore Wind Farm is located just outside Copenhagen Harbour, in Denmark. It consists of twenty 2 MW turbines yeilding a total output of 40 MW. The blades are 38 m long, revolving at a hub height of 64 m. The twenty turbines are equipped with squirrel-cage induction generators that together produce a guaranteed minimum of 89 000 MW h per year. (Photo © BONUS Energy A/S)




FIGURE 13-5a Moving magnet cutting across a conducting ladder.

FIGURE 13-5b Ladder bent upon itself to form a squirrel cage.




FIGURE 13-6 Elementary stator having terminals A, B, C connected to a 3-phase source (not shown). Currents flowing from line to neutral are considered to be positive.




FIGURE 13-7 Instantaneous values of currents and position of the flux in Fig. 13.6.




FIGURE 13-8a Flux pattern at instant 1.




FIGURE 13-8b Flux pattern at instant 2.




FIGURE 13-8c Flux pattern at instant 3.




FIGURE 13-8d Flux pattern at instant 4.




FIGURE 13-8e Flux pattern at instant 5.




FIGURE 13-8f Flux pattern at instant 6.




FIGURE 13-10a Phase A of a 4-pole stator.

The same scheme as above, with phases B and C also shown.




FIGURE 13-11 An 8-pole stator.




FIGURE 13-15 Active power flow in a 3-phase induction motor.




FIGURE 13-17 Typical torque-speed curve of a 3-phase squirrel-cage induction motor.




FIGURE 15-1 Equivalent circuit of a wound-rotor induction motor at standstill.

FIGURE 15-2 Approximation of the equivalent circuit is acceptable for motors above 2 hp.




FIGURE 15-3 Equivalent circuit of a wound-rotor motor when it is running at a slip s. The frequency of the voltages and currents in thestator is f. But the frequency of the voltages and currents in the rotor is sf.

FIGURE 15-6 Equivalent circuit of a wound-rotor motor referred to the primary (stator) side.




FIGURE 15-6 Equivalent circuit of a wound-rotor motor referred to the primary (stator) side.

FIGURE 15-7 The primary and secondary leakage reactances x1 and x2 are combined to form an equivalent total leakage reactance x.




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induction machines

Documents

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rotor induction

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power systems

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