Description : In the illustrated device, the part labeled '1A' _________. EL-0001 A. are start and run windings for a single phase shaded pole induction motor B. is the stator for a polyphase induction ... armature for a squirrel cage rotor motor D. are direct current shunt field windings for a universal motor
Last Answer : Answer: B
Description : A characteristic of a wound-rotor induction motor, with a high resistance rotor winding, is _____________. A. low starting torque B. high starting torque C. high speed D. low starting voltage
Description : A shaded-pole motor is a ____________. A. synchronous motor B. three-phase induction motor C. compound-wound motor D. single-phase induction motor
Last Answer : Answer: D
Description : Why shaded-pole single phase induction motor does not need any special starting technique like capacitors and auxiliary winding etc.
Last Answer : Because it is inherently self started motor. The construction of the poles is such that they give a sweep to the magnetic flux and motor starts rotating.
Description : Which type of AC single-phase motor will also operate on direct current? A. Split-phase B. Series-wound C. Shaded-pole D. Repulsion-start
Description : A single-phase induction motor fails to start. The rotor is spun rapidly with the line switch closed. Having started by this method it is noted that the motor fluctuates between a very slow ... lies in the ______ A. starting winding B. centrifugal mechanism C. centrifugal switch D. running winding
Description : Why is the starting torque of a capacitor start induction motor high?
Last Answer : Ans: The capacitor C in the starting winding is so chosen that Is leads Im by 75 degree. Since the starting torque is directly proportional to Sin Ф, and it is quite high in capacitor-start induction motor.
Description : The variable resistance placed in the rotor circuit of a wound-rotor induction motor provides for __________. A. speed control B. frequency control C. voltage control D. use as a split-phase motor
Last Answer : Answer: A
Description : A single-phase induction motor will only start if you spin the rotor rapidly with the line switch closed. After starting, its speed fluctuates between very slow and half-speed. The problem ... in the ________. A. starting winding B. centrifugal mechanism C. centrifugal switch D. running winding
Description : In the illustration, the assembly labeled 2 is a ________. EL-0001 A. wound rotor and shaft for a single phase induction motor B. conduction rotor and shaft for a polyphase induction motor C. ... cage rotor and shaft for a polyphase motor D. squirrel cage rotor for a single phase induction motor
Last Answer : Answer: C
Description : Why is the starting torque of a resistance split-phase induction motor not high?
Last Answer : The starting torque is given as, Ts = K Im Is Sin Ф Where K = constant whose magnitude depends upon the design of the motor (i) The angle between Is and Im is small ... Im are not equal in magnitude, the rotating magnetic field is not uniform and the starting torque produced is small.
Description : In a 15 HP induction-type motor with a cage rotor, the current required at standstill to produce starting torque is approximately ____________. A. half the full load current B. equal to the full load current C. five times the full load current D. ten to twenty times the full load current
Description : Why do we use capacitor-start induction motors in applications requiring high starting torque in preference to repulsion induction motors?
Last Answer : Capacitors are easily available, cheaper and reliable. Repulsion-induction motors posses a special commutator and brushes that require maintenance. Most manufacturers have stopped making them.
Last Answer : Ans : Capacitors are easily available, cheaper and reliable. Repulsion-induction motors posses a special commutator and brushes that require maintenance. Most manufacturers have stopped making them.
Description : A single-phase induction motor starts, comes up to about 75% rated speed, slows down to a lower speed, and accelerates again. The problem is most likely in the ____________. A. starting winding B. running winding C. starting capacitor D. running centrifugal switch
Description : An 8 pole wound rotor induction motor operating on 60 Hz supply is driven at 1800 r.p.m. by a prime mover in the opposite direction of revolving magnetic field. The frequency of the rotor current is (a) 30 Hz (b) 60 Hz (c) 120 Hz (d) 180 Hz
Last Answer : 30 Hz As the frequency of the rotor is given by F= N*P/120 so from the above equation the frequency of the rotor current can be easily calculated i.e. 1800×8/120=30 Hence the required value of rotor frequency is 30 Hz
Description : A 6 pole 3-phase wound-rotor induction machine is driven by another machine at 1800 rpm. The rotor of the induction machine is connected to a 50Hz system. If the mechanical rotation of the rotor is in the same direction as the rotor winding flux rotation, then frequency of the stator voltage will be
Last Answer : A 6 pole 3-phase wound-rotor induction machine is driven by another machine at 1800 rpm. The rotor of the induction machine is connected to a 50Hz system. If the mechanical rotation of ... the same direction as the rotor winding flux rotation, then frequency of the stator voltage will be 140 Hz.
Description : How the starting winding produce rotation in a single phase resistance start induction motor?
Last Answer : The starting winding is highly resistive and the main winding is inductive. So the phase difference between the two currents becomes nearly 90 degree and hence the motor start as two phase motor.
Description : In a single phase induction motor driving a fan load, the reason for having a high resistance rotor is to achieve (A) low starting torque (B) quick acceleration (C) high efficiency (D) reduced size
Last Answer : In a single phase induction motor driving a fan load, the reason for having a high resistance rotor is to achieve quick acceleration
Description : The torque and current curves for a three-phase induction motor with a cage rotor, are shown in the illustration. Which of the following statements is true concerning the depicted curves? EL-0056 A. As slip ... D. If the motor is loaded to the point where 40% slip has resulted, it will stall.
Description : A four pole, 60 Hz, three-phase synchronous motor comes up to 1760 RPM when started as an induction motor. What is the percent slip after the rotor field is energized? A. 0 B. 1.1 C. 2.2 D. 3.3
Description : A 3-phase, 400 votts, 50 Hz, 100 KW, 4 pole squirrel cage induction motor with a rated slip of 2% will have a rotor speed of (A) 1500 rpm (B) 1470 rpm (C) 1530 rpm (D) 1570 rpm
Last Answer : Ans: B N = NS (1-S) and NS =120 f / p =120 x 50 /4 = 1500 rpm ∴N= 1500 (1-0.02) =1470 rpm
Description : The synchronous speed for a 3 phase 6-pole induction motor is 1200 rpm. If the number of poles is now reduced to 4 with the frequency remaining constant, the rotor speed with a slip of 5% will be _________. (A) 1690 rpm (B) 1750 rpm (C) 1500 rpm (D) 1710 rpm
Last Answer : (D) 1710 rpm
Description : The rotor frequency for a 3 phase 1000 RPM 6 pole induction motor with a slip of 0.04 is________Hz (A) 8 (B) 4 (C) 6 (D) 2
Last Answer : Ans: D Given: N=1000 rpm ; P= 6; s= 0.04; and f = NP/ 120 = 10006/120 = 50 Hz Rotor frequency fr=sf = 0.0450 = 2.0 Hz
Description : A balanced three-phase, 50 Hz voltage is applied to a 3 phase, 4 pole, induction motor. When the motor is delivering rated output, the slip is found to be 0.05. The speed of the rotor m.m.f. relative to the rotor structure is (A) 1500 r.p.m. (B) 1425 r.p.m. (C) 25 r.p.m. (D) 75 r.p.m.
Last Answer : (D) 75 r.p.m.
Description : The frequency of the rotor current in a 3 phase 50 Hz, 4 pole induction motor at full load speed is about (A) 50 Hz. (B) 20 Hz. (C) 2 Hz. (D) Zero.
Last Answer : (C) 2 Hz.
Description : Explain speed control method of 3 phase induction motor by the following methods: (1) Pole changing (2) Rotor resistance control (3) Stator voltage
Last Answer : 1) Pole Changing Method: Synchronous speed is given by, From the above equation of synchronous speed, it can be seen that synchronous speed (and hence, running speed) can ... in voltage and consequently the speed decreases and vice versa. Ultimately speed depends on the supply voltage.
Description : A characteristic of an induction motor with a low resistance rotor winding is _____________. A. high starting voltage B. high starting current C. high slippage D. low starting voltage
Description : The purpose of a cage rotor winding placed on the rotor of a synchronous motor is to _____________. A. provide excitation to the DC field B. start the machine as an induction motor C. contribute extra torque at synchronous speed D. prevent the machine from falling out of step
Description : what is the application of shaded pole induction motor?
Last Answer : Because of its small starting torque, it is generally used for small fans, toys, instruments, hair driers, tape recorder, advertising display, ventilators, electric clock etc.
Description : What is the principle of operation of shaded-pole induction motor?
Last Answer : A shaded-pole motor is basically a small single-phase squirrel cage motor in which the starting winding is composed of short-circuited copper ring (called shading coil) surrounding one-third of each pole ... rotating magnetic field. As a result, the rotor is set in motion due to induction principle.
Description : In a capacitor start single-phase induction motor, the capacitor is connected (A) in series with main winding. (B) in series with auxiliary winding. (C) in series with both the windings. (D) in parallel with auxiliary winding.
Last Answer : Ans: B To make single phase motor self start. We split the phases at 90 degree. Hence, motor behaves like a two phase motor.
Last Answer : The torque produced in induction type relay (shaded pole structure) is inversely proportional to the square of the current.
Description : What type of rotor is used in split-phase motors? A. Drum B. Salient pole C. Squirrel-cage D. Wound-rotor
Description : Which of the following statements is true concerning a polyphase synchronous propulsion motor? A. The motor is started as an induction motor. B. Resistance is gradually added to the rotor circuit. C. ... is held below the rated current. D. The field winding is energized for starting purposes only.
Description : A four-pole induction motor, operating on three-phase 60 cycle current will operate at approximately ___________. A. 850 RPM B. 1,150 RPM C. 1,750 RPM D. 3,550 RPM
Description : Reduction in the capacitance of a capacitor-start motor, results in reduced (A) Noise. (B) Speed. (C) Starting torque. (D) Armature reaction.
Last Answer : Ans: C Reduction in the capacitance reduces starting voltage, which results in reduced starting torque.
Description : If the centrifugal switch or relay used for cutting out the starting winding of a split-phase induction motor fails to open once the motor is in operation, the _____________. A. motor will overspeed B ... C. motor will immediately stall under load D. motor torque will be above normal at rated speed
Description : Reversing any two of the three rotor leads on a wound-rotor induction motor will _____________. A. increase motor performance B. decrease motor performance C. reverse the motor rotation D. have no effect on the direction of rotation or motor performance
Description : The speed of a wound-rotor induction motor _____________. A. will be fixed by the number of field poles B. can be varied by a rheostat-type control C. can only be synchronous speed at full load D. can only attain synchronous speed at no load
Description : Which of the following physical characteristics does a wound-rotor induction motor possess that a squirrel cage motor does not? A. Slip rings B. End rings C. A centrifugal switch D. End plates
Description : A motor using a rheostat in the motor circuit to vary the speed is called a ____________. A. squirrel-cage induction motor B. regenerative braking motor C. wound-rotor induction motor D. synchronous motor
Description : A motor which can conveniently be operated at lagging as well as leading power factors is the (A) squirrel cage induction motor. (B) wound rotor induction motor. (C) synchronous motor. (D) DC shunt motor.
Last Answer : (C) synchronous motor.
Description : Starting torque can be obtained in the case of a single phase induction motor with identical main and auxiliary windings by connecting: (1) A capacitor across the mains (2) A capacitor in ... with the auxiliary winding (4) Equal value capacitors in series with the main and the auxiliary windings
Last Answer : Starting torque can be obtained in the case of a single phase induction motor with identical main and auxiliary windings by connecting: A capacitor is series with the auxiliary winding.
Last Answer : Capacitor start motor has high torque in starting
Last Answer : Locked rotor current of a shaded pole motor is slightly more than full load current.
Description : The speed of a three-phase squirrel-cage induction-type motor operating in a fixed frequency system is varied by changing the _____________. A. number of phases to the motor B. number of stator poles C. locked rotor current D. resistance of the rotor winding
Last Answer : In a shaded pole single-phase motor, the revolving field is produced by the use of shading coils.
Description : Regarding an induction motor, the power developed by the rotor automatically adjusts itself to the _____________. A. power required to drive the load B. speed required to drive the load C. current flow in the motor stator D. torque developed by the rotating field
Description : The rotor frequency for a 3-phase 6-pole, 1000 r.p.m. induction motor with a slip of 0.04 is (a) 2 Hz (b) 4 Hz (c) 6 Hz (d) 8 Hz
Last Answer : 2hz is rotor frequency