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why induction motor is called rotating transformer?

1 Answer

Induction motor works on same principal as transformers work ie faradays law of electromagnetic induction. ie IM called as rotating transformer 

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Description : The slip of 400 V, three phase, 4 -pole induction motor when rotating at 1440 rpm is 

Answer : The slip of 400 V, three phase, 4 -pole induction motor when rotating at 1440 rpm is 4 percent

Description : A 3-phase, 4-pole, 50Hz induction motor runs at a speed of 1440 rpm. The rotating field produced by the rotor rotates at a speed of ________ rpm with respect to stator field. (A) 1500 (B) 0 (C) 1440 (D) 60

Answer : 0

Description : what is mean by rotating transformer ?

Answer : Induction motor is a rotating transformer

Description : Explain how in a 3 phase induction motor to a rotating magnetic field is developed. 

Answer : Production of Rotating Magnetic Field in Three-phase Induction Motor: In three-phase induction motor, the three-phase stator windings are displaced in space by 120° and their three-phase currents are displaced ... time by 120°. Such fluxes give rise to the resultant rotating magnetic field.

Description : Define rotating magnetic field of an induction motor. 

Answer : Rotating magnetic field of an induction motor: A rotating magnetic field is a magnetic field that has moving polarities in which its opposite poles rotate about a central point or axis.

Description : A 4-pole induction motor, supplied by a slightly unbalanced three-phase 50 Hz source, is rotating at 1440 rpm. The electrical frequency in Hz of the induced negative sequence current in the rotor is  (A) 100 (B) 98 (C) 52 (D) 48

Answer : A 4-pole induction motor, supplied by a slightly unbalanced three-phase 50 Hz source, is rotating at 1440 rpm. The electrical frequency in Hz of the induced negative sequence current in the rotor is 98 

Answer : The speed of the rotating magnetic field in an induction motor is known as the synchronous speed.

Description : Split phase induction motor

Answer : Split phase induction motor : There are two windings used in split phase induction motor. It is a type of single-phase induction motor. There are two winding one is called main winding and ... motor have low starting torque it is used for small fans, blowers, centrifugal pumps, grinders etc.

Description : The starting torque of a V/f controlled inverter-fed 3-phase induction motor operating at 25 Hz as compared with the same motor operating at 50 Hz is (A) more (B) double (C) equal (D) less 

Description : In slip-energy recovery scheme of converter-fed 3-phase induction motor, super synchronous speeds are possible by (A) injecting voltage into the stator (B) injecting voltage into the rotor (C) extracting voltage from the stator (D) extracting voltage from the rotor. 

Description : A 400 V, 50 Hz 30 hp, three-phase induction motor is drawing 50 A current at 0.8 power factor lagging. The stator and rotor copper losses are 1.5 kW and 900 W respectively. The friction and windage losses are 1050 W and the ... the motor will be (A) 23.06 kW (B) 24.11 kW (C) 25.01 kW (D) 26.21 kW

Answer : A 400 V, 50 Hz 30 hp, three-phase induction motor is drawing 50 A current at 0.8 power factor lagging. The stator and rotor copper losses are 1.5 kW and 900 W respectively. The friction and windage losses are 1050 W and the core losses are 1200 W. The air-gap power of the motor will be 25.01 kW

Description : The locked rotor current in a 3-phase, star connected 15 , kW 4 , pole 230 V , 50 Hz induction motor at rated conditions is 50 A. Neglecting losses and magnetizing current, the approximate locked rotor line current drawn when the motor ... Hz supply is  (A) 58.5 A (B) 45.0 A (C) 42.7 A (D) 55.6 A

Answer : The locked rotor current in a 3-phase, star connected 15 , kW 4 , pole 230 V , 50 Hz induction motor at rated conditions is 50 A. Neglecting losses and magnetizing current, the approximate locked rotor line current drawn when the motor is connected to a 236 , V 57 Hz supply is 45.0 A 

Description : In a double squirrel cage induction motor, good starting torque is produced as (A) Large current flows through the outer high resistance winding. (B) Large current flows through the inner high ... the outer high resistance winding. (D) Large current flows through the inner low resistance winding.

Answer : In a double squirrel cage induction motor, good starting torque is produced as Large current flows through the outer high resistance winding.

Description : A change of 4% in the supply voltage to an induction motor will produce a change of approximately

Answer : A change of 4% in the supply voltage to an induction motor will produce a change of approximately 8% in the rotor torque

Description : In an induction motor if the flux density is reduced to one-half, of its normal value then the torque will  (1) reduce to one-half (2) reduce to one-fourth (3) remain unchanged (4) increase four times

Answer : In an induction motor if the flux density is reduced.to one-half, of its normal value then the torque will reduce to one-fourth

Description : The speed of a three-phase induction motor is controlled by variable voltage variable frequency control (i.e. keeping V/f constant). As the frequency is reduced, the slip at maximum torque  (1) Decreases (2) Increases (3) Remains constant (4) None of the above

Answer : The speed of a three-phase induction motor is controlled by variable voltage variable frequency control (i.e. keeping V/f constant). As the frequency is reduced, the slip at maximum torque Increases 

Description : Slip test is performed to determine :  (A) Slip in an induction motor  (B) Xd and Xq in a salient pole alternator  (C) Synchronous impedance in an alternator  (D) Positive and negative sequence impedances of an alternator

Answer : Slip test is performed to determine :  Xd and Xq in a salient pole alternator 

Description : Torque developed by a three-phase, 400V, induction motor is 100 N -m. If the applied voltage is reduced to 200-V, the d'veloped torque will be

Answer : Torque developed by a three-phase, 400V, induction motor is 100 N -m. If the applied voltage is reduced to 200-V, the d'veloped torque will be 25 N -m

Description : A 400 V, 50 Hz three-phase induction motor rotates at 1440 rpm on full -load. The motor is wound for

Answer : A 400 V, 50 Hz three-phase induction motor rotates at 1440 rpm on full -load. The motor is wound for 4 poles

Description : In a split-phase induction motor, the resistance/reactance ratios of windings are such that (A) current in the auxiliary winding leads the current in the main winding (B) current in the ... (C) both windings develop the same starting torque (D) both windings develop high starting current

Answer : In a split-phase induction motor, the resistance/reactance ratios of windings are such that current in the auxiliary winding leads the current in the main winding

Description : In a single-phase induction motor when the rotor is stationary and voltage is applied to the stator, then (A) the flux is constant (B) the flux first decreases and then increases in ... increases and decreases in the opposite direction with the same magnitude (D) current flows through the rotor

Answer : In a single-phase induction motor when the rotor is stationary and voltage is applied to the stator, then the flux first decreases and then increases in the same direction

Description : An 8-pole, 50Hz, three-phase induction motor is running at 705rpm and has a rotor copper loss of 5kW. Its rotor input is (A) 5.06 kW (B) 0.3 kW (C) 100 kW (D) 83.33 kW

Answer : An 8-pole, 50Hz, three-phase induction motor is running at 705rpm and has a rotor copper loss of 5kW. Its rotor input is 83.33 kW

Description : The torque developed by any 3-phase induction motor at 0.8 p.u. slip is (A) Full-load torque (B) unstable torque (C) starting torque (D) break down

Answer : The torque developed by any 3-phase induction motor at 0.8 p.u. slip is unstable torque

Description : In a 3-phase slip-ring induction motor, the slip at some speed is 0.05. The speed is reduced by inserting an external resistance in the rotor circuit and the slip is 0.15. If the rotor winding resistance per phase is 0.2 Ω, the external resistance is (A) 0.2 Ω (B) 0.3 Ω (C) 0.4 Ω (D) 0.5 Ω

Answer : In a 3-phase slip-ring induction motor, the slip at some speed is 0.05. The speed is reduced by inserting an external resistance in the rotor circuit and the slip is 0.15. If the rotor winding resistance per phase is 0.2 Ω, the external resistance is 0.3 Ω

Description : The rotor winding of a three phase wound rotor induction motor is equipped with a three phase diode rectifier connected to the slip rings and rectifier output is connected with chopper drive. Compared to ... B) Maintains the motor rating as such C) Derates the motor D) None of the above 

Answer : If starting winding of a single-phase induction motor is left in the circuit, it will draw excessive current and overheat.

Answer : If a single phase induction motor runs slower than normal, the most likely defect is worn bearings.

Answer : The rotor slots, in an induction motor, are usually not quite parallel to the shaft because it helps in reducing the tendency of the rotor teeth to remain under the stator teeth.

Answer : Speed torque characteristic of a repulsion induction motor is similar to that of a D.C. compound motor.

Description : How is a three phase cage induction motor self starting?

Answer : Any type of induction motor is self starting. Because the reason for torqe production require two flux displaced by some angle theta.If theta is constant with time then torqe will be constant;if ... torqe also pulsating. In induction motor this angle theta is not pulsating.so it is self starting 

Description : How does a single phase induction motor work?

Answer : As we know that single phase induction is not self started because for self started we require atleast two revolving field but single phase induction motor has only one. So we provide extra ... 1phase IM classified as split phase IM, capacitor start capacitor run, capacitor start induction run.

Description : Is induction motor is self starting?

Answer : Single phase induction motor is not self starting. Three phase induction motor is self starting.

Description : What is the definition of induction motor?

Answer : its working on magnetic base made by coils and its work with 1 phase or 3 phase ac or dc supply

Description : What is the function of induction motor?

Answer : while you give supply to motor its motor run on magnet base 

Description : At which time power factor of the induction motor is low?

Answer : The power factor of the inducction motor is low at the time of starting as compare to while the induction motor is running.

Description : What is mean by plugging in three phase induction motor?

Answer : Plugging in three-phase induction motor means interchanging of any two phases of a stator for quick stopping.

Description : explain the working of single phase induction motor.

Answer : Stator has two winding namely main winding and auxiliary winding.when single phase ac supply is given to the motor,its produces alternating field.this field cut by a cage rotor.so some emf ... due to this emf,rotor flux produced.the interaction between two fluxes produce torque.so rotor rotates.

Answer : Capacitor start motor has high torque in starting

Answer : Induction motor is a AC motor it is also known as asynchronous motor .

Answer : if induction motor rotates exceed than its synchronous speed, it acts as a generator.

Description : Induction motor

Answer : Induction Motor Inductor is a coil of wire which possess the property of inductance. Inductance is the property of an electric conductor which generate electromotive force (EMF ... motor are classified as slip ring induction motor and squirrel cage induction motor.

Description : Single Phase Induction Motor

Answer : Single Phase Induction Motor Single phase induction motor is mostly used in home, office, shop and many single phase appliances like pumps,  ... torque and silent operation. It is uses where silent operation is required.

Description : Types of three phase induction motor rotor

Answer : Types of three phase induction motor rotorSquirrel cage rotor : There are two types of three phase induction motor rotor one is squirrel cage rotor and second is wound rotor. About 80 to ... control of three phase induction motor via rotor resistance control method is possible with this rotor.

Description : Stator Voltage Control of three phase induction motor

Answer : Stator Voltage Control of three phase induction motor

Description : speed control methods of three phase induction motor?

Answer : Speed control of three phase induction motor

Description : UNIT 1 fundamentals of AC rotating machine Contents 1.1 Introduction 1.2 Advantages 1.3 Parts of AC machines 1.4 Synchronous speed 1.5 AC winding 1.6 Winding factor ( ... alternator or generator 1.9 Numericals 1.10 Harmonic 1.11 Slot harmonics 1.12 Harmonics minimization

Answer : 1.2 Advantages: In practices most of alternator have rotating magnetic field type construction with stationary armature due to following reason. The generation level of AC voltage may be in the range ... at high speed. Only two Slip rings are required to excited the field by AC supply.

Description : A rotating electrical machine its self-inductances of both the stator and the rotor windings, independent of the rotor position will be definitely not develop  (A) starting torque (B) synchronizing torque (C) hysteresis torque (D) reluctance torque

Answer : A rotating electrical machine its self-inductances of both the stator and the rotor windings, independent of the rotor position will be definitely not develop synchronizing torque

Description : In an induction type energy meter, the steady speed attained by the rotating disc is  1. Proportional to the deflecting torque. 2. Proportional to the resistance of the path of eddy currents. 3. ... 4. Inversely proportional to the square of brake magnet flux.  Which of the above are correct ?

Answer : In an induction type energy meter, the steady speed attained by the rotating disc is 1. Proportional to the deflecting torque. 2. Proportional to the resistance of the path of eddy currents. 3. Inversely proportional to ... brake magnet flux. Which of the above are correct ? 1, 2, 3 and 4 

Description : Prepare troubleshooting chart for transformer as per IS- 10028-1981 (4 trouble) and Induction motor (4 troubles). 

Answer : Troubleshooting chart for I.M. :-  Sr.No Type of fault/abnormal conditions/Troubles Causes Remedies 1 Motor fails to start or not accelerate (Faults in starting supply ... 1.Unequal terminal voltage. 2. Single phase operation 3.Unbalanced voltage Rectify the Cause

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