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In a hysteresis motor, the rotor must have retentivity.

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Answer : The rotor of a hysteresis motor is made of chrome steel.

Answer : Locked rotor current of a shaded pole motor is slightly more than full load current.

Description : Describe with neat sketch working of hysteresis motor.

Answer : Working: When stator is energized with single phase ac supply, rotating magnetic field is produced because of starting (auxiliary) and main windings, which remain in circuit permanently. The ... the principle of magnetic locking this motor either rotates at synchronous speed or not at all.

Answer : A hysteresis motor works on the principle of hysteresis loss.

Answer : The direction of rotation of an hysteresis motor is determined by position of shaded pole with respect to main pole.

Description : An electric motor in which both stator field and rotor rotates with same speed is called?

Answer : An electric motor in which both stator field and rotor rotates with same speed is called synchronous motor.

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Description : The rotor impedance of a slip ring induction motor is (0.1 + j0.6)Ohm/ ph . The resistance/ph to be inserted into rotor to get maximum torque at starting should be

Answer : The rotor impedance of a slip ring induction motor is (0.1 + j0.6)Ohm/ ph . The resistance/ph to be inserted into rotor to get maximum torque at starting should be 0.5 Ohm

Description : Ratio of the rotor reactance X to the rotor resistance R for a two-phase servo motor (A) is equal to that of a normal induction motor (B) is less than that of a normal induction motor (C) ... than that of a normal induction motor (D) may be less or greater than that of a normal induction motor

Answer : C

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Description : What is the rotor of a motor?

Answer : Rotor is the rotating or moving part in motor and generator.

Description : The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as?

Answer : The maximum constant load torque under which a synchronous motor will pull into synchronism at rated rotor supply voltage and frequency is known as pull-in torque.

Answer : As hysteresis motors are free from mechanical and magnetic vibrations therefore these are considered as suitable for sound equipment.

Description : In dc machines, the armature windings are placed on the rotor because of the necessity for  (1) electromechanical energy conversion (2) generation of voltage (3) commutation (4) development of torque

Answer : 3  Commutation

Description : Hysteresis is commonly found in ______ A) ferromagnetic materials B) ferroelectric materials C) both A and B D) none of these

Answer : Hysteresis is commonly found in ______ A) ferromagnetic materials B) ferroelectric materials C) both A and B D) none of these

Description : If the area of hysteresis loop of a material is large, the hysteresis loss in this material will be?

Answer : If the area of hysteresis loop of a material is large, the hysteresis loss in this material will be large.

Description : In a magnetic material hysteresis loss takes place primarily due to?

Answer : In a magnetic material hysteresis loss takes place primarily due to it high retentivity.

Description : What is magnetic hysteresis? What is the cause of hysteresis?

Answer : Magnetic hysteresis: When a magnetic material is subjected to cycle of magnetization, it is found that flux density (B) in the material lags behind applied magnetizing force (H). This ... the movement of orientation, due to which the flux density lags behind the magnetic field intensity.

Description : State the factors affecting hysteresis loss.

Answer : i) Flux density ii) Frequency iii) Volume of the magnetic material iv) Nature of magnetic material

Description : Explain the hysteresis loop of a magnetic material with neat diagram.

Answer : Hysteresis loop of magnetic material:  The circuit arrangement for plotting the hysteresis loop is shown in figure given below. The electromagnetic part consists of a coil wound on the iron ring ... one magnetic reversal is called hysteresis loop. Meaning of hysteresis is to lag behind.

Description : The term hysteresis is associated with (A) On-Off control (B) P-I control (C) Feed forward control (D) Ratio control

Answer : The term hysteresis is associated with On-Off control

Description : What is the difference between eddy current and hysteresis loss?

Answer : Loss occurred by magnetising and demagnetising process is called histerisis loss and the current flowed due to the magnetic field produced by the electric field applied is called eddy current losses

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Answer : The bearings used to support the rotor shafts are generally ball bearings.

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Answer : Salient pole rotor is use for low and medium speed prime movers.

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 : 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

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Description : The maximum torque which a synchronous motor will develop at rest for any angular position of the rotor, at rated stator supply voltage and frequency, is known as?

Description : Damper winding in a synchronous motor

Answer : Damper winding in a synchronous motor Serves to start the motor.

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 : In a 2 kW, 200 V, 1000 rpm. DC series motor the torque at full load was found to be 0.3 N -m. The torque at half full load in N -m is :

Answer : In a 2 kW, 200 V, 1000 rpm. DC series motor the torque at full load was found to be 0.3 N -m. The torque at half full load in N -m is : 0.075

Description : The function of a brush and commutator arrangement in a dc motor is to  (1) produce unidirectional torque (2) produce unidirectional current in the armature (3) help in changing the direction of rotation of the armature (4) reduce sparking

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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

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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

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Answer : In a differentially compounded D.C. motor, if shunt field suddenly opens the motor will first stop and then run in opposite direction as series motor.

Answer : Sparking, is discouraged in a D.C. motor because commutator gets damaged.

Answer : Sparking at the commutator of a D.C. motor may result in damage to commutator segments, damage to commutator insulation, increased power consumption.

Answer : In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to 25% of the previous value.

Answer : In case the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be less than 50%.

Answer : In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be more than full-load current.

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