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If a D.C. series motor is operated on A.C. supply, it will spark excessively, have poor efficiency, have poor power factor.

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Answer : A.C. series motor as compared to D.C. series motor has smaller brush width, less number of field turns, more number of armature turns, less air gap.

Answer : If a D.C. motor is connected across the A.C. supply it will burn due to heat produced in the field winding by eddy currents.

Description : State the modification to be done in dc series motor to work satisfactorily as ac series motor. State applications of ac series motor.

Answer : Modifications are necessary in a dc series motor so that it operates satisfactorily on ac supply. The modifications are as follows:  1) AC series motor is built with a few field turns as ... and grinders 5) High speed vacuum cleaners 6) Sewing machines 7) Food processors 8) Drilling machine 

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 : When a D.C. series motor is connected to A.C. supply, the power factor will be low because of high inductance of field and armature circuits.

Answer : In a A.C. series motor armature coils are usually connected to commutator through resistance.

Description : We connected a 35V dc supply to a resistance of 600 Ohm in series with an unknown resistance R.A. voltmeter having a resistance of 1.2 kOhm is connected across 600 Ohm resistance and read 5v. The value of resistance R will be

Answer : We connected a 35V dc supply to a resistance of 600 Ohm in series with an unknown resistance R.A. voltmeter having a resistance of 1.2 kOhm is connected across 600 Ohm resistance and read 5v. The value of resistance R will be 2.4 kOhm

Answer : The speed of a D.C. series motor is inversely proportional to the armature current.

Answer : A D.C. series motor is that which has its field winding consisting of thick wire and less turns.

Answer : The direction of rotation of a D.C. series motor can be changed by interchanging field terminals.

Description : Describe the reason of using dc series motor for electric trains.

Answer : Electric trains require an inverse torque speed characteristics for proper operation. That is a higher torque is required at start (when speed is nil or low) and as the train picks up ... torque - speed characteristics of DC series motors match, these motors are suitable for electric trains

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 speed of a 2-pole, 3-phase stepper motor operated by 1200 pulses/min (A) 100 rpm (B) 200 rpm (C) 400 rpm (D) 800 rpm

Answer : The speed of a 2-pole, 3-phase stepper motor operated by 1200 pulses/min 200 rpm

Answer : In A.C. series motor compensating winding is employed to reduce sparking at the brushes.

Description : Brake test on DC series motor

Answer : .embed-container { position: relative; padding-bottom: 56.25%; height: 0; overflow: hidden; max-width: 100%; } .embed-container iframe, .embed-container object, .embed-container embed { position: absolute; top: 0; left: 0; width: 100%; height: 100%; }

Description : What are the advantages of DC series motor?

Description : Why dc series motor should not be started at no load?

Description : Why a dc series motor has a high starting torque?

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

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

Description : Two 100W, 200V lamps are connected in series across a 200V supply. The total power consumed by each lamp will be in Watts

Answer : 4800

Answer : At the instant of starting when a D.C. motor is put on supply, it behaves like a low resistance circuit.

Answer : If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then the stator current will be zero.

Description : What will happen if the primary of a transformer is connected to D.C. supply?  (A) Transformer will operate with low efficiency (B) Transformer will operate with high efficiency (C) No effect (D) Transformer may start to smoke and burn 

Answer : What will happen if the primary of a transformer is connected to D.C. supply?  (A) Transformer will operate with low efficiency (B) Transformer will operate with high efficiency (C) No effect (D) Transformer may start to smoke and burn 

Description : A capacitor-start single phase induction motor is switched on to supply with its capacitor replaced by an inductor of equivalent reactance value. It will?

Answer : A capacitor-start single phase induction motor is switched on to supply with its capacitor replaced by an inductor of equivalent reactance value. It will not start at all.

Answer : The armature may burn if the back e.m.f. of a D.C. motor vanishes suddenly.

Description : In case of conductively compensated D.C. series motors, the compensating winding is provided?

Answer : In case of conductively compensated D.C. series motors, the compensating winding is provided in series with armature winding.

Answer : When two D.C. series motors are connected in parallel, the resultant speed is normal speed.

Description : Draw the waveform of three phase AC supply voltage.

Description : The SCR would be turned OFF by voltage reversal of applied anode-cathode ac supply frequency of A) 10 kHz B) 10 Hz C) 5 kHz D) 5 Hz 

Description :  An AC supply of 230 V is applied to a half-wave rectifier circuit through a transformer having primary to secondary turn’s ratio 12:1. The peak inverse voltage is A) 8.62 V B) 12 V C) 19.17 V D) 27.11 V 

Answer :  An AC supply of 230 V is applied to a half-wave rectifier circuit through a transformer having primary to secondary turn’s ratio 12:1. The peak inverse voltage is A) 8.62 V B) 12 V C) 19.17 V D) 27.11 V 

Description : Total instantaneous power supplied by a 3-phase ac supply to a balanced R-L load is

Answer : Total instantaneous power supplied by a 3-phase ac supply to a balanced R-L load is constant

Description : Why does a transformer only work with an AC supply?

Answer : The transformer work depends on the induction as main principle ,for that AC is the right means

Description : If a transformer is continuously operated the maximum temperature rise will occur in?

Answer : If a transformer is continuously operated the maximum temperature rise will occur in windings.

Description : Write two applications of D.C. series motor. 

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Answer : In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will remain unchanged.

Answer : As the load is increased the speed of D.C. shunt motor will reduce slightly.

Answer : Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be cumulatively compounded.

Answer : Cumulatively compounded D.C. motor will be suitable along with flywheel for intermittent light and heavy loads.

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.

Answer : If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor is to be derated by a factor recommended by manufacturer and select the next higher H.P. motor.

Answer : For a D.C. shunt motor if the excitation is changed torque will change but power will remain constant.

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 : If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses.

Answer : If the field of a D.C. shunt motor gets opened while motor is running the motor will attain dangerously high speed.

Answer : By looking at Commutator part of the motor, it can be easily confirmed that a particular motor is D.C. motor.

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.

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?

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