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

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Answer : Series motor should not be started on no-load.

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

Description : Why does the speed of a DC shunt motor decrease as the load increases?

Answer : Because if the load is increasing then the torque must also be increase. If not then the speed of motor will decrease.

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 

Description : A 240 V, dc shunt motor draws 15 A while supplying the rated load at a speed of 80 rad/s. The armature resistance is 0.5 W and the field winding resistance is 80 W. The net Voltage across armature resistance at the time of plugging will be

Answer : A 240 V, dc shunt motor draws 15 A while supplying the rated load at a speed of 80 rad/s. The armature resistance is 0.5 W and the field winding resistance is 80 W. The net Voltage across armature resistance at the time of plugging will be 474 V

Description : What are the advantages of DC series motor?

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 : 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

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

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 : If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens this will make armature to take heavy current, possibly burning it.

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

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

Description : DC series motor should never be started at no-load. Justify. 

Answer : At no load the field current (which is also the armature current) is very small and hence the useful air-gap field flux. Also the torque is very small.  As N ∝ 1/Ф the speed rises to ... on the rotating parts they may get damaged. Hence DC series motor should never be started on no-load.

Description : The no-load speed of a single-phase SCR bridge converter fed separately excited dc motor operating at a firing delay angle, α and flux, Φ (A) directly proportional to α and Φ (B) ... proportional to α and inversely proportional to Φ (D) directly proportional to Φ and inversely proportional to α

Answer : The no-load speed of a single-phase SCR bridge converter fed separately excited dc motor operating at a firing delay angle, α and flux, Φ directly proportional to α and inversely proportional to Φ

Answer : Series capacitors on transmission lines are of little use when the load VAR requirement is small.

Description : Explain series switching control of AC load. Single phase resistance load - Integral half cycle control Phase control - Resistance load

Description : A 3 -phase, fully controlled, converter is feeding power into a DC load at a constant current of 150 A, the rms value of the current flowing through each thyristor of the converter is

Answer : A 3 -phase, fully controlled, converter is feeding power into a DC load at a constant current of 150 A, the rms value of the current flowing through each thyristor of the converter is 150/√3

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 : 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.

Description : Explain with neat circuit diagrams the procedures to perform no load and blocked rotor tests on three phase induction motor.

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 : A DC voltage source is connected across a series RLC circuit. Under steady-state conditions, the applied DC voltage drops entirely across the

Answer : A DC voltage source is connected across a series RLC circuit. Under steady-state conditions, the applied DC voltage drops entirely across the C only

Description : The synchronous motor which works on leading power factor and does not drive any mechanical load is called?

Answer : The synchronous motor which works on leading power factor and does not drive any mechanical load is called synchronous condenser.

Description : Why DC motor is used for traction?

Description : In a 4-pole wave winding connected dc motor, the cross-magnetizing AT/pole for a brush shift of θ radians (A) Armature amp-conductors × (θ/360o) (B) Armature amp-turns × (θ/360o) (C) Armature amp-conductors × (1/4 - θ/360o) (D) Armature amp-conductors × (1/8 - θ/360o)

Answer : In a 4-pole wave winding connected dc motor, the cross-magnetizing AT/pole for a brush shift of θ radians Armature amp-conductors × (1/8 - θ/360o)

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

Answer : The applications of D.C. series motor: 1. Cranes 2. Hoists 3. Trolley and cars 4. Conveyors 5. For traction work i.e. electric locomotives 6. Elevator 7. Air compressor

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

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

Description : State at least one function and the material used for the following parts of DC Motor.

Answer : Part Function Material Yoke -Provides mechanical support for poles -Acts as protecting cover for machine -Provides path for magnetic flux Cast Iron OR Cast Steel Field Winding - ... Pole core  Provides mechanical support to field winding. Cast Iron OR Cast Steel

Description : A 200 V dc shunt motor is running at 1000 rpm and drawing a current of 10 A. Its armature winding resistance is 2 Ohm. It. is braked by plugging. The resistance to be connected in series with armature to restrict armature current to 10 A, is

Answer : A 200 V dc shunt motor is running at 1000 rpm and drawing a current of 10 A. Its armature winding resistance is 2 Ohm. It. is braked by plugging. The resistance to be connected in series with armature to restrict armature current to 10 A, is 36 Ohm

Description : The effect of increasing load on a synchronous motor running with normal excitation is (A) Increase both its Ia and power factor. (B) Decrease Ia, but increase power factor. (C) Increase Ia, but decrease power factor (D) Decrease both Ia and power factor.

Answer : The effect of increasing load on a synchronous motor running with normal excitation is Increase Ia, but decrease power factor

Answer : For the same H.P. rating and full load speed, following motor has poor starting torque differentially compounded.

Answer : The speed/load characteristics of a universal motor is same as that of D.C. series motor.

Answer : A synchronous motor running with normal excitation adjusts to load increases essentially by increase in armature current.

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 : The coupling angle or load angle of synchronous motor is defined as the angle between the rotor and the stator poles of opposite polarity.

Description : If the load of the normally excited synchronous motor is increased the power factor will?

Answer : If the load of the normally excited synchronous motor is increased the power factor will become lagging.

Description : In a synchronous motor which losses varies with load?

Answer : In a synchronous motor, copper losses varies with load.

Description : The synchronous motor will develop maximum power when the load angle is?

Answer : The synchronous motor will develop maximum power when the load angle is 900.

Description : In synchronous motor, does the winding losses vary with load?

Answer : No, in the synchronous motor the winding losses do not vary with load.

Description : As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit?

Answer : As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit a resistance is connected in series with armature.

Answer : The speed of a D.C. shunt motor more than its full-load speed can be obtained by decreasing the field current.

Description : If field current is decreased in shunt dc motor, the speed of the motor (a) remains same. (b) increases. (c) decreases. (d) none of the above.

Answer : increases

Description : What would happen if a DC motor was supplied with AC ?

Answer : With three phase induction motor, humming and not rotate, but if single phase universal motor like air blower, home mixture, motor run on constant speed..speed variation not possible...

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