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Series motor should not be started on no-load.

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Description : Why dc series motor should not be started at 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

Last 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

Description : A no-load test is performed on a transformer to determine?

Last Answer : A no-load test is performed on a transformer to determine magnetizing current and loss.

Description : Even at no-load, a transformer draws current from the mains. Why?

Description : In a battery, the difference between the no-load voltage and the measured voltage output is called ________ A) Internal voltage B) Internal resistance C) External resistance D) All the above

Last Answer : In a battery, the difference between the no-load voltage and the measured voltage output is called Internal resistance

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

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

Description : D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select the?

Last Answer : D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select the compound motor.

Description : D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the?

Last Answer : D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the series motor.

Last 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.

Description : The d.c. series motor should never be switched on at no load because?

Last Answer : The d.c. series motor should never be switched on at no load because the speed becomes dangerously high.

Description : The d.c. series motor should always be started with load because (A) at no load, it will rotate at dangerously high speed. (B) it will fail to start. (C) it will not develop high starting torque. (D) all are true.

Last Answer : (A) at no load, it will rotate at dangerously high speed.

Description : A d.c. motor can be looked upon as d.c. generator with the power flow?

Last Answer : A d.c. motor can be looked upon as d.c. generator with the power flow reversed.

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

Last 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 when a DC shunt motor is started with a load?

Last Answer : Starting current will be very high so motor will take more current from supply. It may damage the armature winding.

Description : Explain the necessity of starter for D.C. motor. State various types of D.C. motor starter. 

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

Last 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 : In a d.c. motor, the mechanical output power actually comes from?

Last Answer : In a d.c. motor, the mechanical output power actually comes from electrical input power.

Description : The mechanical power developed by the armature of a d.c. motor is equal to?

Last Answer : The mechanical power developed by the armature of a d.c. motor is equal to armature current multiplied by back e.m.f.

Description : The Eb/V ratio of a d.c. motor is an indication of its?

Last Answer : The Eb/V ratio of a d.c. motor is an indication of its efficiency.

Description : The normal value of the armature resistance of a d.c. motor is?

Last Answer : The normal value of the armature resistance of a d.c. motor is 0.5.

Description : The counter e.m.f. of a d.c. motor?

Last Answer : The counter e.m.f. of a d.c. motor helps in energy conversion.

Description : In a d.c. motor, unidirectional torque is produced with the help of

Last Answer : Commutator provides unidirectional torque and pulsating dc

Description : In DC motor iron losses are occurred in?

Last Answer : In DC motor iron losses are occurred in the armature.

Last Answer : Series motor has got maximum self relieving property.

Last Answer : When the armature of a D.C. motor rotates, e.m.f. induced is back e.m.f.

Last Answer : Shunt motors,  Series motors, Compound motors

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Last Answer : Torque developed by a D.C. motor depends upon magnetic field, active length of the conductor, current flow through the conductors, number of conductors, radius of armature.

Last Answer : If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will increase.

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

Last 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.

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

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

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

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

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

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 :

Last 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

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

Description : A d.c. shunt motor runs at no load speed of 1140 r.p.m. At full load armature reaction weakens the main flux by 5%. Whereas the armature circuit voltage drops by 10%. The full load speed of the motor is (a) 1200 r.p.m. (b) 1080 r.p.m. (c) 1040 r.p.m. (d) 1000 r.p.m.

Description : Between no-load and full-load, .......... motor develops the least torque.

Last Answer : series motor

Description : The torque-speed characteristics of an a.c. operated universal motor has a ______characteristic and it______ be started under no-load condition. (A) inverse, can (B) nearly inverse, can (C) inverse, cannot (D) nearly inverse, cannot

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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

Last 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 : A three-phase synchronous motor connected to ac mains is running at full load and unity power factor. lf its shaft load is reduced by half and field current is held constant then its new power factor will be

Last Answer : Leading

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

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

Last Answer : In case of a reluctance motor, when the load is increased so that it cannot maintain synchronous speed the motor will run as induction motor.

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

Last 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?

Last 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.

Last 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?

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

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