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The armature voltage control of D.C. motor provides constant torque drive.

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Description : Armature control of DC motor

Answer : Armature control of DC motor

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 

Answer : The armature torque of the D.C. shunt motor is proportional to armature current.

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.

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 : What are the speed control methods of dc motor?

Answer : Field control of DC motor Armature control of DC motor

Description : Field control of DC motor

Answer : Field control of DC motor

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

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

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

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

Description : A 200 V DC machine supplies 20 A at 200 V as a generator. The armature resistance is 0.2 Ohm. If the machine is now operated as a motor at same terminal voltage and current but with the flux increased by 10%, the ratio of motor speed to generator speed is

Answer : A 200 V DC machine supplies 20 A at 200 V as a generator. The armature resistance is 0.2 Ohm. If the machine is now operated as a motor at same terminal voltage and current but with the flux increased by 10%, the ratio of motor speed to generator speed is 0.87

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 : The induced emf in the armature of a lap -wound four -pole dc machine having 100 armature conductors rotating at 600 rpm and with 1 Wb flux per pole is  (1) 1000V (2) 100V (3) 600V (4) 10,000V

Answer : The induced emf in the armature of a lap -wound four -pole dc machine having 100 armature conductors rotating at 600 rpm and with 1 Wb flux per pole is 1000V

Description : Aluminium is not used as winding wire for the armature of a dc machine because  (1) aluminium has low resistivity (2) a large winding space is taken by aluminium conductors and creates ... ) the thermal conductivity of aluminium is low (4) aluminium has low conductivity as compared to copper

Answer : Aluminium is not used as winding wire for the armature of a dc machine because  (2) a large winding space is taken by aluminium conductors and creates jointing problems (3) the thermal conductivity of aluminium is low (4) aluminium has low conductivity as compared to copper

Description : Why is the armature of DC generator laminated?

Answer : The armature of DC generator is laminated to reduce eddy current losses.

Answer : Series motor has the poorest speed control.

Answer : Speed control of a universal motor is achieved by varying field flux with tapped field windings, connecting rheostat in series, applying variable voltage by means of silicon controlled rectifier, applying variable voltage by means of variable auto-transformer.

Answer : The speed control of universal motor used for sewing machines is by varying the resistance.

Description : speed control methods of three phase induction motor?

Answer : Speed control of three phase induction motor

Answer : A sinusoidal voltage of 5 Hz is applied to the field of a shunt generator. The armature voltage wave will be of 5 Hz.

Answer : The current drawn by the armature of D.C. motor is directly proportional to the torque required.

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 a synchronous motor, the armature current has large values for high and low excitation.

Answer : The armature current of the synchronous motor has large values for low and high excitation.

Description : Explain the pulse width modulation technique for control of AC output voltage.

Description : What is the difference between a line voltage and low voltage control system?

Description : Explain the principle of ON-OFF control and phase control of AC voltage controller with suitable circuit and waveforms.

Answer : The integral cycle control (on-off control) and phase angle control are the two types of AC voltage controller. The principle of ON-OFF control: The on-off control is also called an integral cycle ... control. In phase control, the switch is on for some period of each cycle.  

Answer : Open circuited armature coil of a D.C. machine is identified by the scarring of the commutator segment to which open circuited coil is connected and indicated by a spark completely around the commutator.

Answer : The armature core of a D.C. generator is usually made of silicon steel.

Answer : The demagnetising component of armature reaction in a D.C. generator reduces generator e.m.f.

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 : The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is 0.5.

Description : Speed control of the motor using TRIAC

Answer : Speed control of the motor using TRIAC:  This basic phase triggering circuit uses the triac in series with the motor across an AC sinusoidal supply. The variable resistor, VR1 is used ... meaning that it may not trigger at the exact same point for each positive and negative half cycle.

Description : Identify the increasing order of voltage regulation of the following dc generators a same load :  (A) differential compound, shunt and under compound  (B) shunt, differential compound and ... C) under compound, shunt and differential compound  (D) shunt, under compound and differential compound

Answer : Identify the increasing order of voltage regulation of the following dc generators a same load : under compound, shunt and differential compound 

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.

Description : The speed of a D.C. motor can be controlled by varying  1. Its flux per pole 2. Resistance of armature circuit 3. Applied voltage 4. All of the above

Answer : The speed of a D.C. motor can be controlled by varying  1. Its flux per pole 2. Resistance of armature circuit 3. Applied voltage 4. All of the above

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

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 : The speed of a D.C. shunt motor can be increased by increasing the resistance in field circuit.

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

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

Answer : D.C. Series motor is generally preferred for cranes and hoists.

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 : 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.

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