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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.

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Answer :

Armature coil is short circuited by brushes when it lies along neutral axis.

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Answer :

If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will stop.

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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

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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

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227 views 1 answer
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 jointing problems (3) 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

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533 views 1 answer
Description :

In a synchronous machine, if the field flux axis ahead of the armature field axis in the direction of rotation, the machine is operating as  (1) synchronous motor (2) synchronous generator (3) asynchronous motor (4) asynchronous generator

Answer :

In a synchronous machine, if the field flux axis ahead of the armature field axis in the direction of rotation, the machine is operating as synchronous generator 

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368 views 1 answer
Description :

The armature current on symmetrical 3 phase short circuit of a synchronous machine (salient pole)  (A) has q -axis current only (B) has d -axis current only (C) has both d and q axis currents (D) cannot be divided between q and d axis currents

Answer :

The armature current on symmetrical 3 phase short circuit of a synchronous machine (salient pole) has d -axis current only

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Description :

Answer :

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

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Description :

Answer :

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

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Description :

Answer :

In a D.C. machine stray loss is the sum of iron loss and mechanical loss.

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112 views 1 answer
Description :

Answer :

To avoid formation of grooves in the commutator of a D.C. machine the brushes of opposite polarity should track each other.

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Description :

Answer :

Iron losses in a D.C. machine are independent of variations in load.

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Description :

Answer :

In a four-pole D.C. machine alternate poles are north and south.

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Description :

Answer :

In case of D.C. machine winding, number of commutator segments is equal to number of armature coils.

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421 views 1 answer
Description :

Explain concept of back emf in DC machine. State how it governs armature current. 

Answer :

Back emf: When the armature of DC machine rotates under the influence of driving torque, the armature conductors move in the magnetic field and cut it and hence emf is induced in them. The ... flow of armature current i.e. it automatically changes the armature current to meet load requirements.

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Description :

Answer :

Armature reaction of an unsaturated D.C. machine is crossmagnetising.

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Description :

A d.c. source has an open circuit voltage of 30 V and an internal resistance of 1.5 Ohm. A resistive load is connected to the source. Maximum power dissipated in the load is (A) 300 W (B) 150 W (C) 45 W (D) 20 W

Answer :

A d.c. source has an open circuit voltage of 30 V and an internal resistance of 1.5 Ohm. A resistive load is connected to the source. Maximum power dissipated in the load is 150 W

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180 views 1 answer
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.

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Description :

Answer :

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

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Description :

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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Description :

Answer :

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

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Description :

Answer :

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

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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

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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

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Description :

Why is the armature of DC generator laminated?

Answer :

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

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157 views 1 answer
Description :

Armature control of DC motor

Answer :

Armature control of DC motor

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Description :

A 36 slot, 4 -pole, dc machine has a simplex lap winding with two conductors per slot. The back pitch and front pitch adopted could be respectively

Answer :

A 36 slot, 4 -pole, dc machine has a simplex lap winding with two conductors per slot. The back pitch and front pitch adopted could be respectively 19,17

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Description :

In a dc machine, interpoles are used to  (1) neutralize the effect of armature reaction in the interpolar region (2) generate more induced emf in the armature (3) avoid interference of the armature flux with the main -field flux (4) reduce the demagnetizing effect of armature reaction

Answer :

In a dc machine, interpoles are used to neutralize the effect of armature reaction in the interpolar region

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Description :

The magnetic neutral plane shifts in a dc machine (A) in the direction of motion of motor (B) in the direction of motion of generator (C) due to increase in the field flux (D) cause reduction of flash over between commutator segments

Answer :

The magnetic neutral plane shifts in a dc machine in the direction of motion of generator

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Description :

Why poles of dc machine are laminated?

Answer :

Poles of DC machines are laminated to reduce the eddy current losses in the poles.

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55 views 1 answer
Description :

Answer :

Copper losses,iron losses,variable losses , constant losees

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159 views 1 answer
Description :

What is the percentage of stray losses in DC machine?

Answer :

Percentage of stray losses in DC machine is about 1 % .

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Description :

Brushes of DC machine are made up of ?

Answer :

Brushes of DC machine are made up of carbon.

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Description :

Answer :

Iron loss, copper loss and mechanical losses these are the losses in DC machine.

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Description :

Answer :

Armature reaction in a generator results in demagnetisation of leading pole tip and magnetisation of trailing pole tip.

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Description :

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.

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145 views 1 answer
Description :

Answer :

The commutator segments are connected to the armature conductors by means of copper lugs.

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134 views 1 answer
Description :

Answer :

The resistance of armature winding depends on length of conductor, cross-sectional area of the conductor, number of conductors.

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Description :

Answer :

In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called armature.

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116 views 1 answer
Description :

For a D.C. generator when the number of poles and the number of armature conductors is fixed, then which winding will give the higher e.m.f. ?

Answer :

Wave winding

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Description :

Answer :

In D.C. generators, current to the external circuit from armature is given through commutator commutator.

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142 views 1 answer
Description :

Answer :

A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be about 2 V.

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352 views 1 answer
Description :

Answer :

Eddy currents are induced in the pole shoes of a D.C. machine due to relative rotation between field and armature.

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155 views 1 answer
Description :

The induced e.m.f. in the armature conductors of a d.c. motor is?

Answer :

The induced e.m.f. in the armature conductors of a d.c. motor is sinusoidal.

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Description :

Answer :

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

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Description :

Describe the difference between an open circuit and a short circuit.

Answer :

Open circuit means the wire is cut meaning power will not flow and close circuit means wire is not cut and hence power will flow.Short circuit is the same as close circuit

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Description :

Answer :

It is required to measure the true open circuit e.m.f. of a battery. The best device is D.C. potentiometer.

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