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Iron loss, copper loss and mechanical losses these are the losses in DC machine.
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Description : What is the percentage of stray losses in DC machine?

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

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

Answer : Copper losses,iron losses,variable losses , constant losees

Description : In DC motor iron losses are occurred in?

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

Description : Why poles of dc machine are laminated?

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

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

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

Description : Brushes of DC machine are made up of ?

Answer : Brushes of DC machine are made up of carbon.

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.

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 : 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 : 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

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

Answer : In a D.C. generator, the iron losses mainly take place in armature rotor.

Answer : The total losses in a well designed D.C. generator of 10 kW will be nearly 500 W.

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

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

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

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

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.

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Answer : A

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Answer : In case of D.C. machines, mechanical losses are primary function of speed.

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Answer : Reduction in core losses and increase in permeability are obtained with transformer employing core built-up of laminations of cold rolled grain oriented steel.

Description : Losses which occur in rotating electric machines and do not occur in transformers are?

Answer : Friction losses windage losses 

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Answer : In a given transformer for a given applied voltage, losses which remain constant irrespective of load changes are hysteresis and eddy current losses.

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

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

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