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Brushes of DC machine are made up of ?

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Brushes of DC machine are made up of carbon.

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Description : From which material field coils of DC generator are made of?

Answer : Field coils of DC generator are usually made of copper.

Answer : Brushes of D.C. machines are made of carbon.

Description : In a DC motor, it is important to place the brushes along ______ A) Magnetic Neutral Axis B) Normal Geometric Axis C) Nominal Geometric Axis D) None of these

Answer : In a DC motor, it is important to place the brushes along Magnetic Neutral Axis

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 : 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 : 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

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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

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

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

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

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

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

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 : 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 : 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 : The rotor of a hysteresis motor is made of chrome steel.

Answer : The rapid wear of brushes takes place due to abrasion from dust, excessive spring pressure, rough commutator bars, high mica insulation between com-mutation bars.

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Answer : The number of brushes in a commutator depends on amount of current to be collected.

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