# Open circuited armature coil of a D.C. machine is?

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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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

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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

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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

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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

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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.

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

Description : Armature control of DC motor

Last Answer : Armature control of DC motor

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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

Last 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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Description : Why poles of dc machine are laminated?

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

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Last 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 : 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

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

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

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

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Description : What is the effect of armature reaction? A) Demagnetization of the main field B) Demagnetization of the brushes C) Cross-magnetization of the brushes D) None of these

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Description : The armature reaction in a synchronous generator supplying leading power factor load is (A) magnetizing (B) demagnetizing (C) demagnetizing and cross-magnetizing (D) magnetizing and cross-magnetizing

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

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

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