1 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 : 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

Answer : It is the wire wound around a aluminium metal it is found commonly in transformers or motors

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

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

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.

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

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

Answer : Wave winding is composed of that even number which is exact multiple of poles + 2.

Answer : Lap winding is composed of any even number of conductors.

Answer : In D.C. generators, lap winding is used for low voltage, high current.

Answer : In the case of lap winding resultant pitch is difference of front and back pitches.

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

Answer : In lap winding, the number of brushes is always same as the number of poles.

Description : Write any two factors on which earth resistance depends.

Answer : Factors on which earth resistance depends: (1) The shape and material used for the electrode (2) Depth of the electrode in the ground. (3) The specific resistance of the soil around the electrode (4) Moisture content in the soil. (5) Nature of soil 

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 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

Description : The running winding of a single phase motor on testing with meggar is found to be ground. Most probable location of the ground will be?

Answer : The running winding of a single phase motor on testing with meggar is found to be ground. Most probable location of the ground will be at the slot edge where coil enters or comes out of the slot.

Answer : The critical resistance of the D.C. generator is the resistance of field.

Answer : In a D.C. generator, the critical resistance refers to the resistance of field.

Description : Define armature reaction in an alternator. Explain the effect of armature reaction at various P.F. of loads of alternator.

Answer : Armature Reaction: The effect of armature flux on main flux is called as armature reaction.  Armature Reaction at Various Power Factors: When armature is loaded, the armature flux modifies ... lagging p.f. For capacitive loads the effect of flux is partly distorting and partly strengthening.

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 

Description : In a 3 -phase alternator, if there is only magnetizing armature reaction, the load is :  (A) capacitive (B) inductive (C) resistive (D) inductive and resistive

Answer : In a 3 -phase alternator, if there is only magnetizing armature reaction, the load is : capacitive 

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 : 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

Answer : 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

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

Answer : The armature reaction in a synchronous generator supplying leading power factor load is magnetizing and cross-magnetizing

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.

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

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

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.

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

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 : Why is the armature of DC generator laminated?

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

Description : Armature control of DC motor

Answer : Armature control of DC motor

Description : State advantages of short pitch winding over full pitch winding in alternators. 

Answer : Advantages of Short Pitch Winding over Full Pitch Winding in Alternators: 1) Short pitching reduces the amount of copper needed for end connection when compared with full pitched coil. 2) They ... reduced, thereby increasing the efficiency. 4) The power quality of generated emf is improved. 

Description : Damper winding in a synchronous motor

Answer : Damper winding in a synchronous motor Serves to start the motor.

Description : A certain transformer has 200 turns in the primary winding, 50 turns in the secondary winding and 120 volts applied to the primary. What is the voltage across the secondary?  (A) 30 Volts (B) 480 Volts (C) 120 Volts (D) 60 Volts

Answer : A certain transformer has 200 turns in the primary winding, 50 turns in the secondary winding and 120 volts applied to the primary. What is the voltage across the secondary?  (A) 30 Volts (B) 480 Volts (C) 120 Volts (D) 60 Volts

Description : A _________ is used to measure the stator % winding temperature of the generator.  (A) Thermocouple (B) Pyrometer (C) Resistance thermometer (D) Thermometer

Answer : A Resistance thermometer is used to measure the stator % winding temperature of the generator. 

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 : Damper winding is provided in 3 phase synchronous motors to :

Answer : Damper winding is provided in 3 phase synchronous motors to : provide starting torque and prevent hunting

Answer : In D.C. machines fractional pitch winding is used to reduce the sparking.

Answer : The starting winding of a single-phase motor is placed in stator.

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