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

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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

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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 :

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

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Answer :

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

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

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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 :

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

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Answer :

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

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

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Answer :

In a D.C. generator in case the resistance of the field winding is increased, then output voltage will decrease.

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Answer :

In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be 8.

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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 :

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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Answer :

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

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Answer :

Copper losses,iron losses,variable losses , constant losees

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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 :

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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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 :

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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Answer :

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

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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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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 :

Brushes of DC machine are made up of ?

Answer :

Brushes of DC machine are made up of carbon.

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Answer :

In D.C. generators, the brushes on commutator remain in contact with conductors which lie under interpolar region.

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

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Description :

Answer :

Lap winding is composed of any even number of conductors.

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

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The 'Equal area criterion' for the determination of transient stability of a synchronous machine connected to an infinite bus  (1) ignores line as well as synchronous machine resistance and shunt capacitances.  (2) assumes accelerating power acting on the rotor as constant.  (3) ignores the effect of voltage ... inherent damping present in the machine.  (4) takes into consideration the possibility of machine losing synchronism after it has survived during the first swing.

Answer :

1

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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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In case of conductively compensated D.C. series motors, the compensating winding is provided in series with armature winding.

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

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yes High Voltage side of Transformer winding have more number of turns. and low voltage side of Transformer winding have less number of turns.

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Description :

State the function of following parts of DC motor : i) Yoke ii) Poles iii) Field winding iv) Commutator. 

Answer :

Function : i) Yoke: The yoke serves the following two purposes. i) It supports the other components such as poles and provides mechanical protection for whole machine. ii) It forms a part of ... one pole to another and thus to help the motor to develop a continuous and unidirectional torque  

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Description :

Answer :

The insulating material used between the commutator segments is normally mica.

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Answer :

In A.C. series motor compensating winding is employed to reduce sparking at the brushes.

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Description :

Answer :

In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when number of poles is 2.

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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 :

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

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Description :

Answer :

The purpose of stator winding in the compensated repulsion motor is to improve power factor and provide better speed regulation.

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Description :

Answer :

In a capacitor start and run motors the function of the running capacitor in series with the auxiliary winding is to improve power factor.

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Description :

The damping winding in synchronous motor is generally used to?

Answer :

The damping winding in synchronous motor is generally used to provide starting torque and prevent hunting.

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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. 

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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.

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Description :

Answer :

A centrifugal switch is used to disconnect starting winding when motor has picked up about 50 to 70 per cent of rated speed.

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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. 

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Description :

Damper winding in a synchronous motor

Answer :

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

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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

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