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

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Answer :

The demagnetising component of armature reaction in a D.C. generator reduces generator e.m.f.

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Description :

Answer :

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

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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.

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199 views 1 answer
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 

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84 views 1 answer
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

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253 views 1 answer
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

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56 views 1 answer
Description :

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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141 views 1 answer
Description :

Answer :

The armature core of a D.C. generator is usually made of silicon steel.

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Description :

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.

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145 views 1 answer
Description :

Answer :

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

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141 views 1 answer
Description :

Answer :

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

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134 views 1 answer
Description :

Answer :

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

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134 views 1 answer
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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83 views 1 answer
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 

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368 views 1 answer
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

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127 views 1 answer
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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227 views 1 answer
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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533 views 1 answer
Description :

Explain the nuclear chain reaction in a nuclear power plant.

Answer :

Nuclear chain reaction in a nuclear power plant: If a slow moving neutron hits unstable heavy nucleus of nuclear fuel U235 or Pu239 , the neutron is absorbed, the nucleus splits into two more ... chain reaction can be controlled and desired heat energy can be obtained in nuclear power plant. 

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Description :

The transfer of energy for reaction turbines is based on _______ A) Newton’s first law B) Newton’s second law C) Newton’s third law D) All the above

Answer :

The transfer of energy for reaction turbines is based on Newton’s third law

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Description :

The ratio of limiting friction and normal reaction is known as?

Answer :

The ratio of limiting friction and normal reaction is known as coefficient of friction.

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131 views 1 answer
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.

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454 views 1 answer
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.

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Description :

Answer :

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

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Description :

Answer :

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

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Description :

Answer :

The armature torque of the D.C. shunt motor is proportional to armature current.

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108 views 1 answer
Description :

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.

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Description :

Answer :

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

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Description :

Answer :

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

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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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194 views 1 answer
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

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Description :

Answer :

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

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97 views 1 answer
Description :

Answer :

The armature current of the synchronous motor has large values for low and high excitation.

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Description :

Why is the armature of DC generator laminated?

Answer :

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

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157 views 1 answer
Description :

Armature control of DC motor

Answer :

Armature control of DC motor

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141 views 2 answers
Description :

Answer :

In a separately excited generator supplying rated load the armature reaction is always present.

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101 views 1 answer
Description :

Armature reaction mmf and leakage reactance of a synchronous machine are determined by (a) open circuit test and short circuit test (b) open circuit test and zero power factor test (c) zero power factor test only (d) short circuit test only  

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150 views 0 answers
Description :

A d.c. shunt motor runs at no load speed of 1140 r.p.m. At full load armature reaction weakens the main flux by 5%. Whereas the armature circuit voltage drops by 10%. The full load speed of the motor is (a) 1200 r.p.m. (b) 1080 r.p.m. (c) 1040 r.p.m. (d) 1000 r.p.m.

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149 views 0 answers
Description :

The no load speed of a d.c. shunt motor is 1140 rpm. At full load, the armature reaction weakens the main flux by 5% whereas the armature circuit voltage drops by 10%. The motor full load speed in rpm will be: (A) 1080 (B) 1203 (C) 1000 (D) 1200

Answer :

The no load speed of a d.c. shunt motor is 1140 rpm. At full load, the armature reaction weakens the main flux by 5% whereas the armature circuit voltage drops by 10%. The motor full load speed in rpm will be: 1080

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241 views 1 answer
Description :

Answer :

In D.C. generators, current to the external circuit from armature is given through commutator commutator.

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142 views 1 answer
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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96 views 1 answer
Description :

Which of the following quantity maintains the same direction whether a D.C. machine runs as a generator or as a motor a. Induced e.m.f. b. Armature Current c. Field Current d. Supply Current  

Answer :

Which of the following quantity maintains the same direction whether a D.C. machine runs as a generator or as a motor a. Induced e.m.f. b. Armature Current c. Field Current d. Supply Current  

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Description :

The induced emf in the armature of a wave wound 4-pole d.c. machine having 100 armature conductors rotating at 600 r.p.m. and with a flux of 1 Wb per pole is (a) 1000 V (b) 2000 V (c) 200 V (d) 100 V

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60 views 0 answers
Description :

 The number of parallel paths in the armature winding of a 4 -pole, wave connected d.c. machine having 28 coilside is : -  a) 28 b) 14 c) 4 d) 2

Answer :

2

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450 views 2 answers
Description :

Answer :

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

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112 views 1 answer
Description :

Answer :

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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2.9k views 1 answer
Description :

Answer :

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

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Description :

Answer :

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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155 views 1 answer
Description :

Answer :

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

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