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

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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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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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129 views 1 answer
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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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Description :

Answer :

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

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Description :

Answer :

The material for commutator brushes is generally carbon.

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Description :

Answer :

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

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Description :

Answer :

Copper brushes in D.C. machine are used where low voltage and high currents are involved.

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Description :

Answer :

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

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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

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Description :

Answer :

If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will stop.

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Description :

Answer :

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

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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 :

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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Description :

Answer :

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

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Description :

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 of an unsaturated D.C. machine is crossmagnetising.

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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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Description :

Brushes of DC machine are made up of ?

Answer :

Brushes of DC machine are made up of carbon.

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Description :

For a short transmission line with r/x ratio of is 1.0, the regulation will be zero when the load power factor is

Answer :

For a short transmission line with r/x ratio of is 1.0, the regulation will be zero when the load power factor is 0.707 lead

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147 views 1 answer
Description :

The initial rate of rise of current through a coil of inductance 10 H when suddenly connected to a D.C. supply of 200 V is_______Vs.

Answer :

The initial rate of rise of current through a coil of inductance 10 H when suddenly connected to a D.C. supply of 200 V is 20 Vs

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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 :

what is mean by short transmission line ?

Answer :

The transmission lines which have length less than 80 km is known as short transmission lines.

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Description :

A moving coil of meter has 100 turns, and a length and depth of 10mm and 20mm respectively. It is positioned in a uniform radial flux density of 200 mT. The coil carrier current capacity is 50 mA. The torque on the coil is

Answer :

A moving coil of meter has 100 turns, and a length and depth of 10mm and 20mm respectively. It is positioned in a uniform radial flux density of 200 mT. The coil carrier current capacity is 50 mA. The torque on the coil is 200µNm

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372 views 1 answer
Description :

The inductance of a coil can be increased by?

Answer :

The inductance of a coil can be increased by choosing core material having high relative permeability.

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Description :

Answer :

A moving-coil permanent-magnet instrument can be used as ammeter by using a low resistance shunt.

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98 views 1 answer
Description :

State the effects of low power factor on efficiency and voltage regulation of short transmission lines. 

Answer :

i) Effect of Low power factor on efficiency:- When power factor of load reduces current drawn by transmission line increases so copper losses in transmission line increases, hence transmission ... increases, so voltage drop in transmission line increases so regulation increases. (Become Poor) 

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113 views 1 answer
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 :

Explain the procedure to perform Short Circuit test on single phase transformer with circuit diagram.

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Description :

3X3 inverse of matrix short trick

Answer :

3X3 inverse of matrix short trick

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267 views 1 answer
Description :

Describe the difference between an open circuit and a short circuit.

Answer :

Open circuit means the wire is cut meaning power will not flow and close circuit means wire is not cut and hence power will flow.Short circuit is the same as close circuit

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7.8k views 3 answers
Description :

If the % reactance upto the fault point is 20%, then the short circuit current will be

Answer :

If the % reactance upto the fault point is 20%, then the short circuit current will be 5 times the full load current

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2.7k views 1 answer
Description :

Which of the following are known as the short circuit parameters of a 2- port network? (A) Z- parameters. (B) H- parameters. (C) Y- parameters. (D) A,B,C,D, parameters.

Answer :

Which of the following are known as the short circuit parameters of a 2- port network? (A) Z- parameters. (B) H- parameters. (C) Y- parameters. (D) A,B,C,D, parameters.

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Description :

Answer :

Reactance relay is preferred for phase fault on short transmission line.

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98 views 1 answer
Description :

Answer :

The short circuit in any winding of the transformer is the result of impulse voltage.

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150 views 1 answer
Description :

Answer :

Short circuit test on transformers is conducted to determine copper losses.

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134 views 1 answer
Description :

In which fault the maximum short circuit current occurs?

Answer :

In three phase bolted fault the maximum short circuit occurs.

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101 views 1 answer
Description :

What can cause a short circuit?

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Description :

Answer :

Primary is high voltage side and Secondary is low Voltage side.

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109 views 1 answer
Description :

Answer :

In short circuit test of transformer the low voltage side is short circuited . On high voltage side the voltmeter is connected in parallel and ammeter in series and also a wattmeter is ... circuit test is done for determining impedance and losses. In this test iron losses is neglected.

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144 views 1 answer
Description :

State the function of overload coil and No volt coil in dc motor starter.

Answer :

Function of Overload Coil: When DC motor is overloaded, the overload coil carries the overload current and produces strong magnetic field to attract a plunger, which short the terminals of ... dc motor is prevented from restarting automatically on recovery of supply without starter and protected.

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68 views 1 answer
Description :

Name the material used for :- (i) Moving coil (ii) Permanent magnet in PMMC instrument.

Answer :

(i) Material used for Moving coil: Copper, Aluminum( some times)  (ii) Permanent magnets are made of special alloys such as :  Aluminum-Nickel-Cobalt (Alnicos)  Strontium-Iron  Neodymium-Iron-Boron  Samarium-Cobalt.

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149 views 1 answer
Description :

State the material used for moving coil and former for PMMC instruments. 

Answer :

Material Used for Moving Coil and Former for PMMC Instruments:  Material used for moving coil: Copper  Material used for Former: Aluminium

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135 views 1 answer
Description :

The purpose of the restraining coil in a biased differential relay is  (A) To reduce CT saturation during fault.  (B) To increase the sensitivity of the relay.  (C) To match the transformation ratio.  (D) To limit the spill current through the relay during heavy external fault.

Answer :

d

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577 views 2 answers
Description :

Permanent magnet moving coil instruments are used for

Answer :

PMME are mostly used for measuring voltage and current.

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2.6k views 2 answers
Description :

Peterson coil is used for :  (A) shunt compensation of lines (B) grounding of system neutral (B) reduce fault currents (D) connecting interconnected systems

Answer :

Peterson coil is used for : grounding of system neutral

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517 views 1 answer
Description :

A Peterson coil is ________ A) An arc generating coil B) An arc suppressing coil C) An arc inducing coil D) None of these

Answer :

A Peterson coil is An arc suppressing coil

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67 views 1 answer
Description :

The self inductance of a coil can be measured using (A) Wien’s Bridge (B) Schering Bridge (C) Anderson’s Bridge (D) Wheatstone Bridge

Answer :

The self inductance of a coil can be measured using Anderson’s Bridge

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63 views 1 answer
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