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If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor is to be derated by a factor recommended by manufacturer and select the next higher H.P. motor.

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Description :

State the insulating materials used in motor. Write temperature class and withstand temperature ranges for them. 

Answer :

The insulating materials used in motor are as belows: 1. Cotton, 2. Silk, or paper, 3. Press board, 4. Resins 5. PVC 6. Cellulose-Fiber, 7. Enameled coating, etc  ... Over 180° Mica, porcelain, ceramics, glass quartz, asbestos, treated glass fiber or treated asbestos. etc.

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72 views 1 answer
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Answer :

In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to 25% of the previous value.

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164 views 1 answer
Description :

Answer :

Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have to be cumulatively compounded.

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305 views 1 answer
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Answer :

For a D.C. shunt motor if the excitation is changed torque will change but power will remain constant.

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138 views 1 answer
Description :

Answer :

The type of D.C. motor used for shears and punches is cumulative compound D.C. motor.

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114 views 1 answer
Description :

Answer :

In case the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be less than 50%.

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119 views 1 answer
Description :

Answer :

Cumulatively compounded D.C. motor will be suitable along with flywheel for intermittent light and heavy loads.

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117 views 1 answer
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Answer :

In a differentially compounded D.C. motor, if shunt field suddenly opens the motor will first stop and then run in opposite direction as series motor.

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73 views 1 answer
Description :

Answer :

If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses.

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107 views 1 answer
Description :

Answer :

The armature may burn if the back e.m.f. of a D.C. motor vanishes suddenly.

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401 views 1 answer
Description :

Answer :

If a D.C. motor is connected across the A.C. supply it will burn due to heat produced in the field winding by eddy currents.

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79 views 1 answer
Description :

Answer :

If the field of a D.C. shunt motor gets opened while motor is running the motor will attain dangerously high speed.

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108 views 1 answer
Description :

Answer :

If a D.C. series motor is operated on A.C. supply, it will spark excessively, have poor efficiency, have poor power factor.

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73 views 1 answer
Description :

The speed of a D.C. motor can be controlled by varying  1. Its flux per pole 2. Resistance of armature circuit 3. Applied voltage 4. All of the above

Answer :

The speed of a D.C. motor can be controlled by varying  1. Its flux per pole 2. Resistance of armature circuit 3. Applied voltage 4. All of the above

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148 views 1 answer
Description :

Answer :

The speed of a D.C. shunt motor can be increased by increasing the resistance in field circuit.

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98 views 1 answer
Description :

Answer :

By looking at Commutator part of the motor, it can be easily confirmed that a particular motor is D.C. motor.

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96 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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221 views 1 answer
Description :

Answer :

The speed of a D.C. shunt motor more than its full-load speed can be obtained by decreasing the field current.

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101 views 1 answer
Description :

Answer :

The direction of rotation of a D.C. series motor can be changed by interchanging field terminals.

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79 views 1 answer
Description :

Answer :

For starting a D.C. motor a starter is required because it limits the starting current to a safe value.

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66 views 1 answer
Description :

Answer :

D.C. Series motor is generally preferred for cranes and hoists.

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88 views 1 answer
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Description :

Answer :

Cumulative compound D.C. motor is preferred for elevators.

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88 views 1 answer
Description :

As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit?

Answer :

As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit a resistance is connected in series with armature.

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133 views 1 answer
Description :

Answer :

A.C. series motor as compared to D.C. series motor has smaller brush width, less number of field turns, more number of armature turns, less air gap.

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Description :

Answer :

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

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104 views 1 answer
Description :

Answer :

The current drawn by the armature of D.C. motor is directly proportional to the torque required.

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360 views 1 answer
Description :

In a 2 kW, 200 V, 1000 rpm. DC series motor the torque at full load was found to be 0.3 N -m. The torque at half full load in N -m is :

Answer :

In a 2 kW, 200 V, 1000 rpm. DC series motor the torque at full load was found to be 0.3 N -m. The torque at half full load in N -m is : 0.075

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83 views 1 answer
Description :

Answer :

At the instant of starting when a D.C. motor is put on supply, it behaves like a low resistance circuit.

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Description :

Answer :

In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will remain unchanged.

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159 views 1 answer
Description :

Answer :

Sparking, is discouraged in a D.C. motor because commutator gets damaged.

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118 views 1 answer
Description :

Answer :

Sparking at the commutator of a D.C. motor may result in damage to commutator segments, damage to commutator insulation, increased power consumption.

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141 views 1 answer
Description :

Answer :

The speed of a D.C. series motor is inversely proportional to the armature current.

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76 views 1 answer
Description :

Answer :

The starting resistance of a D.C. motor is generally low.

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89 views 1 answer
Description :

Answer :

In a D.C. shunt motor, speed is independent of armature current.

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Description :

Answer :

A D.C. series motor is that which has its field winding consisting of thick wire and less turns.

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58 views 1 answer
Description :

Answer :

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

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Description :

Answer :

As the load is increased the speed of D.C. shunt motor will reduce slightly.

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Description :

Answer :

Differentially compounded D.C. motor has got maximum self loading property.

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Description :

Answer :

Shunt motors,  Series motors, Compound motors

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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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3.0k views 1 answer
Description :

Describe the reason of using dc series motor for electric trains.

Answer :

Electric trains require an inverse torque speed characteristics for proper operation. That is a higher torque is required at start (when speed is nil or low) and as the train picks up ... torque - speed characteristics of DC series motors match, these motors are suitable for electric trains

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120 views 1 answer
Description :

Answer :

When a D.C. series motor is connected to A.C. supply, the power factor will be low because of high inductance of field and armature circuits.

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105 views 1 answer
Description :

The function of a brush and commutator arrangement in a dc motor is to  (1) produce unidirectional torque (2) produce unidirectional current in the armature (3) help in changing the direction of rotation of the armature (4) reduce sparking

Answer :

The function of a brush and commutator arrangement in a dc motor is to produce unidirectional torque

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1.7k views 1 answer
Description :

Answer :

If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens this will make armature to take heavy current, possibly burning it.

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113 views 1 answer
Description :

Answer :

If the speed of a D.C. shunt motor is increased, the back e.m.f. of the motor will increase.

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122 views 1 answer
Description :

D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select the?

Answer :

D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select the compound motor.

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85 views 1 answer
Description :

D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the?

Answer :

D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the series motor.

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213 views 1 answer
Description :

Answer :

If a D.C. motor is to be selected for conveyors, Series motor would be preferred.

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91 views 1 answer
Description :

A d.c. motor can be looked upon as d.c. generator with the power flow?

Answer :

A d.c. motor can be looked upon as d.c. generator with the power flow reversed.

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