DC Motors
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

Armature is temporarily open circuited
A high value resistor is connected across the field winding
A resistance is connected parallel to the armature
A resistance is connected in series with armature

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DC Motors
If a D.C. motor designed for 40°C ambient temperature is to be used for 50°C ambient temperature, then the motor

Of higher H.P. should be selected
Of lower H.P. should be selected
Is to be de-rated by a factor recommended by manufacturer and select the next higher H.P. motor
Can be used for 50°C ambient temperature also

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DC Motors
If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens

Nothing will happen to the motor
Motor will run at very slow speed
This will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses
This will make armature to take heavy current, possibly burning it

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DC Motors
In a dc compound machine,

Both play equally dominant role
Series field winding plays dominant role
Shunt field winding plays dominant role
Either can play dominant role

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