In a DC shunt motor if field current is decreased then the speed of the motor is

In a DC shunt motor if field current is decreased then the speed of the motor is

Right Answer is:

Increase

SOLUTION

  • This is known as field weakening or constant power mode of operation.
  • When the field winding current reduced the Field’s magnetic strength reduced which in turn reduced the back EMF and at the same time the rotor current increases
  • Due to reduced magnetic field pole intensity rotor starts rotating faster till it develops same Back EMF which should be equal to its original value.
  • So in simple words when shunt field current If decreases, φ decreases, and the speed rises as speed is inversely proportional to flux.
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