A DC motor fails to start when switched ON. What could be the possible reasons and remedies?

When power is firs applied to a motor, the armature is not rotating. Under these conditions the counter Emf is zero and only factor limiting the current in the armature is the armature resistance. The armature resistance of a motor is very small. Therefore the current through the armature would be very small. Therefore the current through the armature would be very large if power were applied to the motor. This current might produce an excessive voltage drop, affecting other equipment. Additional resistance must be connected in series with the armature to limit the current .Until the motor rotation can build up the Counter Emf. The resistance is gradually cut out as the meter rotation builds up the Counter Emf.

What will happen if a shunt motor is directly connected with load?

The flux of the shunt motor remains constant. If a shunt motor is directly connected to the supply line, the current increases. The increases the Armature current decrease the counter emf . The decreases the counter emf decrease the speed of the motor.

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