# Frequent question: What will happen when the field of a DC shunt motor gets opened while the motor is running?

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If the shunt field suddenly opens while the motor is being operated under full-load conditions, only a small voltage due to the residual magnetism of the pole pieces will be induced into the armature. Current will increase considerably. … Under these conditions, the motor will act as a series DC motor.

## What will happen when the field of a DC shunt motor gets opened while the motor is running Mcq?

4. What will be the effect of opening of field of a DC shunt motor while motor is running? Explanation: In a DC shunt motor if supply for the field winding is cut down, the speed would dangerously increase in order to maintain the back emf of the motor.

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## What will happen if the field of the DC motor is opened accidentally in no load and full load?

The field will be reduced to only to the value of residual flux. The speed will be very high. The parts of motor may even fly apart.

## What will happen if the shunt field winding of a loaded shunt motor accidentally breaks?

Ans: if the shunt field winding of a loaded shunt motor accidentally breaks, the loss of shunt field current would result in stopping of the motor or burn out the armature or fuse.

## What will happen if shunt field suddenly opens in a differential compound DC motor?

Explanation: If shunt field is suddenly opened, flux due to shunt field will become 0. As, net flux is equal to shunt field flux – series field flux, the direction of flux will be reversed and thus motor will run in opposite directions.

## What will happen if DC shunt motor is connected across AC supply?

1. What will happen if DC shunt motor is connected across AC supply? Explanation: In case of parallel field connection, it won’t rotate at all and will start humming and will create vibrations, as a torque produced by positive and negative cycle will cancel out each other. DC motor will be heated up and it may burn.

## What is the effect in a DC shunt motor if its supply terminals are interchanged?

When both (the direction of the field as well as that of armature current) are reversed the direction of rotation will not change. So in the case of DC shunt motor, if the supply terminals are interchanged, there is no change in the direction of rotation.

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## What will happen if the field circuit breaks down?

Motor runs at dangerously higher speeds before its armature get melt due to higher currents. Originally Answered: What would happen if a field circuit opened during the starting up of a DC motor? The DC Motor does not run then there is no back EMF. Therefore there is no opposing force for input armature current.

## What is the effect of inserting resistance in the field circuit of a DC shunt motor on its speed and torque?

In this method, speed variation is accomplished by means of a variable resistance inserted in series with the shunt field. An increase in controlling resistances reduces the field current with a reduction in flux and an increase in speed.

## What will happen if shunt field resistance is too large?

Answer: n d.c shunt motor if field winding supply is removed the motor back emf will drop to zero, hence the armature will draw more current to make up the emf. this results in blowing up of fuse.

## What would happen to the DC shunt motor if it is started with full load attached?

On adding a load to the shaft, the motor does slow down initially, but this is where the concept of self regulation comes into the picture. At the very onset of load introduction to a shunt wound DC motor, the speed definitely reduces, and along with speed also reduces the back emf, Eb.

## What happen when load to the DC motor is suddenly increased?

The speed will suddenly increase to a dangerously high level, or it will reach a speed where the friction and windage losses provide sufficient load to limit speed, ie most power tools.

## What will happen if the back EMF of a DC motor vanishes suddenly?

Detailed Solution. If back emf of a dc motor vanishes suddenly, motor circuit will try to retain back emf by drawing more current from supply. As the back emf vanishes zero, the whole supply voltage appears across armature and heavy current flows.

## Why is the speed of DC shunt motor dependent on back EMF?

In the case of DC motors Speed ∝ Back emf(Eb)/flux(φ). The field winding is connected across the armature. The resistance offered by the field is constant so the current is constant. … Therefore the speed of the DC shunt motor depends on the back EMF.

## Which speed can be obtained from field control of DC shunt motor?

6. Which speeds can be obtained from field control of DC shunt motor? Explanation: Speeds greater than rated speeds can be obtained by lowering the flux of shunt field motor.