# Why is it dangerous to lose the field of a shunt motor?

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## What will happen if the field of the DC shunt motor is accidentally removed?

If field winding is disconnected accidentally, the speed would dangerously increase in order to maintain the back emf of the motor. For a constant back emf, flux is inversely proportional to the speed of the motor.

## Why should the field of a DC shunt motor not be opened?

The shunt field must never be opened while the motor is running. 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.

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## What happens if the field winding of a running shunt motor suddenly breaks open?

As we know, if the field winding of a running shunt motor suddenly breaks open. So, Flux is reduced and speed increase dangerously as flux is inversely proportional to speed.

## What will happen if a shunt motor running at no load has its shunt field winding opened accidentally?

What will happen if the d.c. shunt motor opened accidentally running on no-load has its shunt field winding? 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 is the danger of an open field circuit on a series motor?

As mentioned above if the field circuit is opened, the back emf will drop to zero. With full armature voltage applied this will cause a very large armature current to flow which should normally blow the fuses. While the field current decays the motor will speed up as if in a field weakening mode.

## What would happen if the field of DC shunt motor is opened 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.

## What is the function of the field loss relay?

Field Failure Relay, also known as Field Loss Relay protects the D.C. Shunt wound motor or main circuit, under open field conditions, or in the absence of the field supply. Speed of the Shunt Wound D.C. Motor increases as the field supply is weakened.

## What will happen if a resistance is connected in series with the field of a shunt generator?

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. This method of speed control is independent of load on the motor.

## What will happen if the back emf of dc motor vanishes?

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.

## What would happen if the load was lost while running a series connected DC motor?

From the emf equation we know speed varies inversely with the flux and in series motor flux varies directly with armature current . So at no load the flux is less and speed is enormoualy high and could mechanically damage the machine . A series wound DC motor will run away if the load is removed.

## What happens if field winding of the synchronous motor is short circuited?

Now the rotor winding of the synchronous motor is analogous to that of an induction motor. Therefore if we short circuit the field winding of a synchronous motor then it will behave as an induction motor.

## 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.

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