What happens if the shunt field circuit of a DC compound motor suddenly breaks open?

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 happens in a shunt de motor if its field circuit opens while it 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. The magnitude of this current may be sufficient to burn out the motor.

What is the effect in a DC shunt motor if its supply terminals are interchanged runs in slow speed runs in high speed runs in the same direction runs in the reverse direction?

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

What happens to a shunt motor when the armature current decreases during operation?

So now as low current will flow through the field winding as well as armature winding ( as it is series motor) so main flux produced will be lesser, as before saturation point current is directly proportional to flux. So as main flux is lower, speed will tend to increase.

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

In the case of an induction motor, the field winding is permanently short-circuited by end rings. In a Synchronous motor, the rotor winding is supplied with DC excitation. 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.

What is a short shunt?

In a Short Shunt Compound Wound Generator, the shunt field winding is connected in parallel with the armature winding only. In this type of DC generator, the field is produced by the shunt as well as series winding. The shunt field is stronger than the series field.

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.

What is the effect on speed if part of the field winding is shorted?

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.

Does the speed of a shunt motor increase or decrease when the armature current increases?

The change in armature current and torque on supplying load is graphically shown below. This increase in the amount of torque increases the speed and thus compensating for the speed loss on loading. Thus the final speed characteristic of a DC shunt motor, looks like.

Why does the current through a motor decrease when the motor speeds up?

As the motor picks up speed, relative speed between field and rotor decreases. Therefore rotor emf decreases and hence currents in rotor and stator also decrease.