Answer / nanchu

field failure relay will protect the system and motor
supply will become cutoff,it is preventing the series motor
action.

Answer / satyam

it gets infinite speeds by damaging the motor

Answer / satya

when field winding is removed at that instant motor tends to
go for infinite speeds , but due to the presence of stator
,it stops because the flux is zero

Answer / darababu

motor stop as there will not be no torque..and protected by relay..

Answer / amolkarne

'dc shunt motor' will decrease speed & stop

it is the 'dc series motor' which will rotate at infinately
high sppeed after opening of supply

Answer / r.manikanta

when field fails the flux produces is decreases. according
to the condition emf induced in motor is directly
proportional to speed. when field flux decreases the emf
induced is also decreases so the speed decreases.

Answer / sankarnarendra

In general case speed is inversely proportional to flex i.E n will be decrease but in case of torque is directly prop to i current will be zero i.E torque is zero

Answer / muhammad haseeb

When suddenly field circuit is open then flux will decrease .As flux decrease the speed of the motor increase firstly.Because speed and flux are inversely proportional to each other. And then speed decrease because field current is zero , flux is zero

Answer / b nandakumar

If the motor is running on load, armature draws more current torque proportional to flux ,Ia
here flux is 0 then Ia increases and is protected by starter.

Answer / andrew cottrell

Of course, the proof of the pudding is in the eating. One has to experiment & see.
But I would guess that the motor would NOT necessarily speed up. Because the motor is coupled to a driven machine which provides a resistance to speed change. I think that the danger lies in a transient over voltage due to the collapse of the flux. This could stress the insulation, and/or cause a flash over across the mica, and therefore between brushes... BUT, I don't know!! I am guessing!

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