DC Motors
The commutating winding is basically used in a dc machine

None of the listed here
To improve commutation
To reduce armature reaction
To control the speed of machine

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DC Motors
If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens

Motor will come to stop
This will make armature to take heavy current, possibly burning it
Nothing will happen to motor
This will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses

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