In a differentially compounded D.C. motor, if shunt field suddenly opens the motor will first stop and then run in opposite direction as series motor.
Answer : If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses.
Answer : If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens this will make armature to take heavy current, possibly burning it.
Answer : If the field of a D.C. shunt motor gets opened while motor is running the motor will attain dangerously high speed.
Answer : The armature may burn if the back e.m.f. of a D.C. motor vanishes suddenly.
Answer : For a D.C. shunt motor if the excitation is changed torque will change but power will remain constant.