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  • Henry Choi thinks this is interesting:

dangerous to open-circuit the field winding, especially in a large unloaded motor. There may be sufficient ‘residual’ magnetism left in the poles to produce significant accelerating torque to lead to a run-away situation. Usually, field and armature circuits are interlocked so that if the field is lost, the armature circuit is switched off automatically

From

Cover of Electric Motors and Drives, 4th Edition

Note

Is this talking about "freewheeling"?