Why are field loss detectors necessary in the dc motors?

Question

Why are field loss detectors necessary in the dc motors?

Answer 1

If you lose the field the motor will run away!

Look up and study a series wound DC motor to obtain a better understanding of this. With a series wound motor if load is removed the speed will increase. The increase in speed results in a reduction of armature and field current. The reduction in field current causes the motor to continue to accelerate, further reducing field current... and so on.. until the motor is destroyed.

If you lose the field you have reduced its current to zero and the motor will begin to speed up.