Question 128Electricity & Electronics - QMED

The correct answer is D) overspeed due to reduced CEMF. In a DC compound motor, the shunt field provides the main magnetic flux. If the shunt field is weakened by excessive rheostat resistance or an open circuit, the motor's back EMF (CEMF) will be reduced. This allows the armature to spin faster, resulting in an overspeed condition. The reduced CEMF is unable to counter the applied voltage, leading to the motor overspeeding. The other options are incorrect because: A) the motor would not continue to run at base speed with a weakened shunt field, B) the motor would not stop due to low flux, and C) the motor would overspeed rather than slow down and overheat.