What does a voltage regulator sense when it decreases current to the exciter field windings?

When a voltage regulator decreases current to the exciter field windings, it is responding to an increase in the voltage level. The primary function of a voltage regulator is to maintain a stable output voltage despite variations in the load or input conditions. If the voltage level rises above a certain threshold, the regulator senses this increase and reacts by reducing the current supplied to the exciter field windings. This reduction in current leads to a decrease in the magnetic field strength of the alternator, which in turn helps bring the voltage back down to the desired operating level. Therefore, the correct answer highlights the regulator's role in managing system voltage effectively by adjusting the current to maintain optimal performance.