Surge testing is accomplished by impressing pulses of very rapid rise from
a surge comparison tester (capacitor) into the machine windings. These
pulses each produce a damped oscillation of current, or resonant frequency,
between the capacitor of the tester and the winding. The pulse and the resulting
oscillation is monitored by means of an oscilloscope. Then by observing
the pattern on the oscilloscope, the existence and nature of the fault in the
machine winding can be determined.