Pole drop testing on rotating machines
Mechanical stress in rotor windings cause inter turn faults (short circuits), which can lead to magnetic imbalance in generators and motors. This causes higher shaft vibrations, resulting in stress and damage to the bearings. Similar to sweep frequency response analysis (SFRA), the pole drop test is performed on single pole windings when the machine is in a standstill condition.
An AC current is injected into the slip rings to energize the pole windings. By measuring the voltage drop of every pole between the pole winding connectors, the impedance can be determined. A comparison of the measurement results of each pole or with previous measurements identifies possible inter turn faults in the pole winding.