Insight to Enhancing the Performance of the Pole Drop Test for Detecting Field Winding Turn Faults in Salient Pole Synchronous Motors

The pole drop test is the most widely applied off-line test for detecting shorted turns in the field winding of salient pole synchronous motors. It is a simple test where the voltage drop (or inductance) of the poles are compared to detect the presence of shorted turns. Although it does not require special test equipment, false indications due to sensitivity problems are common. In this letter, the voltage and inductance distribution between the poles are analyzed under shorted field turn conditions. Some practical insight for enhancing the sensitivity and reliability of the pole drop test are given based on the qualitative analysis and experimental testing on a 30 kVA synchronous motor with shorted field turns. It is shown that the sensitivity of the test is significantly higher when the test is performed with the rotor inserted, which is not reported elsewhere. It is also shown that the reliability of the test can be improved by observing the voltage or inductance in poles adjacent to the pole suspected with shorted turns.