What is it used for?

Measurement of Partial Discharge (PD) in motors and generators is used to assess the condition of insulation systems, typically together with other test methods. PD results can provide an early warning of insulation breakdown before a surge test or hipot test fails. It is a great tool to track the condition of equipment over time and can provide an opportunity to lengthen the remaining life of a motor.

For a rotating piece of equipment in use, partial discharge during operation or during a test is not necessarily bad, but it can be. There is not a level of partial discharge measurement that is defined as good or bad in the standards. However, rising PD over time, and/or a lower PD Inception Voltage (PDIV) over time typically indicates breakdown or weakening of the insulation.

Along with a set of other winding tests, and for users of motors – observations of the behavior of the motor during operation, PD measurements can be used as a tool to confirm suspicions that a motor has problems. In a motor shop or in the field it can be a tiebreaker in the determination of pass/fail and can determine whether to schedule reconditioning /replacement or not.

Partial Discharge tests can also be used to find problems in systems powered by inverter drives (VFD or ASD). For more information click the link at the bottom of this page.

In coil and rotating equipment manufacturing, partial discharge measurements are used for quality control to confirm that there is no PD or that the PD is below a certain level.

How Partial Discharge measurement works

There are numerous technologies used to detect and measure Partial Discharge. First a voltage is applied to the device under test (DUT) from an AC voltage source, AC Hipot tester or Surge tester. A detector such as an audio receiver, RF receiver or a capacitive coupler connected to electronic signal processing devices pick up the partial discharges and quantifies the magnitude.

Electrom Instruments does the partial discharge measurement during a surge test. A capacitive coupler picks up the PD spikes and feeds them to an oscilloscope and computer for processing. Partial Discharge levels in mV and the RPDIV and RPDEV, according to IEC 61934, are displayed and recorded. The test results are automatically stored and can be compared to earlier results if the test is part of a maintenance or reliability program.

Combining the surge test with a partial discharge measurement is a fast and cost effective way to get partial discharge measurements. No accessories, couplers or other gadgets are required. All the required pieces are included inside the iTIG II motor tester and winding analyzer.