Offline Partial Discharge Diagnostics of MV Cables

Most outages in electrical power distribution systems are related to Medium Voltage (MV) cables. Aging and workmanship are two main reasons for underground cable faults. Tan Delta (TD) is the most popular diagnostic test to assess the aging and overall condition of MV cables with extruded insulation. Cables and accessories can pass Tan Delta and VLF withstanding tests and yet may show significant Partial Discharge (PD) pulses. The PD test is a complementary tool to cover some blindness of other testing methods.

PD pulses reduce the lifetime of assets by deteriorating insulation at the weak spot. The PD test is a more predictive diagnostic test in comparison with TD. The test report adds valuable information to asset management systems in order to perform condition-based maintenance. Offline PD tests can find the trigger voltage level for PD pulses, localize PD in a shielded cable, and measure apparent discharges in Picocoulomb.

Calibration is a necessary step to measure apparent discharges in Picocoulomb based on the IEC60270 standard. Understanding the concept of calibration helps us to simply comprehend the basics of PD measurement. This presentation will illustrate attenuation and dispersion effects on PD pulses and explain background noise. As PD pulses can easily be buried by environmental noise and corona discharges, we will also discuss some of the best practices to filter or minimize background noise as much as possible.

This webinar will discuss the testing setup, calibration, noise, appropriate excitation voltage, and PD report. We will talk about excitation voltage and review the advantages and disadvantages of VLF, Damped AC (DAC), and Cosign Rectangular (CR) for different field scenarios.

This is a free webinar

All webinar attendees are eligible to receive 1 NETA CTD and 1 PDH or 0.1 CEU. 

Sha Farhang is a P. Eng, an experienced electrical field engineer and master electrician in USA and Canada. He is an applications engineer at Megger with a focus on Partial Discharge testing and online monitoring. With research and lab testing, Sha is focused on developing a deep understanding of PD diagnosis and interpreting results.

Shahryar provides technical and engineering support for online and offline PD testing including medium voltage cables, transformers, and gas-insulated substations. He has previously worked with Magna IV Engineering on several commissioning and maintenance medium and high voltage projects in the USA, Canada, and Chile.