Partial Discharge Testing- Need, Testing, and Addressing Defects

1. Partial Discharge Testing: Need, Testing, and Addressing Defects Did you know that more than 85% of disruptive failures in MV (medium voltage) and HV (high-voltage) equipment are related to partial discharge (PD)? This is why partial discharge testingis crucial for early detection and to keep your electrical infrastructure in good condition. Studies have proven that PD activity can deteriorate assets, resulting in insulation being unable to withstand electrical stress. Over time, it can lead to flash-over and equipment failure. Testing is conducted to analyze the health of electrical insulation. One of the effects of flash-over is the high-frequency current pulse traveling through the insulation’s capacitance (C1 and C3). The short, microsecond duration makes it a low- energy pulse, but it negatively impacts insulation and eventually results in catastrophic failure. Partial discharge breakdown also produces heat, light, sound, smell, HF electric current, and electromagnetic waves. Understanding partial discharge PD occurs when an aspect of an insulation system fails to withstand an electrical field it comes in contact. It is typically the result of poor workmanship or design, aging, contamination, or defective materials. Of all the available methods, partial discharge testing is the widely recognized practice for analyzing the health of electrical assets. How is it done? Online non-destructive and non-invasive techniques for surveying and monitoring are proven to deliver sufficient details for condition assessment without interrupting system operations. Modern techniques make it easier to test a wide range of assets from 3KV to 700KV and greater. Partial discharge testing can identify all types of PD: Surface PD – The most common phenomenon that occurs across the surface of the insulation. It is affected by humidity and salt air.

2. Internal PD – This occurs in voids, cavities, or defects within solid insulation. Corona PD – Occurs in gaseous dielectrics with inhomogeneous fields, usually from the conductor, directly into the air, and in outdoor electrical assets. Professionals can test air-insulated assets, GIS switchgear and busses, extruded cables, and paper-insulated cables online without causing an outage. They use various techniques, such as ultrasonic technology, HFCT/RFCT online cable testing, and transient earth voltage (TEV) methods. Some companies can perform partial discharge testing using UHF for non-contact detection with electromagnetic PD signals in cable systems, open terminal switchyards, and distribution networks.