Partial Discharge (PD) Testing for Electrical Cables and Switch Gear Panels

Partial discharge (PD) testing is a nondestructive test for assessing the health of electrical insulation systems. It involves identifying the failure of specific insulation components to resist the applied electrical field, caused by factors such as deterioration, poor design, workmanship, inadequate materials, and sludge. Over the years, this testing technique has gained widespread recognition for its effectiveness in assessing the condition of electrical assets.

What is Partial Discharge?

Partial discharge is a sign of the degradation of the insulation system. Partial discharges (PD) refer to minor electrical sparks happening within the insulation of medium and high voltage electrical assets. Each specific partial discharge occurs when there’s an electrical breakdown in an air pocket within the insulation, gradually wearing down the insulation and leading to eventual failure. Conducting Partial Discharge Testing also recognized as PD testing, is crucial for evaluating the electrical insulation’s health.

The outcomes of Partial Discharge Testing play a key role in forecasting the future performance and reliability of vital assets, including:

Electrical Cables and terminations
Power transformers and the bushings
Switchgear
Motors and generators

Types Of Partial Discharge

Partial discharge breakdown of insulation results in various effects, including rays, warmth, scent, sound, electromagnetic waves, and high-frequency electric current. It can occur in different types of insulation (air, oil, solid, GIS) and at various voltage levels (from 3kV to 769kV and beyond). The three main types of partial discharge are:
Surface Partial Discharge: The most common form, occurring across the surface of the insulation, is influenced by environmental factors humidity, temperature and pollution.
Internal Partial Discharge: These discharges happen within f defects or voids within solid insulation.
Corona Partial Discharge: Occurs in gaseous dielectrics when inhomogeneous fields are present, often involving discharges from conductors into the surrounding air.

PD Testing : Advancements in Non-Invasive Techniques

Partial discharge (PD) testing has experienced significant advancements in online non-invasive and non-destructive techniques. These cutting-edge methods provide in-depth condition assessment without disrupting the system’s operation. In this article, we will explore these techniques in detail and highlight their numerous benefits.

Online Partial Discharge (PD) Testing in Power Cables

Partial discharge occurs when insulation defects arise in power cables. Implementing online monitoring for partial discharge (PD) is an effective method to maintain the reliability of electrical power systems. This technique allows for the detection of insulation failures at joints and terminations, which, if left unaddressed, can result in extended power outages. Factors contributing to partial discharge in power cables include weak insulation areas, such as particles, voids, or cracks, as well as damage to the cables or their accessories.

By strategically placing appropriate sensors at the cable system’s terminations and joints, partial discharge can be monitored either on a temporary or continuous basis. Furthermore, utilizing advanced noise suppression techniques and algorithms for separating partial discharge sources can help accurately pinpoint hazardous discharges within the cable system.

Comprehensive PD Testing Solutions

Today, PD Testing caters to a wide range of assets, from 3KV to 700KV and beyond. Whether it’s AIS, GIS, Transformers, or Cables, all can be tried online without requiring an outage. Partial discharge occurs when a confined electric field exceeds the dielectric resist capacity of a specific part of the insulation system, resulting in a flashover. While the general insulation strategy can withstand the applied electrical area, the flashover generates high-frequency current pulses that can gradually deteriorate the insulation, leading to potential catastrophic failure.

Effective Partial Discharge (PD) Testing Methods

To detect partial discharge in MV/HV switchgear, bus ducts, cables, etc., it is preferable to perform the detection while the system is live, without disrupting the power supply. Several practical methods like cable testing rely on detecting different frequency signals, using a combination of sensors to identify different types of partial discharge:

Ultrasonic Methods: Highly effective in identifying corona partial discharge, detecting ultrasonic acoustic emissions beyond the human ear’s capability.

Transient Earth Voltages (TEV): Excel at detecting internal PD, measuring TEV signals that propagate along the metal surfaces of switchgear till ground.

UHF Detection: Excellent non-contact method for identifying electromagnetic PD signals in Gas Insulated Switch Gears and Cable Terminations

HFCT/RFCT Online Cable Testing: Utilize high-frequency current transformers (HFCT) or radio frequency current transformers (RFCT) for online cable testing, measuring PD pulses that reach an external cable ground while keeping the cable in service during testing.

Partial Discharge (PD) Testing From Technomax

At Technomax, we specialize in Online partial discharge testing, offering advanced techniques for accurate electrical inspection and monitoring services for health assessment. Our experts are adept at identifying and mitigating potential issues, ensuring the reliable and safe operation of your electrical assets. Contact us today to explore our partial discharge testing services and safeguard the health of your electrical infrastructure. Trust in Technomax for expertise and excellence in our condition monitoring services as partial discharge testing.

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