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Partial Discharge (PD) Testing
Partial Discharge (PD) Testing: A Practical Q&A Guide
Electric equipment such as high-voltage transformers, motors, cables, and switchgear is subjected to high electrical stresses due to constant power flow. An unexpected breakdown of this high-voltage equipment is one of the biggest pain points in the electrical system.
In most cases, the failure does not show up as a short circuit but with a hidden insulation weakness, which grows over time if left unattended. The earliest measurable sign of this hidden damage is Partial Discharge (PD). This is why PD has become a critical predictive maintenance and condition-monitoring tool.
PD testing helps to early detection of insulation defects, reduce unplanned downtime, extend the life of equipment, and improve electrical system reliability and efficiency.
This article addresses in detail partial discharge (PD) and the most commonly asked queries on PD testing.
What is Partial Discharge?
Partial discharge is a phenomenon in which voltage breakdown or high voltage differential occurs across or through an insulator.
Fig.1. Different Types of Partial Discharges; Image Credits: ResearchGate
As shown in Figure 1, partial discharge can occur in four types:
Internal Discharges
Small gaps or defects present in the electrical element. It is often caused by low insulation quality, improper curing, trapped moisture or gas, and aging under the head.
Surface Discharges
These occur at the surface of the insulation. Common triggers causing surface discharges are dust, oil films, humidity, and weathered or damaged insulation.
Treeing
It is a small breakdown that spreads in branch-like patterns. It is caused by continuous overvoltage, impurities, and long-term electrical stress.
Corona in Air
It is a type of partial discharge formed in air around high voltage conductors, where the electric field is concentrated. High voltage levels, poor geometry, and tight clearances are the typical causes.
Partial discharge does not span the whole insulation. The location and the voltage of the partial discharge occur are dependent on the construction of the electrical system. PD activity, therefore, is an indicator of issues inside and outside the insulation.
Accurate Partial Discharge Testing in the UAE by Asset Condition Monitoring
Partial discharge activity is an early warning sign that should not be ignored. In the UAE’s demanding operating conditions, early detection of insulation issues is critical for reliable power systems. Asset Condition Monitoring provides advanced partial discharge testing and monitoring solutions across the UAE to help identify problems before they lead to unplanned outages.
Frequently Asked Questions
Partial discharge happens when high voltage creates very strong electric stress inside or around an insulator. Even though an insulation looks smooth and solid, it contains tiny air voids or defects where the stress becomes concentrated. Locally, these tiny gaps break down, producing electrical sparks without causing a full short circuit. These small discharges, called the partial discharges, slowly damage the insulation and can lead to failure.