Partial Discharge (PD)

Partial Discharge (PD) Knowledge Base

What is Partial Discharge (PD)? What can PD do to your HV network? Can we detect and monitor Partial Discharge on-line to help manage the condition of your HV assets?

Curious about the above questions? You are at the right place!

What is Partial Discharge (PD)?

Partial Discharge, or PD, is essentially a spark that occurs in defects in High Voltage electrical insulation. It’s called a partial discharge because the discharge only partially bridges the gap between the conductors.

The discharge may be in a gas-filled void in a solid insulating material, in a bubble in a liquid insulator or around an electrode in gas. In high voltage cable systems, PD is commonly found in joints and accessories, where a defect or void exists.

Partial discharge is generally accepted as the predominant cause of long-term degradation and eventual failure of electrical insulation.

How to Detect Partial Discharge (PD)?

When a Partial Discharge occurs, it radiates energy in different forms.

Electromatic energy can be detected directly with a UHF PD sensor, as commonly used on GIS. On Air-insulated switchgear, the electromagnetic energy induces voltage pulses on the earthed external panels, called TEVs. These can be detected using Capacitively coupled sensors. In cables and joint, the PD induces a small current pulse that propagates along the cable and can be detected using a High Frequency current transformer, or HFCT. PD also produces acoustic energy, which is detected by ultrasonic sensors. These are used for overhead lines, bushings, or cable terminations, where tracking or corona discharge occurs on the outer insulating surfaces.

Generally, PD testing is conducted on electrical assets 5kV and above.

On-line Partial Discharge (PD) Testing & Monitoring Equipment

Both portable spot testing instruments and permanent monitoring systems can be used to detect PD.

On-line PD Spot test tools are used for regular surveying of partial discharge. They range from simple handheld devices, with an in-built display showing PD activity levels, to advanced systems that record and save PD data.

On-line PD monitoring systems vary in complexity and design, depending on the environment in which they will be permanently installed. Large systems are installed in MV substations, monitoring every cable and every switchgear. More industrialised devices are used in distributed applications, such as small substations and EHV assets. PD Monitoring systems can automatically acquire, process and display data to users remotely.

Condition Based Asset Management – The PWR Cycle™

When implementing Condition Based Maintenance, or CBM, tools into your power network, it is essential to have a clear asset management plan.

The PWR Cycle™ is a framework designed to help organise, manage and implement CBM technologies. Make managing your HV assets simple and effective. It is designed to combine a variety of solutions that complement each other. Form a complete framework to maximise the performance of your network, for now, and for the future.


What’s more?

Click the links below for more Partial Discharge resources!

PD Theory

Partial Discharge theory, effects, and consequences with technical paper to support

PD Videos

Some videos of our experienced PD engineer talk you through different topics of on-line Partial Discharge


Have some questions about Partial Discharge? You can find some common PD questions and our answers to them here.


Contact IPEC

If you have any PD questions, please let us know!