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Partial Discharge

PD Causes and Effects

Partial Discharge ImageWhat’s a Partial Discharge?
A Partial Discharge (PD) is an electrical discharge or spark that bridges a small portion of the insulation between two conducting electrodes.

PD can occur at any point in the insulation system, where the electric field strength exceeds the breakdown strength of that portion of the insulating material.

PD can occur in voids within solid insulation, across the surface of insulating material due to contaminants or irregularities, within gas bubbles in liquid insulation or around an electrode in gas (corona activity).

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PD Emissions

Partial Discharges emit energy as:

  • Electromagnetic emissions, in the form of radio waves, light and heat
  • Acoustic emissions, in the audible and ultrasonic ranges
  • Ozone and nitrous oxide gases

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How PD activity leads to failure

PD activity provides clear evidence that an asset is deteriorating in a way that is likely to lead to failure.

The process of deterioration can propagate and develop, until the insulation is unable to withstand the electrical stress, leading to flashover.

The ultimate failure of HV/MV assets is often sudden and catastrophic, producing major damage and network outages.

PD Detection & Measurement Technologies

Transient Earth Voltages(TEVs)
Measuring TEV emissions is a highly effective way of detecting, quantifying and locating PD activity in live assets.

The importance of TEV effects (discharges of radio energy associated with PD activity) is the key to our technical leadership in PD detection and measurement.

TEV sensors are employed in all of our core PD instruments. This makes them far superior to products that only measure ultrasonic emissions.

PD activity creates emissions in both the audible and ultrasonic ranges. The latter is by far the most valuable for early detection and measurement.

All of our latest handheld PD instruments employ ultrasonic sensors, in addition to TEV sensors. This combination of technologies is unique in instruments of this size and versatility.

Most importantly, the trigger points on our instruments are precisely set to indicate critical PD activity, which is immediately apparent to the user, regardless of their level of expertise. No other handheld PD instruments on the market provide information of this accuracy and value.

PD Monitoring of GIS

The PD monitoring of GIS is essential for planning the maintenance and repair of GIS equipment, especially where failure would lead to loss of production, danger to personnel or environmental risks. New European legislation on SF6 switchgear gasses means it has never been more important to monitor, maintain and manage GIS equipment.

The PD monitoring of GIS system can be retro-fitted to almost any GIS system, with specially developed PD sensors, linked by a unique ‘daisy chain’ configuration that minimises wiring, making installation easy.

The system can support over 200 separate sensors, allowing monitoring and reporting on each asset individually, to provide vital data on the condition and safety of GIS equipment. The system also includes a powerful processor with bespoke software that continually analyses the data to provide clear and meaningful reports, including fault location, severity and frequency.

This provides reassurance of safe operation under normal operating conditions, as well as identifying faults early and raising the alarm via text or email if PD activity ever reaches critical levels.