Partial Discharge Testing

The IEC 60270 standard describes partial discharges as “localized electrical discharge that only partially bridges the insulation between conductors, and which can or cannot occur adjacent to a conductor”. The use of high voltages with thin layers of insulation makes these partial discharges increasingly likely in a high voltage system and over time they can lead to electrical failure. The likelihood of partial discharge can be increased when we operate insulation systems at high temperatures or at low pressures.

Partial discharge is usually characterised by the partial discharge inception voltage (PDIV - the voltage at which we first see partial discharge), the partial discharge extinction voltage (PDEV - the voltage at which it stops) and the number and size of partial discharges that take place at a voltage above PDIV.

The inception voltage and the nature of the partial discharge activity at voltages above this level are significantly influenced by the nature of the voltage – DC, AC sinusoidal or PWM. As such, it’s important to have the capability to test partial discharge with these different voltage types and in a range of environments – at aHV we have developed leading capability in this area.

This capability includes the ability to automate our partial discharge tests to minimise the time taken in test and maximise the quality of the data.


Relevant Standards

Partial discharge testing is supported by a range of international standards that describe procedures, testing parameters, and detection methods for different types of samples and applications.

The three key standards in respect of measurement are:
• IEC 60270 - High-voltage test techniques — Partial discharge measurements / ASTM D1868-24: Standard Test Method for Detection and Measurement of Partial Discharge (Corona) Pulses in Evaluation of Insulation Systems: These standards define methods for partial discharge testing with AC waveforms and are typically valid for frequencies of up to 2000Hz. They also provide guidance for DC partial discharge testing.

• IEC 61934 - Electrical insulating materials and systems - Electrical measurement of partial discharges (PD) under short rise time and repetitive voltage impulses: This technical specification provides details of how partial discharge can be measured in systems typically using power electronics that switch at high frequencies.

Typical Test Service

Depending on whether you are looking to test a material, a component or a system, aHV will work with you to develop a test plan that maximises the opportunity to generate the best information about the performance of your insulation system.

Step 1 – Conditioning Of Insulation: Before testing is carried out, insulation is usually conditioned in a standard environment based on the procedures stated in the ASTM D618-21 / IEC 60212 standards. Samples typically spend 48 hours in a 50% relative humidity environment at room temperature – this is a particularly important step when dealing with insulation materials that are hygroscopic and whose permittivity can vary as a function of time (which then influences the PDIV of the insulation system)

Step 2 – Setting The Correct Environment: With the sample connected we then set the appropriate environmental conditions for the test. At aHV we can deliver tests at pressures equivalent to altitudes up to 100,000ft and at temperatures from -50oC to 200oC. The time taken for this step depends on the test object. Simple samples (like dielectric films) can be tested almost instantly. Larger components like electrical machines may need extended periods of time at the operating condition.

Step 3 – Testing: Once the samples are connected, the voltage is applied. We have apply a wide range of voltage types that include:
• AC voltages – 50Hz to 2000Hz at 30kV
• DC voltages up to 30kZ
• PWM Voltages – up to 100kHz at 24kVpk-pk (depending on the test object capacitance)
The majority of our tests are carried out using automated processes that ensure the voltage is applied repeatably with low levels of harmonics (in the case of an AC test).

Contact Us

To discuss your requirements for partial discharge testing compatibility assessment, please speak to Salvador Trujillo, our Project Engineer & Test Engineer. 
Created with