What is Partial Discharge Measurement (PD Measurement)?
Partial Discharge Measurement (PD Measurement) is an alternative to high-voltage testing & is used in routine & type testing of many electrical equipment.
It is one of the most effective non-destructive ways for discovering insulation faults in the electrical equipment.
PD measurement is thus utilized for quality testing in the manufacturing as well as on-site testing of cables, GIS, power transformers, instrument transformers, rotating equipment, and their components.
Depending on the DUT, HIGHVOLT develops application-specific PD devices/systems.
Partial discharge (PD) activity is frequently detected well before insulation failure; partial discharge monitoring is the most visible indicator of faults & degradation in
- Transformers,
- Turbines,
- Motors,
- Cable, and
- Switchgear.
Partial discharge happens inside insulation in equipment including
- Transformers,
- Turbine generators,
- Motors,
- Switchgear, and
- Cables.
Partial discharge happens when one component of the insulation cannot tolerate the electric tension that is applied to it and flashes over.
At that point, the gases are ionized, the voltage rapidly declines, and the current pulse must balance the residual charge in the remaining insulation.
It is a rapid process that can shorten the asset’s life.
Partial discharge happens in electrical assets with insulation, such as
- Transformer bushings,
- Switchgear,
- Cables,
- Turbine generators,
- Motors, and more.
This can happen at any voltage level.
Methods for measuring Partial Discharge
1). Electric (Conventional)Method
Electrical PD measurement (IEC 60270) measures the apparent charge in pC, that is the integrated current pulse generated by a PD that runs through the test circuit.
The standard method provides for exact calibration, but the measuring circuit must have a sufficiently high signal-to-noise ratio (SNR) to easily resolve the PD signal in question.
2). UHF (Ultra High Frequency Method
UHF (ultra-high frequency) The electromagnetic emission of a PD source is measured with a UHF antenna put into the transformer tank via an oil-sampling valve.
The tank’s metal surface works as a natural Faraday cage, filtering away electrical interference from the outside. UHF readings may not be calibrated using IEEE (or) IEC standards for factory PD acceptance testing of transformers.
3). Ultrasonic (Acoustic) Method
The primary objective of permanently placed online acoustic monitoring systems is to send an early warning of an impending issue to a remote site, which may then be followed by additional field tests.
These measures are typically performed in reaction to aberrant gas-in-oil test findings or sounds that could suggest partial discharges.
Causes for Partial Discharge
PD can result from a wide range of causes. Many are the result of human mistake, such as contamination, improper installation, or manufacture faults.
Some of the factors are environmental, such as temperature and humidity. PD can also arise as the insulation ages.
Windings account for 26% of transformer failures.