Partial Discharge Testing

What is Partial Discharge?

Partial discharges are generally a result of local electrical stress concentrations in the insulation or on the surface of the insulation and are often accompanied by the emission of sound, light, heat, or chemical reactions. Partial discharges are small electrical sparks that occur within the insulation of medium and high voltage electrical assets. These discharges erode insulation and eventually result in insulation failure.

Partial Discharge Types

Partial Discharge types include:

• Electrical floating potential
• Surface discharge
• Corona
• Void in solid insulation
• Cavity in liquid
• Electrical tree (void) around a sharp point

Monitoring & Predictive Diagnostics

Data obtained through Partial Discharge Testing and Monitoring can provide critical information on the quality of insulation and its impact on overall equipment health. Because partial discharge activity is often present well in advance of insulation failure, Asset Managers can monitor it over time and make informed strategic decisions regarding the repair or replacement of the equipment. These predictive diagnostics help companies to prioritise capital and MRO investments before an unexpected outage occurs. Partial discharge testing results can help predict future performance and reliability of critical assets, including:

• Power transformers and bushings
• Switchgear
• Motors and generators
• Cables, splices and terminations

Acceptance Testing & Quality Assurance

Failures are not limited to service aged equipment. Acceptance testing on newly-installed equipment builds-in reliability right from start-up. Acceptance testing can:

• Verify original manufacturers test data and identify damaged insulation that occurred from improper transportation/installation, poor design, and/or poor workmanship during or after installation.
• Identify premature failures and capture baseline data to trend asset health over the asset's life cycle to ensure maximum ROI.

Conclusion

The partial discharge measurement is a suitable method to detect and localize imperfections in the high voltage insulation system and provides a procedure for quality assurance of electrical equipment.