Partial Discharge (PD) Scanning

• Partial Discharge scanning is a preventative maintenance technique used to detect insulation breakdown or electrical discharge activity inside high-voltage equipment before a major failure occurs. It helps identify hidden faults in transformers, switchgear and cables —reducing the risk of unplanned outages.

PD scanning is commonly used on:

• Transformers

• Medium and High Voltage switchgear

• MV/LV cable terminations and joints

• Busbars and outdoor substations

• Rotating machines and generators
  Any high-voltage asset where insulation reliability is critical can benefit from PD assessment.

PD scanning involves:

• Using ultrasonic, UHF or TEV sensors to pick up discharge signals

• Non-invasive inspection—usually while equipment is still energised

• Data analysis to determine PD severity, type, and location

• Reporting findings with recommendations for corrective action

Common indicators include:

• Crackling or hissing sound detected during ultrasonic scanning

• Localized heating or corona activity

• Electrical noise or spikes in PD monitoring readings

• Insulation stress marks or carbon tracking
  If left untreated, these can escalate into arc faults or catastrophic equipment failure.

For critical high-voltage infrastructure, annual PD scanning is recommended, with more frequent checks (every 6 months) for aged, heavily loaded, or high-risk equipment.