Partial Discharge

What is Partial Discharge (PD)?

  • Partial Discharge is a localized electrical discharge that occurs within the insulation system of high-voltage equipment.
  • It does not completely bridge the insulation between two conductors but gradually damages the insulation, leading to breakdown over time.
  • PD activity is an early warning symptom of insulation deterioration. Detecting PD at an early stage prevents major failures in transformers, switchgears, cables, and rotating machines.

How PD Testing is useful?

  • Insulation deterioration is the primary cause of failure in high-voltage equipment.
  • Partial Discharge testing helps in identifying weak insulation points before they develop into catastrophic breakdown.
  • It provides condition-based monitoring, avoiding unnecessary shutdowns.
  • Helps in extending life expectancy of equipment and reducing unplanned downtime.

Applications of PD Testing

In Power Transformers
  • Detects winding insulation weaknesses.
  • Identifies voids, cracks, and surface discharges in solid insulation.
  • Prevents costly transformer outages by early detection.
In Switchgears
  • Detects defects in busbar insulation, joints, and contact systems.
  • Identifies surface tracking and corona discharges.
  • Helps in preventing switchgear flashovers and arc faults.
In Power Cables
  • Locates weak spots, joints, and terminations.
  • Identifies void discharges in cable insulation.
  • Prevents failures in underground transmission and distribution networks.

Typical Scope of Study

  • Verification of compliance with relevant standards (IEEE).
  • Continuous monitoring of PD signals during normal operating conditions.
  • Phase-resolved PD (PRPD) analysis to classify defect types.
  • Localization of PD activity using multiple sensors.
  • Trending and risk assessment for prioritizing maintenance.
  • Recommendations for corrective action (repair, replacement, or continued monitoring)

Methodology

  • Pre-Test Assessment: Collect equipment history and operating conditions.
  • Testing: Online PD measurement during operation
  • Analysis: Identify the source and severity of PD activity.
  • Discussion: Preliminary findings shared with operations and maintenance teams
  • Reporting: Provide condition assessment, risk level, and recommendations for corrective actions.