Why PD Detection Matters
Partial Discharge (PD) is a localized breakdown of insulation that can occur in metal-clad switchgear. Common sites include cable terminations, bus joints, and PT compartments. Left unchecked, PD activity progressively damages insulation and can lead to flashovers, arc faults, and catastrophic failure. Early detection is therefore a critical part of condition-based maintenance.
PD Testing Techniques for Metal-Clad Switchgear
Different methods are used to detect and locate PD in switchgear, each with its own strengths and limitations:
- TEV (Transient Earth Voltage): Portable sensors measure fast voltage transients on the switchgear enclosure. Useful for quick online screening.
- Ultrasonic / Acoustic: Handheld probes detect the “clicks” of PD through vents, seams, and windows. Good for localization.
- HFCT (High-Frequency Current Transformer): Clip-on sensors around ground leads or cable shields capture PD current pulses, suitable for continuous monitoring.
- UHF Sensors (100 MHz–1.5 GHz): Installed in ports or inspection windows, these detect internal PD with high noise immunity.
- IEC 60270 (apparent charge): Offline testing method providing standardized, quantitative measurements (pC).
Because no single method is perfect, combining TEV + ultrasonic for surveys and HFCT/UHF for continuous monitoring is considered best practice.
Designing Switchgear for Easier PD Testing
Most legacy switchgear wasn’t built with PD testing in mind, making surveys and monitoring more challenging. By incorporating simple design features up front, new metal-clad switchgear can be made “PD-ready”:
- Access points: Install ultrasonic/IR windows, UHF feedthroughs, and TEV probe pads at key compartments.
- HFCT accommodation: Provide removable shield-bond test loops for easy clamp-on sensor placement.
- Reference signal: Include a fused VT secondary or capacitive reference jack (BNC) for PRPD synchronization.
- Noise control: Ensure good enclosure bonding with RF gaskets and paint-free bond lands.
- Documentation: Record factory baseline PD levels and provide a labeled test map for consistent field surveys.
These additions make both offline acceptance testing and online monitoring faster, safer, and more repeatable.
Summary
Partial discharge is one of the most reliable early indicators of insulation breakdown in metal-clad switchgear. Using a combination of TEV, ultrasonic, HFCT, UHF, and IEC 60270 testing methods gives the best chance of identifying issues before they become failures. Designing switchgear with PD access and monitoring provisions built in ensures long-term reliability and makes ongoing testing much easier.
High Power Products: PD-Ready Switchgear
At High Power Products, we design and manufacture metal-clad switchgear that is PD-ready by design. Our lineups are engineered with the access points, test loops, and monitoring provisions technicians need for both offline and online PD detection.
If you’re planning a new switchgear lineup or want to explore PD-ready options for your facility, contact High Power Products for a quote.