Partial Discharge

What is Partial Discharge?

Partial discharge (PD) is a localised electrical discharge that occurs when the electric field within an insulating material exceeds its breakdown strength without fully bridging the insulation. Often caused by voids, defects, sharp edges or material interfaces, repeated PD gradually degrades insulation and can eventually lead to equipment failure or complete dielectric breakdown.

PD testing is essential for developing and validating high-voltage equipment such as transformers, switchgear, cables, power electronics and insulation systems. As electrical systems become more compact and operate at higher voltages, understanding PD is increasingly important for improving reliability and extending equipment life.

Imaging Partial Discharge

Partial discharge emits extremely weak (ultraviolet) light over nanosecond to microsecond timescales, making it difficult for conventional high-speed cameras to capture. Intensified imaging overcomes this by isolating the UV spectrum from the image background light by intensification and ultra-fast electronic gating, amplifying the faint optical emissions.

Unlike electrical PD measurements, which can be affected by electromagnetic interference, optical imaging directly reveals where and how discharges develop. Even when PD occurs within solid dielectrics—where UV light is attenuated or down-converted to weak visible wavelengths—high-gain intensified cameras can still isolate these optical signals and enables researchers to visualise corona, streamers and discharge inception with high spatial and temporal resolution.

Lambert Instruments Solutions for Partial Discharge Imaging

Lambert Instruments’ intensified imaging systems are designed specifically for capturing fast, low-light phenomena such as partial discharge, corona and streamer events.

Key benefits include:

High sensitivity for imaging extremely weak optical emissions
Nanosecond electronic gating to freeze fast transient events
Suppression of ambient light and background illumination
Synchronisation with high-voltage excitation for precise event capture
Immunity to electromagnetic interference that can affect electrical PD measurements
Flexible configurations, available as complete intensified cameras or image intensifier attachments for existing high-speed cameras

These capabilities enable researchers to capture discharge events that would otherwise remain invisible using conventional imaging techniques.

Revealing Partial Discharge through Dual-Channel Imaging

This demonstration showcases the benefits of simultaneous UV and visible imaging for the detection and localization of electrical discharges.

The first recording shows the visible emission from an electrical plasma discharge, where the optical signal is weak and often difficult to distinguish from the background using a conventional camera.

The second recording, acquired with the UV-TRiCAM around 300 nm, reveals the characteristic ultraviolet signature of the discharge with high sensitivity and contrast.

Finally, both channels are combined into a single image, providing clear visualization and precise localization of the discharge source while preserving the surrounding scene context. This dual-channel approach enables researchers and engineers to detect, analyze, and pinpoint partial discharge events with greater confidence than visible imaging alone.