Partial Discharge Tester (referred to as "PD tester") is a precision instrument used to detect partial discharge (PD) phenomena in insulation systems of high-voltage electrical equipment. Partial discharge is an early sign of insulation deterioration. If not detected and addressed in time, it can gradually develop into penetrating breakdown, leading to equipment explosion or power grid outages. Therefore, the PD tester is hailed as the "CT scanner" or "stethoscope" for power equipment, serving as a core diagnostic tool to ensure the safe operation of the power grid. 1. Core Working Principle Partial discharge generates various physical effects, and the PD tester captures these signals to locate and quantify defects: Electrical measurement method (pulse current method): Based on GB/T 7354 / IEC 60270 standards. It detects transient pulse current signals generated by discharges. This is the benchmark method for quantitative measurement, offering the highest accuracy (up to pC level), mainly used for factory tests and acceptance tests. Ultra-high frequency method (UHF): Detects electromagnetic wave signals from discharges in the 300MHz~3GHz range. It has strong anti-interference capability and is mainly used for online monitoring and live detection of GIS (gas-insulated switchgear) and transformers. Acoustic emission method (AE): Detects mechanical vibration sound waves (20kHz~300kHz) generated by discharges. It is mainly used for locating discharge points, particularly suitable for surface discharge detection in switchgear and cable terminations. Transient earth voltage method (TEV): Detects transient earth voltages induced on the metal enclosure of switchgear due to internal discharges. It is the preferred method for live inspection of switchgear in distribution rooms. High-frequency current transformer method (HFCT): Couples high-frequency current signals on cable grounding wires through clamp-on sensors, commonly used for online monitoring of cables. Modern high-end instruments typically adopt "multi-principle fusion" technology, simultaneously collecting electrical, acoustic, optical, UHF, and other signals to improve diagnostic accuracy through joint analysis. 2. Main Application Scenarios Transformers: Detecting inter-turn insulation defects in windings, oil-paper insulation defects, and floating potential discharges. GIS/GIL: Detecting free metal particles, tip discharges, and surface contamination or cracks on insulators. Power cables: Detecting insulation aging or installation process defects (such as improper semiconductor layer stripping) in cable bodies, intermediate joints, and terminations. High-voltage switchgear: Live detection of discharges caused by aging internal insulation components or poor contact. Instrument transformers, bushings, capacitors: Factory type tests and preventive tests. 3. Mainstream Technical Features and Standards for 2025-2026 With the tightening of standards such as GB/T 7354-202X (new revision in progress), DL/T 417-2025 (Guidelines for On-site Measurement of Partial Discharge in Power Equipment), and the development of smart grids, current PD testers show the following trends:
- Manufacturers/Laboratories (type tests): Must choose a pulse current method PD tester compliant with GB/T 7354 / IEC 60270, requiring high accuracy (0.1pC resolution) and authoritative calibration sources.
- Substations/Field Maintenance (live detection): Prefer multifunctional portable PD testers integrating TEV + ultrasonic + UHF functions, with strong anti-interference capability, suitable for inspection of switchgear, GIS, and transformers.
- Special cable testing: Choose dedicated cable PD test systems equipped with high-frequency current transformers (HFCT) and capacitive couplers, supporting oscillating wave (OWTS) test technology (if conditions permit).
- Online monitoring systems: Choose fixed online monitoring devices that support IoT transmission and have edge computing capabilities (preliminary front-end diagnosis).
