1. Core Working Principle
When partial discharge occurs, it produces various physical effects. The tester captures these signals to locate and quantify defects:
Electrical pulse signals: High-frequency current pulses generated at the moment of discharge (main detection method).
Electromagnetic wave radiation: UHF (300MHz-3GHz) electromagnetic waves generated by discharge.
Acoustic wave vibration: Ultrasonic signals generated by discharge (frequency typically 20kHz-300kHz).
Optical radiation: Weak light accompanying some gas discharges (less commonly used in routine testing).
Testing process: Sensor acquisition → Preamplifier filtering and amplification → High-speed A/D sampling → Digital signal processing (denoising, feature extraction) → Pattern recognition (AI algorithm determines defect type) → Report generation.
2. Main Detection Technologies and Methods
A. Electrical Method (Pulse Current Method - IEC 60270 Standard)
Principle: Measures the pulse current generated across the test object using coupling capacitors and detection impedance.
Advantages: Quantitatively accurate (unit: pC), and is the benchmark method for factory and type tests.
Disadvantages: Weak anti-interference capability, requiring shielding rooms or complex on-site noise reduction; limited transmission distance for low-frequency signals.
Applicable to: Factory tests and laboratory precision measurements of transformers, instrument transformers, and cables.
B. Ultra-High Frequency Method (UHF Method)
Principle: Uses built-in or external antennas to receive 300MHz-3GHz electromagnetic waves generated by PD.
Advantages: Extremely strong anti-interference capability (avoids low-frequency grid noise), very high sensitivity, suitable for online monitoring and GIS (Gas-Insulated Switchgear) detection.
Disadvantages: Difficult to directly calibrate to pC values (usually expressed in dBm or relative amplitude), requiring the establishment of correlation models.
Applicable to: GIS/GIL, transformers, high-voltage cable terminations.
C. Acoustic Emission Method (AE Method)
Principle: Uses piezoelectric sensors in contact with the equipment enclosure to receive mechanical vibration waves generated by PD.
Advantages: Precise location (via time-difference of arrival), immune to electromagnetic interference, and can distinguish internal discharge from surface discharge.
Disadvantages: Signals attenuate quickly in solids/liquids, short detection distance, requiring multi-point deployment.
Applicable to: Transformer tanks, GIS enclosures, cable joint location.
D. High-Frequency Current Transformer Method (HFCT Method)
Principle: Clamp-on sensors are attached to grounding wires to sense high-frequency current signals.
Advantages: Non-invasive, easy installation, no power outage required (online detection), suitable for cables and rotating machines.
Applicable to: High-voltage cables, generator/motor stator windings.
3. Technology Development Trends and Characteristics in 2026
Current partial discharge testers have evolved significantly compared to a few years ago:
Multi-sensor Fusion: Single methods are prone to misjudgment; modern instruments integrate UHF + AE + HFCT + TEV (Transient Earth Voltage) modules simultaneously.
The system automatically synthesizes multiple signal characteristics, greatly improving the accuracy of defect identification (>95%).
AI Intelligent Diagnosis and Pattern Recognition: Built-in deep learning algorithms automatically analyze PRPD patterns (Phase-Resolved Partial Discharge patterns).
It can automatically identify typical defect types: internal void discharge, corona discharge, floating potential discharge, surface discharge, and provide confidence scores.
It has a "self-learning" function, and its recognition capability continuously improves as the database updates.
