With the continuous upgrading of power equipment predictive maintenance technology, multiple non-intrusive partial discharge detection methods have been widely applied in substation on-site inspection. TEV, UHF, HFCT, AA air-coupled ultrasonic, and AE contact acoustic emission are the five mainstream PD detection technologies. Each method has unique working principles, applicable scenarios, and detection advantages. Choosing the correct detection method according to different equipment can effectively improve the accuracy of partial discharge defect diagnosis.
Working Principle of Each PD Sensor
TEV Transient Earth Voltage
TEV detection technology is specially designed for metal-enclosed switchgear. When partial discharge occurs inside the switchgear, transient electromagnetic pulses will propagate along the metal shell and generate transient earth voltage signals on the equipment surface. The TEV sensor captures these instantaneous voltage pulses to judge the existence of internal partial discharge. It features high sensitivity for closed switchgear defects and is not easily interfered by external environmental noise.
UHF Ultra‑High Frequency
UHF partial discharge detection works by capturing ultra-high frequency electromagnetic waves (300MHz-3GHz) generated by partial discharge. PD faults inside GIS and sealed switchgear will radiate high-frequency electromagnetic signals through insulation gaps and flange gaps. UHF sensors have strong anti-interference ability, which can effectively filter low-frequency on-site interference and realize accurate positioning of internal insulation defects of closed equipment.
HFCT High‑Frequency Current Transformer
HFCT sensors adopt Rogowski coil induction principle, which can be clamped on the grounding wire or shielding layer of power cables and equipment without power failure. Partial discharge will generate high-frequency pulse current in the grounding loop, and HFCT can accurately induce and collect these current signals. It is the most reliable detection method for cable joint and grounding loop PD defects.
AA Air‑coupled Ultrasonic
AA air-coupled ultrasonic detection is a non-contact testing technology. Partial discharge will produce high-frequency ultrasonic vibration signals propagating in the air. The AA focusing probe can remotely capture ultrasonic signals generated by equipment surface discharge and floating discharge. It is suitable for long-distance patrol inspection of outdoor high-voltage equipment and open-type discharge defect detection.
AE Contact Acoustic Emission Sensor
AE contact ultrasonic sensors need to be closely attached to the surface of power equipment. It collects ultrasonic vibration signals transmitted through the equipment shell, which can effectively capture subtle internal discharge signals that cannot be detected by air-coupled probes. It is mostly used for precise defect verification and positioning of switchgear internal discharge.
Sensor Selection Guide by Tested Assets
Sensors for Switchgear PD Test
For medium-voltage metal-clad switchgears, the combination of TEV and AE contact sensors is the preferred solution. TEV quickly screens internal hidden discharge defects, and AE sensors verify and locate fault points accurately. Matching with AA ultrasonic probes can realize full coverage of internal and external discharge detection.
Sensors for GIS Partial Discharge
GIS equipment is fully sealed with metal shell, making ultrasonic detection difficult. UHF sensor is the core detection method for GIS partial discharge, which can capture high-frequency electromagnetic leakage signals of internal defects. Auxiliary ultrasonic detection can assist in secondary verification to eliminate misjudgment.
Sensors for HV Cable Partial Discharge
High-voltage cables and cable joints are prone to insulation aging and breakdown discharge. HFCT sensor clamped on cable grounding wire can stably collect PD pulse current signals, which is the most targeted detection method for cable partial discharge faults.
Sensors for Transformer PD Inspection
Power transformers have complex internal structures. UHF sensors are used to detect internal insulation discharge, and AE contact sensors cooperate to capture vibration signals. The combined detection method effectively identifies floating discharge and tip corona discharge inside transformers.
Multi‑sensor Fusion Advantage for Partial Discharge Detector
Single detection method has obvious limitations and is prone to missed detection and misjudgment. Multi-sensor fusion technology integrates TEV, UHF, HFCT, ultrasonic and other detection modes, which can realize full-scene coverage of different equipment and different defect types. Through cross-verification of multiple signal data, the accuracy of PD defect identification is greatly improved, meeting the comprehensive testing needs of substation predictive maintenance.
MOEORW‑Wi900PD multifunctional partial discharge detector integrates all above sensor interfaces for full‑scene PD testing.
