Ultrasonic partial discharge detection technology is a mature non-disruptive diagnostic method for power equipment. Its physical basis originates from the acoustic effect accompanying the partial discharge phenomenon. When insulation defects occur inside high-voltage electrical equipment and lead to partial discharge, the surrounding oil, gas, and solid insulators will instantly absorb energy, undergo rapid expansion and contraction, and generate broadband mechanical wave signals. These signals are mainly distributed in the 20 kHz – 300 kHz ultrasonic frequency band. They are collected by high-sensitivity piezoelectric sensors attached to the equipment shell and then processed through signal amplification, filtering, analog-to-digital conversion, and converted into analyzable electrical parameters.
Ultrasonic waves are mechanical waves. Compared with pulse current methods and high-frequency electromagnetic wave detection methods, it is almost immune to the strong electromagnetic fields in substations, and has better measurement signal-to-noise ratio and data repeatability. This technology can conduct online detection at the rated operating voltage of the equipment without planned power outages, ensuring power reliability and providing important data support for equipment condition maintenance.
Core functions and application advantages
In engineering sites, the ultrasonic partial discharge detector is equivalent to the “acoustic stethoscope” of the equipment. The core advantages mainly include three points:
Outstanding anti-electromagnetic interference ability: In complex electromagnetic environments with high voltage and large current, such as UHF (Ultra High Frequency) and TEV (Transient Earth Voltage) signals, which are electrical signals, are prone to be interfered by external noise. Ultrasonic waves, being mechanical waves, inherently possess electromagnetic immunity characteristics. The detection results are true and reliable, and are particularly advantageous in substations with densely arranged GIS (Gas Insulated Switchgear) and switch cabinets.
All-condition live detection capability: The detection operation does not require equipment to be shut down or adjustment of equipment operation mode. It can be applied in various scenarios such as daily inspections, regular maintenance, and troubleshooting of sudden faults, reducing power outage losses and lowering operation and maintenance costs.
Accurate sound source location function: Ultrasonic waves have strong directionality in the transmission through metal shells and air. Staff can use multi-point amplitude comparison or time difference positioning methods to control the spatial error of the discharge location within a few centimeters within a detection range of several meters, providing clear guidance for on-site precise elimination of equipment defects.
Key technical indicators and selection criteria
During the selection and equipment acceptance stage, the following core performance indicators need to be focused on to ensure the validity of the detection data:
Detection sensitivity: Sensitivity represents the instrument’s ability to identify weak discharge signals. According to DL/T 1416 – 2015 “General Technical Conditions for Ultrasonic Partial Discharge Testers”, the ultrasonic detection sensitivity should generally not be lower than 20 dBμV, corresponding to an equivalent discharge quantity of approximately 5 pC. High-performance equipment has lower background noise and is more suitable for operation sites with high background noise.
Effective detection frequency band: The working frequency band of the instrument needs to match the main energy range of the partial discharge ultrasonic signals. Market mainstream instruments cover 20 kHz – 300 kHz, and some high-end models can expand to 500 kHz to collect higher-frequency signals for distinguishing different types of discharge sources.
Anti-interference and signal processing capabilities: High-performance equipment integrates digital filtering, phase windowing, and wavelet denoising algorithms, which can filter out corona interference, mechanical vibration noise, and environmental noise, extracting true partial discharge characteristic signals in complex sites.
Technical limitations and comprehensive diagnosis suggestions
The ultrasonic detection method has certain applicable boundaries. If the discharge location is deep within the equipment or completely enclosed in a metal cavity, ultrasonic waves will significantly attenuate when passing through the interfaces of solid-gas and solid-liquid media. Weak partial discharge signals may be masked by noise. For important equipment or suspicious defect re-examinations, other partial discharge detection methods should be combined for comprehensive judgment. Common combination schemes include:
Ultrasonic method + UHF (Ultra High Frequency) method: Used for large enclosed equipment such as GIS (Gas Insulated Switchgear) and transformers, combining the ultrasonic positioning ability and the high sensitivity detection characteristics of UHF to achieve complementary advantages.
Ultrasonic method + Transient Electromagnetic Wave (TEV) method: Applied to medium-voltage switch cabinets. TEV is used for large-scale rapid screening, followed by ultrasonic for reconfirmation and more precise positioning.
By cross-comparing multiple physical detection methods, the accuracy of discharge type identification can be improved, the credibility of defect severity assessment can be enhanced, and a complete judgment basis for the insulation status evaluation of power equipment can be provided.
Post time: Sep-15-2026