I. Core Technical Principles
The ultrasonic partial discharge tester operates based on the acoustic emission detection technology. When a partial discharge fault occurs inside an electrical equipment, the surrounding medium molecules will undergo intense mechanical collisions and vibrations, thereby generating ultrasonic wave signals with frequencies ranging from 20 kHz to 200 kHz. These signals have good penetrability and can propagate through solid media such as metal casings to the outer wall of the equipment.
The device is equipped with high-sensitivity piezoelectric ceramic sensors. During detection, the sensors are placed on the surface of the equipment, allowing for the precise collection of external ultrasonic wave signals and converting them into electrical signals. After undergoing a series of professional processing such as amplification, filtering, and signal conditioning, the signals are ultimately presented in intuitive forms such as audible sounds, waveform diagrams, and numerical parameters, providing a basis for the detection personnel to assess the equipment’s operating status.
Among various partial discharge detection technologies for power equipment, the core advantage of the ultrasonic method lies in its excellent spatial positioning capability. By collecting signals from multiple points and comparing the amplitude differences of signals from different measurement points, it can accurately determine the specific location of the internal partial discharge fault in the equipment, providing a precise basis for fault diagnosis.
II. Core Application Scope and Engineering Scenarios
(1) Detection of Gas Insulated Full Enclosed Combined Electrical Equipment
Gas insulated full enclosed combined electrical equipment has a compact structure and independent gas compartments. The common insulation defects inside the equipment mainly include free metal particles, fixed protrusions, and insulator surface dirt, and the application of ultrasonic partial discharge detection technology in this type of equipment detection has been very mature and reliable.
Typical application method: The detection personnel place ultrasonic sensors at key points such as the inspection manholes and flange joint surfaces of the equipment shell, collect the ultrasonic signals during equipment operation, and conduct a comprehensive search for potential faults.
Typical signal characteristics: When free metal particles inside the equipment are subjected to the electric field, they will jump randomly and have a strong amplitude fluctuation, resulting in a characteristic signal of strong randomness and large amplitude fluctuation; when the equipment has a tip discharge fault, it will present a continuous pulse signal characteristic highly correlated with the power frequency phase.
Engineering value: This detection method is not limited by the layout of the transparent window of the insulator disk in the pot-type insulator of the equipment and can be carried out at any position on the metal shell surface, having extremely strong adaptability. It is particularly suitable for old equipment and equipment without built-in detection sensors, effectively overcoming the limitations of traditional detection methods.
(2) Detection of Air Insulated Metal Enclosed Switchgear
The internal space of air insulated metal enclosed switchgear is narrow, and insulation faults are more likely to occur in core parts such as the handcart contacts, insulating barriers, and wall-through bushings. The ultrasonic detection method mainly conducts detection on two typical faults in the air gap of the equipment: corona discharge and surface discharge.
Typical application method: It can be carried out in a comprehensive coverage scan along the gaps between the panel and the observation window and other non-metallic areas, or the sensor can be directly attached to the metal cabinet surface for precise定点 detection.
Typical signal characteristics： The amplitude of the ultrasonic wave signal generated by slight corona discharge is relatively weak， with a dispersed pulse as the main characteristic； when the equipment has a severe discharge fault， it will present a regular “sizzling” or “popping” sound， with extremely high signal recognition degree.
Engineering value： In the daily inspection of switch cabinets， the ultrasonic method can be used in conjunction with the transient ground voltage method to form an efficient inspection system. The transient ground voltage method completes a large-scale rapid screening to lock in the suspected fault points， and then the ultrasonic method is used to accurately verify and locate the abnormal points， significantly improving the inspection accuracy and efficiency.
(3) Detection of Oil-Immersed Transformers
The internal insulation structure of oil-immersed transformers is complex， and partial discharge faults can occur in the oil-paper composite insulation parts such as the winding turns， leads， and pressure plates. Due to the influence of the oil medium, the ultrasonic signal will experience certain attenuation when propagating in the oil, which poses certain challenges to the detection work. However, this technology remains one of the core means for locating internal discharge faults in transformers.
Typical application method: Place the sensor at different heights and directions on the outer wall of the transformer oil tank. Through multi-channel signal synchronous acquisition technology, accurately calculate the three-dimensional coordinates of the discharge point inside the equipment to achieve precise fault location.
Typical signal characteristics: The ultrasonic signal generated by local discharge in the transformer oil has a short rise time and its spectrum mainly falls within the 80kHz–200kHz range. It can be effectively distinguished from the mechanical vibration signals of the equipment within the range of 50Hz–1kHz, avoiding misjudgment caused by signal interference.
Engineering value: When the oil chromatography analysis detects fault gases such as acetylene and determines that the equipment is abnormal, the ultrasonic detection method can further confirm whether there is a discharge fault inside the equipment and accurately locate the fault position. This provides precise guidance for subsequent oil drainage inspection, opening the cover for maintenance, and other operation and maintenance work, avoiding blind maintenance operations, reducing operation and maintenance costs, and improving maintenance efficiency.
(4) Detection of power cable terminals and joints
Power cable terminals and intermediate joints are the weak links in power line operation, with a high occurrence rate of faults. The ultrasonic detection method is mainly used to investigate insulation interface air-gap discharge faults in outdoor terminals and intermediate joints of cables.
Typical application method: Use the contact detection method to conduct comprehensive detection along key prone-to-fault parts such as the root of the cable terminal umbrella skirt and the shell of the joint.
Typical signal characteristics: The ultrasonic signal generated by the air-gap discharge inside the cable accessory is affected by the insulation medium and has a complex propagation path, resulting in a relatively low overall amplitude. However, its signal characteristics are stable and repeatable, making it easy to identify and analyze faults.
Engineering value: It can be combined with infrared thermography detection data to multi-dimensionally determine whether there is a discharge-induced heating fault inside the cable joint, effectively avoiding the limitations of a single detection method and improving the accuracy of fault detection for cable accessories.
III. Core Technical Points for Equipment Selection
Based on the detection scenarios and fault characteristics of different power equipment, the selection of ultrasonic partial discharge testers needs to focus on the following core technical parameters and functions, to meet the requirements of different engineering detection needs.
1. Detection frequency band: The frequency spectrum characteristics of fault ultrasonic signals of different equipment vary, so targeted selection is required. Gas-insulated fully enclosed combined electrical apparatus is suitable for a frequency band of 20kHz–80kHz; oil-immersed transformers are suitable for a frequency band of 80kHz–200kHz; air-insulated switch cabinets and cable terminals are suitable for a frequency band of 20kHz–60kHz. Wide-band equipment has a wider scene adaptability, but it requires higher requirements for equipment signal processing algorithms and hardware performance.
2. Measurement range: The conventional effective measurement range is from –7dBμV to 68dBμV. This range can fully cover the entire stage of fault signals from weak corona discharge to intense arc discharge, ensuring that all degrees of discharge faults can be effectively detected.
3. Auxiliary functions: It needs to be equipped with an external difference frequency conversion function, which can convert high-frequency ultrasonic signals into audible sounds, facilitating on-site detection personnel to quickly and intuitively judge the fault state; it is equipped with a phase synchronization interface, which can precisely analyze the correlation characteristics of the discharge signal and the power frequency, effectively distinguish interference signals from fault signals, and improve the accuracy of fault identification.
4. Comprehensive detection capability: For precise fault diagnosis scenarios of equipment, an integrated test equipment that integrates multiple detection technologies can be selected. Through the complementary integration of multiple technologies, it can make up for the shortcomings of the sensitivity of single ultrasonic detection method to small air-gap discharge, and comprehensively improve the accuracy and comprehensiveness of fault detection and diagnosis.
Post time: Jun-05-2026