A complete offline partial discharge testing system typically includes: High-voltage source: an ozone-free test transformer (generates high voltage with extremely low background noise). Coupling device: coupling capacitor and detection impedance. Measurement main unit: includes preamplifier, filter, data acquisition card, and analysis software. Calibrator: used to inject standard pulses before testing to calibrate the system's sensitivity. Anti-interference system: digital filtering, balance method, etc., to eliminate on-site noise. 5. Difference from "Withstand Voltage Test" The withstand voltage test (using a test transformer) you mentioned earlier is to "assess" whether the insulation can withstand high voltage without breakdown (pass/fail); while the partial discharge test is to "diagnose" whether there are tiny defects inside the insulation. Even if the equipment passes the withstand voltage test, there may still be serious partial discharge hazards. The two are usually used together: first perform non-destructive tests (including partial discharge), and finally perform the withstand voltage test. 6. Purchasing and Usage Suggestions Frequency band selection: Choose based on the type of test object. For transformers and cables, the pulse current method is commonly used; for GIS, the UHF method is preferred; for switchgear inspection, TEV + ultrasonic is commonly used. Anti-interference capability: The on-site environment is complex, so the instrument's digital filtering and noise suppression capabilities are crucial. Positioning function: If the purpose is to locate fault points, confirm whether the instrument has multi-channel synchronous acquisition and time-difference positioning functions. Standard compliance: Ensure the instrument complies with IEC 60270 or GB/T 7354 and other relevant national standards. The Partial Discharge Tester (PD Tester) is an extremely important high-end instrument in the insulation diagnosis of power equipment. It is used to detect weak partial discharge phenomena occurring in the internal insulation structures of high-voltage electrical equipment (such as transformers, GIS, cables, generators, etc.). Partial discharge is an early sign of insulation deterioration. If not handled in time, it will eventually lead to insulation breakdown and equipment failure. Therefore, the partial discharge test is the "stethoscope" for judging the health of equipment insulation. The following is the core knowledge system about the partial discharge tester: 1. Working Principle When partial discharge occurs, extremely short pulse currents are generated inside or on the surface of the insulating medium, accompanied by electromagnetic waves, ultrasonic waves, light, heat, and chemical reactions. The tester mainly captures these signals through the following methods: Pulse Current Method (IEC 60270 standard method): This is the most classic, quantitative standard method. Through the coupling capacitor and detection impedance, the weak discharge signal is converted into a voltage pulse, amplified by the amplifier, and displayed. Advantages: high sensitivity, can quantitatively measure the discharge amount (pC), and results are comparable. Disadvantages: susceptible to on-site electromagnetic interference, requiring good grounding and shielding. Ultra-High Frequency Method (UHF): Mainly applied to GIS (Gas Insulated Switchgear) and transformers. Detects electromagnetic wave signals in the 300MHz-3GHz frequency band generated by partial discharge. Advantages: strong anti-interference capability, suitable for online monitoring, and can perform positioning. Acoustic Emission Method (AE): Detects mechanical vibrations (sound waves) generated by discharge. Advantages: not affected by electromagnetic interference, very suitable for fault location (through acoustic-electric joint positioning). Transient Earth Voltage Method (TEV): Mainly used for live detection of switchgear, detecting transient earth voltages on metal enclosures.