Partial Discharge Tester (abbreviated as PD Tester) is an extremely important high-end instrument in insulation diagnosis of power equipment. It is used to detect weak partial discharge phenomena occurring inside the insulation structure 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, partial discharge testing is the "stethoscope" for judging the insulation health of equipment. The following is the core knowledge system about partial discharge testers: 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 and quantitative standard method. Through coupling capacitors and detection impedances, weak discharge signals are converted into voltage pulses, amplified, and displayed. Advantages: high sensitivity, quantitative measurement of discharge magnitude (pC), and comparable results. 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. It 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 location. Ultrasonic Method (AE): Detects mechanical vibrations (sound waves) generated by discharge. Advantages: immune to electromagnetic interference, very suitable for fault location (through acoustic-electric joint location). Transient Earth Voltage Method (TEV): Mainly used for live detection of switchgear, detecting transient earth voltages on metal enclosures. 2. Main Application Scenarios Transformers: Detect defects inside windings and oil-paper insulation (such as bubbles, impurities, floating potentials). Usually combined with Dissolved Gas Analysis (DGA). GIS (Gas Insulated Switchgear): Due to the compact internal space of GIS, partial discharge is extremely harmful, and the UHF method is its main detection means. High-voltage cables: Detect insulation defects in the cable body and accessories (terminations, joints), commonly used in factory tests and acceptance tests. Rotating machines (generators/motors): Detect insulation aging of stator windings. Instrument transformers, bushings, surge arresters, and other high-voltage components. 3. Key Test Indicators Apparent Discharge Magnitude (q): Unit pC (picocoulomb), the core indicator measuring discharge intensity. Partial Discharge Inception Voltage (PDIV): The minimum voltage at which partial discharge begins to occur. Partial Discharge Extinction Voltage (PDEV): The maximum voltage at which partial discharge disappears when the voltage is reduced. Phase-Resolved Partial Discharge (PRPD) Pattern: The most important function of modern instruments. By analyzing the correspondence between discharge signals and power frequency voltage phase, two-dimensional or three-dimensional patterns are generated to identify discharge types (such as internal void discharge, surface discharge, floating discharge, corona discharge, etc.). 4. Test System Composition A complete offline partial discharge test system typically includes: High-voltage source: Corona-free test transformer (generates high voltage with extremely low background noise). Coupling device: Coupling capacitor and detection impedance. Measurement host: 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, balanced method, etc., to eliminate on-site noise. 5. Difference from "Withstand Voltage Test" The withstand voltage test you mentioned earlier (using a test transformer) is to "assess" whether the insulation can withstand high voltage without breakdown (pass/fail); while partial discharge testing 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 PD), and finally perform the withstand voltage test. 6. Selection and Usage Suggestions Frequency band selection: Choose according to the type of test object. Transformers and cables commonly use the pulse current method; GIS prefers the UHF method; switchgear inspection commonly uses TEV + ultrasonic. Anti-interference capability: The on-site environment is complex, and the instrument's digital filtering and noise suppression capabilities are crucial. Location function: If the purpose is to find fault points, confirm whether the instrument has multi-channel synchronous acquisition and time-difference location functions. Standard compliance: Ensure the instrument complies with IEC 60270 or GB/T 7354 and other relevant national standards. Are you interested in specific test wiring methods, how to analyze PRPD patterns, or partial discharge test solutions for specific equipment (such as transformers or cables)? Please let me know your specific needs.