to prevent residual charge from damaging the instrument or causing injury. Wiring Sequence: First connect the ground wire (E terminal), then the current leads (C1/C2), and finally the voltage leads (P1/P2). For on-load tap changer testing, ensure no power interruption during switching (some high-end instruments support testing without power interruption). Wait for Stability: Although modern instruments are fast, still observe the current stability indicator. For giant transformers, if using old equipment, do not take readings before stabilization. Discharge Confirmation: After the instrument indicates "discharge complete" at the end of the test, it is still recommended to use a dedicated discharge rod to manually discharge the test object again to ensure safety. Temperature Recording: Be sure to record the top oil temperature or winding temperature during the test; otherwise, data cannot be compared longitudinally. 6. Market Leading Brands (2026 Reference) International Brands: Omicron (Austria): Its MPRO series is renowned for extremely high precision and powerful tap changer waveform analysis software, setting the benchmark in the global high-end market. Megger (UK): The DLRO series enjoys a strong reputation in low-resistance testing, being robust and durable. Leading Domestic Brands: Wuhan Haomai Electric, Wuhan Huatian Electric, and the instrument factory under Baoding Tianwei Group: Domestic equipment has surpassed imported products in three-phase simultaneous testing speed and cost-effectiveness. Especially in optimization algorithms for large transformer structures unique to China's power grid, they perform exceptionally well. Shanghai Sute Electric: Has unique advantages in portable and explosion-proof DC resistance testers. 7. Quick Reference for Common Fault Diagnosis: Three-phase resistance imbalance rate exceeding standard: If a certain phase resistance is significantly higher → → poor contact of the tap changer in that phase, lead breakage, or cold solder joint. If a certain phase resistance is significantly lower → → there may be severe inter-turn short circuit (rare, usually accompanied by other characteristics). Abnormal tap changer waveform: Waveform shows "spikes" or "breakpoints" → → contact bounce or open circuit at the moment of contact. Transition time too long/short → → mechanical mechanism sticking or spring fatigue. If you need test plans for specific capacity transformers (such as "1000kV UHV transformer" or "wind power box transformer"), or need to understand specific national standard criteria (such as the imbalance rate regulations in GB 50150-2016), please let me know, and I can provide more detailed guidance. Main Application Scenarios: Power Transformers: Factory tests: Verify winding conductor specifications and welding quality. Handover/preventive tests: Detect whether tap changer contacts are in good condition (most common fault point) and investigate inter-turn short circuits. Generators and Motors: Measure stator winding DC resistance to determine strand breakage or poor welding. Measure rotor winding resistance to evaluate slip ring contact condition. GIS and Circuit Breakers: Measure contact resistance of main circuit conductive rods and contacts (usually requires a high-current micro-ohmmeter, but the principle is the same). Cables and Busbars: Detect continuity and phase balance of long-distance cable conductors.
