The core function of the DC resistance tester is to measure the DC resistance of winding conductors to determine:
Welding quality: Whether the internal wire joints and lead connections of the winding are properly welded.
Tap changer status: Whether the contacts of on-load or off-circuit tap changers are tightly engaged, and whether there is oxidation or arcing.
Inter-turn short circuits: Although mainly detected by turns ratio and induced voltage tests, severe inter-turn short circuits can also cause abnormal resistance readings.
Three-phase balance: Check whether the resistance unbalance rate of the three-phase winding exceeds the standard (usually required to be ≤1% or 2%).
Based on the latest technical standards for 2025-2026 (such as DL/T 845.2-2019, GB 1094.1) and market applications, here is a detailed guide:
1. Core Technology Evolution and Functional Highlights
Traditional single-channel testing requires phase-by-phase measurement, and after each phase change, it is necessary to wait for the inductor to discharge (which may take several minutes), resulting in extremely low efficiency. Modern instruments have been fully upgraded to multi-channel, fast demagnetization, and intelligent analysis types:
Three-phase simultaneous testing: High-end models can output three currents simultaneously to measure three-phase resistance, reducing test time from 30 minutes to 3-5 minutes.
Fast demagnetization technology: Uses constant current source reverse demagnetization or sudden current change method to quickly eliminate the huge magnetic field energy in the winding after the test, compressing the discharge waiting time from several minutes to a few seconds, greatly improving efficiency and protecting equipment.
High-precision constant current source: Output current is stable (1A, 5A, 10A, 20A, 40A, 50A, or even 100A optional), can penetrate contact resistance and truly reflect the conductor condition.
Automatic tap position recognition: With on-load tap changers, it can automatically scan all tap positions and plot a "resistance-tap position" curve to quickly locate switch faults.
Temperature conversion: Built-in temperature sensor or manual input of oil temperature, automatically converts the measured resistance value to a standard temperature (such as 75°C or 20°C) to directly determine whether it is qualified.
Anti-interference capability: Equipped with powerful digital filtering for strong electromagnetic environments on site.
2. Mainstream Brands and Market Landscape in 2026
The domestic market is still dominated by the Wuhan industrial cluster, with extremely high technical maturity, fully meeting the bidding requirements of State Grid and China Southern Power Grid.
Leading domestic brands (highly recommended)
Wuhan UHV Electric Power Technology Co., Ltd.:
Status: Industry benchmark, its DC resistance tester is known for "fast test speed" and "thorough demagnetization".
Core technology: Unique intelligent waveform analysis algorithm that accurately determines the inductor stability point, avoiding errors caused by premature readings; high synchronization in three-phase testing.
Features: Large touch screen operation, built-in expert diagnostic database, automatically judges three-phase unbalance rate and alarms; supports USB/Bluetooth report export.
Applicability: Full scenario from 10kV distribution transformers to 1000kV UHV transformers.
Wuhan Huadian Keyi / Wuhan Weian Electric Power:
Features: Established manufacturers, products are durable and cost-effective. Provide various specifications such as single-phase, three-phase, portable, and vehicle-mounted.
Advantages: After-sales service network covers the whole country, free software upgrades, suitable for grassroots power supply stations and engineering companies.
Yangzhou Tuopu / Shanghai Shengxu:
Features: Focus on portability design, suitable for field, high-altitude, or space-constrained substation operations.
International well-known brands
Austria OMICRON (MPDC series), USA Megger (MTO series):
Features: Exquisite craftsmanship, good long-term stability, with extremely high resolution (0.1μΩ) and advanced diagnostic functions (such as demagnetization curve analysis).
Disadvantages: Expensive (usually 5-10 times the price of domestic products), complex operating logic.
Applicability: Provincial electric power research institutes, ultra-high voltage bureaus, research institutions, and foreign-related projects with strict brand requirements.
