Transformer DC Resistance Tester
The transformer DC resistance tester is the core testing equipment for transformer handover, overhaul, and preventive testing. It is mainly used to measure the DC resistance of transformer windings and high-power inductive equipment. It can quickly diagnose hidden faults such as poor winding welding, inter-turn short circuits, poor tap changer contact, and broken leads. It is an essential instrument for ensuring the safe operation of power equipment.
Core Working Principle
Based on Ohm's law (R=U/I), it adopts the four-wire (Kelvin) measurement method:
Apply a constant DC current to the winding through independent current lines
Collect the voltage drop across the winding through independent voltage lines
Built-in high-precision ADC sampling and automatic calculation of resistance value
The four-wire design completely eliminates the influence of lead resistance and contact resistance on measurement results
In response to the characteristics of inductive loads, the instrument also has a magnetic assist/demagnetization function, which can greatly shorten the charging and stabilization time of large transformers.
Core Selection: Match test current according to transformer capacity
This is the most critical dimension in selection, following the principle of "large resistance selects small current, low resistance selects large current":
Transformer Capacity/Type Recommended Test Current Applicable Scenario
PT/CVT transformers, precision coils ≤10mA High-resistance windings
Distribution transformers below 1600kVA 5A～10A Routine distribution operation and maintenance
Medium-sized main transformers 1600～30000kVA 20A～40A 35kV～110kV substations
Large main transformers above 30000kVA 50A and above 220kV and above main transformers
500kV ultra-high voltage/large-capacity power plant main transformers 100A and above Ultra-high voltage/power plants
Low-voltage windings (mΩ level) must use large current (10A+), and high-voltage windings (Ω level) use small current (1A or below).
Parameter Item Conventional Requirements High-precision/Arbitration Grade
Measurement accuracy ±0.2% (±2 digits) ±0.05%
Resolution 1μΩ 0.1μΩ
Measurement range 0.1μΩ～20kΩ Expandable to MΩ level
Output current range Multi-range adjustable (10mA～100A) More than six ranges with fine adjustment
Number of channels Single channel (phase-by-phase measurement) Three-channel synchronous measurement (efficiency ×3)
List of essential functions (hard procurement indicators)
Fully automatic discharge + audible and visual alarm: automatically releases residual charge after testing to eliminate personal safety risks
Back EMF/overcurrent/overvoltage/broken wire protection: resists high-voltage impact at the moment of power failure of inductive loads
Automatic temperature conversion: supports conversion to 75℃ (oil-immersed transformer) or 120℃ (dry-type transformer) standard temperature
Magnetic assist and demagnetization function: mandatory for 110kV and above three-phase five-limb transformers, and automatic demagnetization is required for 220kV and above
Three-phase simultaneous testing: complete three-phase measurement with one wiring for YN-connected transformers, improving efficiency by more than 60%
Data storage and export: ≥500 sets of storage, supports USB flash drive/Bluetooth/RS232 interface
Anti-interference design: stable readings in strong electromagnetic environments of substations, requiring digital filtering and hardware shielding
Type Features Applicable Scenario
Single-channel portable Light weight (≤10kg), built-in lithium battery, simple operation Distribution transformer operation and maintenance, on-site overhaul
Three-channel synchronous Three-phase simultaneous measurement, high efficiency, with unbalance rate calculation 35kV and above main transformers, factory tests
Handheld Ultra-light (1.2～1.7kg), built-in lithium battery with 10h+ battery life High-altitude operations, general testing of distribution areas
Benchtop high-precision 0.05-grade accuracy, laboratory-grade stability Factory inspection, arbitration metrology, research institutes
Local and mainstream manufacturer resources
Based on past selection experience, Jiangsu (especially the Zhenjiang and Yangzhong areas) is the core industrial belt for electric heating equipment in China. It also gathers a large number of qualified manufacturers in the field of power testing instruments. When purchasing, prioritize local industrial belts, which have significant advantages in non-standard customization, after-sales response, and logistics costs.
: GH-6200 inductive load DC resistance tester, supports three-phase simultaneous measurement, automatically adjusts test current, with high-speed printer, resolution 1μΩ, accuracy class 0.2.
Wuhan industrial belt manufacturers (core production area for power testing instruments)
Wuhan Qianxu Electric Power: QXZZ-S10A three-channel DC resistance meter, completes three-phase measurement with one wiring, magnetic assist method compresses large transformer testing time from 40 minutes to 15 minutes, accuracy ±0.2%, 2-year warranty.
Wuhan Guodian Xigao Electric: GDC8000 series DC resistance rapid tester, accuracy up to class 0.05, market share 23.5% in the ultra-high voltage field, significant advantages in projects above 750kV, 28 provincial-level service outlets in China.
Wuhan Ultra-high Voltage Electric Power: adopts "dynamic demagnetization" and "rapid steady-state" technologies, maximum output 100A, suitable for arbitration testing by electric power research institutes and precision factory inspection of large transformers.
Wuhan Chuangyi Electric: CYZRS series, handheld three-channel products with built-in lithium battery lasting 10h+, storing 10,000 sets of data, share exceeding 30% in special industries such as metallurgy/petrochemical/rail transit.
Wuhan Hainuo Paer Electric Power: IP67 protection rating, wide-temperature operation from -40℃ to +70℃, integrating IoT and AI technologies, share exceeding 60% in extreme scenarios such as plateau photovoltaics/desert wind power.
Other well-known brands
Shenyang Dawan Technology (DWKJWORLD): DW8323A accuracy 0.05%, built-in lithium battery for continuous testing of 100+ transformers, weight ≤6kg, suitable for railway traction transformer testing.
Germany SEBA: internationally leading brand, suitable for key projects of multinational grid companies and large energy groups.
Executive Standards
DL/T 845.3-2019: General technical conditions for resistance measurement devices Part 3: DC resistance testers (current electric power industry standard)
GB 6587-86 / GB 6593-86: Relevant national standards for electronic measuring instruments
DL/T 596-1996: Preventive test code for electric power equipment
Precautions for use
Reliable grounding must be done first. The grounding wire must be connected first during test preparation and removed last after work is completed.
It is strictly prohibited to disconnect wires during measurement. Operation is only allowed after the discharge indication ends and the audible and visual alarm stops.
For no-load tap-changing transformers, discharge must be exited before switching the tap changer; for on-load tap-changing transformers, switching can be done directly without discharge.
Non-measured coils need to be short-circuited to reduce electromagnetic interference.
After long-term storage, insulation must be tested before use.
