Specially used for measuring the DC resistance of inductive load windings such as transformers, motors, and mutual inductors



The DC Resistance Tester is the "physical examination instrument" in power equipment maintenance, specially used for measuring the DC resistance of inductive load windings such as transformers, motors, and mutual inductors.

Its core function is to "check for hidden dangers": by accurately measuring resistance values, it determines whether the internal winding wire welding quality is good, whether the tap changer contacts are in good condition, and whether there are defects such as inter-turn short circuits or broken wires.

The following is a detailed analysis compiled in accordance with the latest technical standards (such as DL/T 596-2021):

⚙️ Core Working Principle

The working logic of the DC resistance tester is based on Ohm's law (R=U/I), but to solve the difficulties of on-site measurement, it adopts more advanced technology:

Four-wire measurement method (Kelvin bridge method)

Principle: Two current terminals (C1, C2) output current, and two voltage terminals (P1, P2) collect voltage.

Function: Since almost no current flows through the voltage sampling terminals, the influence of test lead resistance and contact resistance on measurement results can be completely eliminated, ensuring the accuracy of micro-ohm level measurements.

Constant current source technology

The instrument internally generates a stable DC current (such as 1A, 10A, 40A, etc.). For inductive loads (such as transformers), the current takes time to rise, and the constant current source ensures accurate sampling after the current stabilizes.

Anti-interference and demagnetization

Anti-interference: There is 50Hz power frequency interference at substation sites. The instrument eliminates interference signals through filter circuits or frequency conversion technology.

Demagnetization (degaussing): Large transformer cores may retain residual magnetism after testing, which could cause excessive inrush current during commissioning. High-end instruments have an automatic demagnetization function to eliminate residual magnetism after the test.