DC Resistance Tester Transformer DC Resistance Tester or Loop Resistance Tester



DC Resistance Tester, often referred to as Transformer DC Resistance Tester or Loop Resistance Tester in the power industry, is a precision instrument used to measure the DC resistance value of electrical equipment windings and conductive circuits. It is one of the most basic and critical items in preventive tests and acceptance tests for power equipment. By measuring DC resistance, hidden dangers such as poor contact, welding defects, inter-turn short circuits, and tap changer faults in conductive circuits can be quickly detected. Given that the current time is 2026, such instruments have been fully popularized with functions such as three-phase simultaneous testing, automatic demagnetization, and intelligent diagnosis. 1. Core Functions and Detection Targets The main purpose of DC resistance testing is to check the conductive integrity and connection quality of electrical equipment. Specifically, the following problems can be identified: Transformer Windings: Inter-turn Short Circuits: Short circuits in a few turns within the winding will cause a significant decrease in resistance value. Tap Changer: Poor contact, oxidation, ablation, or incorrect position indication of contacts can cause abnormal resistance in specific gears or three-phase imbalance. Poor Lead Welding: Cold or detached solder joints at the connection points between windings and bushings or leads. Strand Breakage: Broken strands in multi-strand parallel wound conductors. High-Voltage Circuit Breakers/Disconnect Switches: Conductive Circuit Resistance: Detects whether the contact between moving and static contacts is good. If the resistance is too large, it will cause severe heating during operation and may even lead to burnout (usually using a loop resistance tester, with the same principle but larger current). Generators/Motors: DC resistance balance of stator/rotor windings to determine whether there are short circuits or connection errors in the windings. Cables and Busbars: Checks the continuity of long-distance cable conductors or the contact resistance at busbar connection points. 2. Working Principle: Four-Wire Measurement Method (Kelvin Method) To eliminate the influence of test lead resistance and contact resistance on low-resistance measurements, all professional DC resistance testers adopt the four-terminal sensing principle: Current Terminals (C1, C2): The instrument outputs a constant large current (such as 1A, 5A, 10A, or even 40A+) flowing through the object under test. Voltage Terminals (P1, P2): Independently collect the voltage drop at both ends of the object under test. Calculation: According to Ohm's law