A Transformer DC Resistance Tester is a very important and commonly used specialized instrument in the power industry, electrical equipment manufacturing, and maintenance.
Simply put, its core purpose is to accurately and quickly measure the DC resistance of various electrical equipment (especially inductive equipment).
1. Core Functions and Measurement Objects
Its main task is to measure the DC resistance of windings, such as:
Power transformers: Phase-to-phase resistance of all windings, as well as various tap positions of on-load tap changers.
Motors: Three-phase windings and rotor windings.
Instrument transformers (CT/PT): Primary and secondary winding resistance.
Switches and circuit breakers: Contact resistance of conductive circuits.
Cables and wires: Resistance of entire or segmented conductors.
2. Why Measure DC Resistance? (Its Importance)
Measuring DC resistance is a fundamental method for inspecting the internal quality and assessing the condition of electrical equipment. The main purposes include:
1.Checking for inter-turn/inter-layer short circuits in windings: This is one of the most critical uses. If a transformer or motor winding experiences a short circuit in a few turns, its DC resistance value will change slightly. Precise measurement and comparison with factory values, historical data, or identical windings can detect this potentially serious fault.
2.Assessing wire connections and contact integrity: Checking whether the contact resistance at connection points such as solder joints, bushing leads, and switch contacts is too high. Poor contact can cause localized overheating, posing a significant safety risk during equipment operation.
3.Judging three-phase balance: For three-phase equipment (e.g., transformers, motors), comparing the DC resistance values of the three-phase windings can determine whether they are balanced. Imbalance may indicate the aforementioned short circuits or connection issues.
4.Calculating average winding temperature rise: In temperature rise tests, the change in DC resistance between cold and hot states is used to calculate the average temperature of the windings.