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# Working Principles of Transformer Winding Resistance Tester

What is the significance of developing a DC winding resistance tester?

is one of the top performance testers specifically made for large motor and power transformer applications, basically, the winding resistance testing is a vital part of the manufacturing quality assurance program and power transformer maintenance. Usually, the large motors and transformers are subjected to overloading, vibrations and environments with high temperature variations, this winding resistance test kit can be used to perform measurements and assure that the connections are made accurately without any shorts or opens. However, winding resistance tester is highly effective to use in finding the tap changer abnormalities, the tap changer of power transformer is especially the most critical element of a power system.

The purpose of the DC winding resistance test is as follows

1. Check the welding quality of the inner wires and leads of the transformer and motor windings. When the welding is not good, it can be judged by the resistance value of the three phases.
2. Check whether the contact of each position of the transformer tap changer is good.
3. Check whether the transformer or motor windings or lead wires are broken.
4. Check the correctness of the parallel branch, whether there is one or several disconnections in the winding formed by several parallel wires.
5. Check whether there is a short circuit between layers and turns of the winding.

How does a DC winding resistance tester work?

The purpose of transformer winding resistance tester can inject a direct current via the windings and also measures the drop of voltage, one of the most challenging tasks in the winding resistance measurement is that voltage across the inductor can be calculated by formula V= L (di/dt), here, L denotes the inductance of winding and (di/dt) denotes the rate of change of current. If there is a small change in the power supply, then it might be caused by poor regulation or ripple, this will make it impossible to measure the direct current resistance.

The major applications of winding resistance tester are given below:

1. Transformer Primary and Secondary Winding Resistance

2. Windings of Motors and Generators

3. PT/CT/CVT

4. Instrument Transformers

5. Voltage Regulators

6. Bus-bar; Cable Line and Swithc Cotact point etc..

The transformer winding resistance tester can always perform measurements on very big transformers for highly filtered and regulated current output.

The 5 most popular manufacturers of DC resistance testers in the world:

Megger winding resistance tester (USA) DV Power winding resistance tester (Sweden) Kingrun winding resistance tester (China)

Hightest winding resistance tester (UK) Raytech winding resistance tester (USA)