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Precautions for transformer DC resistance tester

time:2020/8/16   source:华天电力  reading:265 time

The transformer DC resistance tester is an important item in the transformer test. Through measurement, it is possible to check whether the conductive circuit of the equipment has defects such as poor contact, poor welding, coil failure, and wiring errors. In the actual measurement of medium and small transformers, most of the DC bridge method is used. When the resistance value of the tested coil is above 1 ohm, it is generally measured with a single-arm bridge, and when the resistance value of the tested coil is below 1 ohm, it is measured with a double-arm bridge. When using double-arm bridge wiring, the potential pile head of the bridge should be close to the measured resistance, and the current pile head should be connected to the potential pile head.

 

Transformer DC Winding Resistance Tester.png


Before the measurement, the transformer DC resistance tester should first estimate the resistance value of the tested coil, place the bridge magnification button in the appropriate position, short-circuit the non-tested coil and ground, then turn on the power switch to charge, and press it after fully charged The galvanometer switch quickly adjusts the measuring arm to make the galvanometer pointer move to the zero line in the middle of the galvanometer scale for fine adjustment. When the pointer stops at the zero position, the resistance value is recorded. At this time, the measured coil Resistance value=multiplying factor×measurement arm resistance value. After the measurement is completed, first open the galvanometer button, and then release the power switch.


Precautions for transformer DC resistance tester

 

In the measurement process, in addition to strictly complying with the electrical safety regulations and equipment test regulations, special attention should also be paid to:

 

1) Measure when the temperature of the coil is stable, and the temperature difference between the upper and lower parts of the transformer tank should not exceed 3°C;

 

2) Due to the inductance of the transformer coil, the charging current during measurement is not stable. You must count after the current is stable. If necessary, measures to shorten the charging time shall be taken;

 

3) Minimize the contact resistance of the wires in the test circuit. The transformer taps in operation are often affected by oil film and other contaminants to make their contact poor. Generally, it is necessary to switch several times before measuring to avoid discrimination errors;

 

4) When measuring the low-voltage side of the transformer, all personnel should keep a proper safe distance from the high-voltage side;

 

5) The instrument should be protected from strong vibration, direct sunlight and magnetic field during transportation, storage and work. When storing and storing the instrument, pay attention to the ambient temperature and humidity. It should be placed in a dry, ventilated, and non-corrosive place. When exposed to damp, rain, or sun, handle with care, and do not fall.

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