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Detection Technology

DC resistance tester measuring transformer

time:2021/5/3   source:华天电力  reading:403 time

The measurement of DC resistance is to check the quality of winding welding and short circuit between windings, whether the tap switch position is correct, etc., and the basic test items after pre-test and tap switch position change are also important inspection items after failure. Under normal circumstances, we often use traditional methods to measure the DC resistance of transformer windings and high-power inductance equipment is a time-consuming and laborious task. In order to change this situation, shorten the measurement time and reduce the workload of the tester, we have developed a A fast DC resistance tester (hereinafter referred to as a DC resistance tester), which is an ideal device for measuring the DC resistance of transformer windings and high-power inductance equipment.


Transformer DC Winding Resistance Tester.png


Therefore, it is necessary to carefully measure the DC resistance to minimize the measurement error. According to regulations, for transformers above 160kVA, the difference between phase resistance and phase resistance is usually less than 2% of the three-phase average value, and the difference between lines is usually less than 1% of the three-phase average value. For transformers of 160kVA and below, the difference between phase resistance and phase resistance is usually less than 4% of the three-phase average value, and the difference between lines is usually less than 2% of the three-phase average value. Compared with the difference between the measurement phases in the corresponding parts, the difference between the measurement phases should not be greater than 2%.


When the measured resistance value of the DC resistance tester exceeds the limit:


(1) First consider whether there is a measurement error (for example, whether an external lead is connected, whether the test lead is too long or too thin, whether the contact is good, whether the battery voltage in the bridge is insufficient).


(2) The resistance value of DC resistance is greatly affected by temperature, so it must be converted to the same temperature (usually 20°C, R20=(T+20)/(T+T), T copper=235). Comparison, and generally based on the oil temperature of the upper layer.


(3) The three-phase distribution transformer currently in use, the high-voltage winding adopts Y-shaped connection, when the resistance value exceeds the limit value, the following formula can also be used [RA=(RAB+rac-rbc)/2, RB=(RAB+) rac-rac)/2, RC(RBC+rac-rab)/2] in order to find the defect phase.


(4) Poor contact of the tap changer leads to high resistance. For example, the switch is clean and electroplated, insufficient spring pressure, uneven stress, and carbon deposits on the overvoltage contacts will cause the resistance to conduct. *end. At this time, the tap changer cover should be opened and rotated several times, usually it can be eliminated.


After the above inspection and treatment, the limit is still exceeded, and the internal fault is likely to be the false welding, welding, disconnection or layer short circuit of the winding and lead wire or the winding burnout.


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