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Abnormality of voltage transformer

time:2021/1/17   source:华天电力  reading:230 time

Judgement of common abnormalities of voltage transformer of DC resistance tester:


(1) Three-phase voltage indication is unbalanced: one phase is reduced (it can be zero), the other two phases are normal, the line voltage is abnormal, or accompanied by sound or light signals, it may be a high-voltage or low-voltage fuse blown.


(2) Neutral point is not effectively grounded system, three-phase voltage indication is unbalanced: one phase decreases (may be zero), the other two phases increase (up to line voltage) or pointer swings, it may be a single-phase grounding fault or base Frequency resonance, if the three-phase voltage rises at the same time and exceeds the line voltage (the pointer can swing to the top), it may be frequency division or high-frequency resonance.


Transformer DC Winding Resistance Tester.png


(3) If the high-voltage fuse is blown repeatedly, the internal insulation may be seriously damaged, such as a short circuit between winding layers or turns.


(4) Neutral point effective grounding system. When the bus is switched on, the phase voltage rises and swings at low frequency, which is generally a series resonance phenomenon; if there is no operation, the phase voltage suddenly rises or drops abnormally, it may be The internal insulation of the transformer is damaged, such as the short circuit fault of the insulation bracket winding, the winding layer or the turn.


(5) The neutral point is effectively grounded. When the voltmeter is in operation, the indication of the voltmeter is unstable, which may be due to poor grounding of the high voltage winding N(X) terminal.


The DC resistance tester is a high-precision replacement product for DC single and double-arm bridges. The DC resistance fast tester adopts advanced switching power supply technology, and the measurement result is displayed by a dot matrix LCD. It overcomes the shortcomings of other similar products that the LED display value is inconvenient to read in the sun, and it has the automatic arc suppression function. The DC resistance test of the transformer winding is an indispensable test item after the transformer is handed over, overhauled, and tap changer changed. Under normal circumstances, using traditional methods (bridge method and voltage drop method) to measure the DC resistance of transformer windings and high-power inductive equipment is a time-consuming and labor-intensive work. In order to change this situation, shorten the measurement time and reduce the workload of testers.

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