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Two methods of measuring transformer windings

time:2021/3/4   source:华天电力  reading:297 time

The purpose of the DC resistance tester to measure the DC winding resistance of the transformer windings is to check the welding quality of the winding joints and whether there is a short circuit between the windings, whether the contact position of the voltage tap switch is good, whether the actual position of the tap matches; whether the wire is broken or twisted When the combined wires and windings are broken, when the transformer is overhauled, or after the tap position is changed, or after the outlet is short-circuited, it is necessary to measure the DC winding resistance of the winding and the bushing.


Transformer DC Winding Resistance Tester.png


The measuring method of the transformer DC resistance tester is as follows:


(1) Current, voltmeter method, also known as voltage drop method, the principle is to measure the voltage drop on the resistance through direct current in the measured resistance, and calculate the measured resistance value according to Ohm's law, due to the internal of the ammeter and the voltmeter Resistance will affect the measurement results, so carefully consider how they are connected to the measurement circuit.


(2) Balanced bridge method, which is a method of measuring the resistance of DC windings using the principle of bridge balance. Commonly used balanced bridges are single-arm bridge and double-arm bridge. The transformer DC resistance tester is measuring the DC winding of the transformer. For resistance, it should be performed after the transformer is powered off and the high-voltage wire is removed. For large-scale large-capacity power transformers, the charging time constant τ of the rl series circuit is very large, which makes it take a long time for each measurement to wait for the current and voltmeter to indicate It is stable, so the work efficiency is very low, and special instruments (such as constant current) are often used, replacing the power supply in the test with a power supply, which can greatly reduce the test time. The standard for measuring the DC winding resistance of the transformer coil is: for transformers above 1600 kva , The resistance difference of each phase winding should not exceed 2% of the three-phase average value, and the neutral line should have no winding point lead wire, and the difference between the lines should not be greater than 1% of the three-phase average value. For 1600kva and For the following transformers, the difference between the phases is generally not more than 4% of the three-phase average, and the difference between the lines is generally not more than 2% of the three-phase average. Compared with the measured value of the previous part, the change should not exceed 2%, and the neutral lead wire should not be wound, the difference between the wires should not be greater than 1% of the average value of the three phases. For transformers of 1600kva and below, the difference between the phases is generally not greater than the average value of the three phases. %, the difference between the lines is generally not more than 2% of the three-phase average value. Compared with the measured value of the previous part, the change should not exceed 2%, and the neutral point lead wire should not be entangled. The difference should not be more than 1% of the average value of the three-phase. For transformers of 1600kva and below, the difference between the phases is generally not more than 4% of the average of the three-phase, and the difference between the lines is generally not more than 2 of the average of the three-phase. %, the change should not exceed 2% compared with the measured value in the previous part.

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