Transformer ratio measurement
Generally judging the quality of a transformer requires the following tests: AC withstand voltage, DC resistance, transformation ratio, capacity, and no-load loss.
For the transformation ratio test, it is mainly to measure the actual transformer transformation ratio error. The nameplate on the transformer has a voltage indicating the tap position of the high-voltage side. The low-voltage side is also marked with 0.4kV or 400V, and the high-voltage side voltage divided by 400 is the rated transformation ratio of this gear. What needs to be measured is the error between the actual measured transformation ratio and this rated transformation ratio.
Transformer ratio error
1. The transformation ratio is a concept of calculation error in transformer design. Generally, when the transformation ratio is greater than 3, the transformer transformation ratio error needs to be less than 0.5%; when the transformation ratio is less than or equal to 3, the transformer transformation ratio error needs to be less than 1%.
2. The induced potential in the primary winding of the transformer and the secondary winding of the transformer is proportional to the number of turns of the winding. According to the same power on both sides, the power is equal to the ratio of the square of the voltage to the resistance, which results in the voltage ratio, that is, the transformation ratio.
3. The ratio of the input voltage of the primary winding to the output voltage of the secondary winding is equal to their turns ratio, and the ratio K is called the ratio coefficient. Example: The transformation ratio of the transformer is 110kV/11kV=10.
Analyze the cause of transformer ratio error
1. There is an error in the number of turns during the winding of the transformer;
2. The magnetic flux generated by the primary coil of the transformer cannot pass through the secondary completely, and there is a phenomenon of "magnetic leakage";
3. There is a voltage drop on the working current of the transformer, including DC resistance and leakage inductance.
Qualified range of transformer ratio error
Below 35kV, if the voltage ratio is less than 3, the allowable deviation of transformer voltage ratio is plus or minus 1%. The allowable deviation of voltage ratio of all other transformers is plus or minus 0.5%.