The voltage ratio of the transformer (referred to as the transformation ratio) is the ratio of the high-voltage winding voltage U1 to the low-voltage winding voltage U2 when the transformer is no-load, that is, the transformation ratio k=U1/U2. The transformation ratio test of the transformer is a test to verify whether the transformer can achieve the specified voltage conversion effect and whether the transformation ratio test meets the transformer conditions or the value specified on the nameplate. The purpose is to check whether the number of turns of each winding, the assembly of lead wires, and the indication position of the tap changer meet the requirements; and to provide the basis for whether the transformer can operate in parallel with other transformers. The parallel operation of small and medium-sized transformers with a ratio difference of 1% will generate a circulating current of 10% of the rated current in the transformer windings, and the loss of the test transformer will increase greatly, which is not good for the transformer.
In the process of power transformer production, user handover and maintenance test, the transformer ratio test is a must-do item, which can effectively supervise the quality of the transformer products during delivery and use, and prevent the transformer from short circuit, open circuit, connection error, and voltage regulation. Internal switch fault or contact fault.
Automatic ratio tester test standard:
The reference standard of the automatic ratio tester is DHT963-2005. The "Regulations" stipulate the standards for the ratio test of all taps of transformer windings:
1. Compared with the nameplate value, the transformation ratio of each corresponding tap should not be significantly different, and should comply with the law.
2. For transformers with a voltage below 35kv and a transformation ratio of less than 3, the allowable deviation of the transformation ratio is 1%, and the allowable deviation of the rated tap transformation ratio of all other transformers is 0.5%. The transformation ratio of other taps should be in the percentage value of the transformer impedance voltage less than 1/10, but not more than 1%.
Transformer ratio measurement should be carried out at all tap positions. For on-load voltage regulating transformers, electric devices should be used to adjust the tap position. For three-winding transformers, only the changes of two pairs of windings need to be measured. Generally, the changes between a winding with a tap changer and the other two windings are measured. For windings with a tap changer, the transformation ratio at all tap positions should be measured.