Influence of different ratios of main transformers on the operation of generator sets

Large-capacity transformers with different ratios running in parallel on the same 220KV system bus line have the following effects on each generator set:

1 The reactive power of each generator set in each generator-transformer group operating in parallel is not balanced and reasonably distributed. Under the same 220KV system bus voltage, the corresponding generator terminal voltage of the transformer is always low, which is not up to the rated value. In order to meet the rated voltage requirement, the excitation regulator of the generator automatically increases the excitation of the generator. So that the generator needs to be connected with a large reactive load to basically maintain its terminal voltage, so that its corresponding generator stator and rotor currents are too large, the operating temperature of the various parts of the unit and the excitation system equipment is high, and the heat is generated. The loss is increased; and the transformer with smaller transformer is always higher than the corresponding generator terminal voltage under the same 220KV system bus voltage, the generator reactive output is small, which makes the reactive load distribution of each unit unreasonable. Not conducive to safety and economic operation;

2 The transformer system of the corresponding generator set of the transformer with large ratio is too low. The 6KV bus voltage is always low (sometimes not reaching the rated value), which is unfavorable to the normal operation of the plant system equipment, which not only increases the loss of the plant power. And relatively reduce the efficiency of the generator;

3 pairs of 220KV system voltage regulation requirements are not easy to meet. Under the same 220KV system bus voltage, due to the large error of the transformer's transformation ratio, some generator outlet voltage has exceeded the rated voltage, and its excitation regulator will automatically reduce the excitation output of the generator, thereby reducing the generator outlet voltage; In some generators, the outlet voltage has not reached the rated voltage, and the excitation regulator will automatically increase the excitation output of the generator, thereby increasing the generator outlet voltage. The regulation of the system voltage is opposite, forming a contradiction and causing a vicious circle. Does not meet the requirements of system voltage adjustment.

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