Why do transformers have to conduct 5 impact tests before they are put into operation?
The reasons for the impact test before the official investment of the new transformer or the overhaul is as follows:
(1) Check whether the insulation of the transformer and its circuit is weak or defect. When pulling the air load transformer, the operation overvoltage may be generated. When the neutral point of the power system is not grounded or the arc elimination coil is connected to the ground, the voltage amplitude value can reach 4-4.5 times the phase voltage; when the neutral point is directly grounded, the voltage amplitude value can reach 3 times the phase voltage. In order to test whether the transformer's insulation strength can withstand the effect of full voltage or operating overvoltage, before the transformer is put into operation, a short -load full voltage impact test needs to be performed. If the transformer and its circuit have the weakness of the insulation, it will be exposed by the operation over voltage.
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(2) Check whether the transformer differentiation protection is motionless. When the income is input to the air-load transformer, the excitation flow will be generated, and the value can reach 6-8 times the rated current. The attenuation of the excitation surge is faster. Generally, it can be reduced to 0.25-0.5 times the rated current through O.5-1S, but the total attenuation has been completed for a long time. In the early stage of the attenuation of the current, the differential protection was often misunderstood, resulting in the inaccurate transformer could not be invested. Therefore, when the air load is shocking, under the influence of excitation surge, the wiring, characteristics, and fixed values of differential protection protection can be performed, and the evaluation and conclusion of whether the protection can be invested and conclusions can be made.
(3) Assess the mechanical strength of the transformer. Due to the large electric power of the excitation surge, in order to evaluate the mechanical strength of the transformer, a short load impact test is required.
According to the regulations, the number of full voltage air load impact tests, the investment of new products should be impacted 5 times continuously; after large repair, it should be impacted 3 times. Each impact interval is not less than 5min, and someone should be sent to the scene to monitor the transformer before the operation. Check the opposite whether there is any abnormality.
As for why it is set to 5 times is the specific estimation of the specified regulations is the conclusion that the comprehensive consideration of the mechanical strength overvoltage excitation surge flow.
