The reasons for the impact test of the new transformer or the overhauled transformer before it is put into operation are as follows:
(1) Check whether there are weaknesses or defects in the insulation of the transformer and its circuit. When the no-load transformer is pulled open, it is possible to generate operating overvoltage. When the neutral point of the power system is not grounded or grounded through the arc suppression coil, the overvoltage amplitude can reach 4-4.5 times the phase voltage; when the neutral point is directly grounded, the overvoltage amplitude can reach 3 times the phase voltage. In order to test whether the insulation strength of the transformer can withstand the full voltage or operating overvoltage, it is necessary to do no-load full voltage impulse test before the transformer is put into operation. If the transformer and its circuit have insulation weaknesses, it will be exposed by operating overvoltage breakdown.
(2) Check whether the transformer differential protection is malfunctioning. When no-load transformer is charged, the inrush current will be generated, and its value can reach 6-8 times the rated current. The magnetizing inrush current starts to decay faster, generally it can be reduced to 0.25-0.5 times the rated current after 0.5-1s, but all attenuation takes a long time, about a few seconds for small and medium-sized transformers and 10-20s for large transformers. Therefore, at the initial stage of magnetizing inrush current attenuation, differential protection is often misoperated, resulting in transformer failure to be put into operation. Therefore, when no-load impact closing, under the action of excitation inrush current, the wiring, characteristics and fixed value of differential protection can be actually checked, and the evaluation and conclusion of whether the protection can be put into operation can be made.
(3) assessment of the mechanical strength of the transformer. Because the inrush current produces a lot of electric power, in order to assess the mechanical strength of the transformer, it is necessary to do no-load impact test.
After the first impact, it should continue to run for more than 10 minutes, and after the impact, it should wait for more than 5 minutes before the next impact. As for why it is set to 5 times is stipulated in the regulations, the specific estimation is the conclusion drawn from the comprehensive consideration of mechanical strength, overvoltage and inrush current.
Above is introduction of Ankejie Testing Certification to Transformer Impact Test, for reference only, some of the material comes from the Internet and does not represent the point of view of Ancor's detection technology and is responsible for its authenticity. If you are involved in the content of the work, copyright and other issues, please contact us within 30 days, we will delete the content in the first time!
