The purpose of testing the impact of closing the transformer into operation before

The purpose of the impact of closing the transformer has two tests:
When opened load transformer, it is possible to produce over-voltage operation. When ungrounded or Petersen coil grounded neutral point in the power system, over-voltage amplitude up to 4 to 4.5 times the phase voltage; directly grounded neutral point, up to 3 times the phase voltage. In order to check the dielectric strength of the transformer can withstand full operating voltage or over-voltage, impact testing to be done.  electric meter  into no-load transformer inrush current is generated, the value of up to 6-8 times the rated current. The inrush current begins to decay rapidly, generally over 0.5 seconds is reduced to 0.25 to 1 to 0.5 times the rated current value, all in a longer decay time, up to large-capacity transformers tens. Due to a large  Voltage stabilizer  generated electric power, in order to assess the mechanical strength of the transformer, while the initial assessment of the inrush current decay protection devices can cause malfunction, need to do the impact test.