Why are transformers subjected to impulse tests?
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Why is an impulse test performed on a newly installed transformer before it is put into operation? How many times is a general impact test conducted, and how is it carried out?
Purpose of transformer impulse testing: to test its insulation and protective devices. Method steps for transformer impulse testing: 1. Perform a full-voltage impulse closing – connect the high-voltage side and disconnect the low-voltage side completely. The power supply should be maintained for no less than 10 minutes, and no abnormalities should be detected upon inspection. 2. The transformer receives power without any abnormalities, with an impulse applied every 5 minutes. Perform 3 to 5 full-voltage impulse closures in succession; the excitation inrush current should not cause the protective devices to malfunction. The final operation should be carried out under no-load conditions. 3. For 110 kV and above neutral-point grounded transformers, the neutral point must be grounded before performing impulse switching. Otherwise, impact closing will cause damage to the transformer.
Isn’t grounding the neutral point a requirement of relay protection when impacting a 110kV transformer? Why does it cause damage to the transformer?