How to confirm the voltage resistance of 3 kva transformer?

author: FT
10/01/2023

"LI 75 AC 35" means that the lightning impulse withstand voltage of the high-voltage winding lead end of the 10kV transformer is 75kV, and the power frequency withstand voltage is 35kV.
1. The rated withstand voltage of the transformer winding shall be marked with the following letter code:
LI -- lightning shock tolerance voltage
SI -- operating impulse tolerance voltage
AC - power frequency withstand voltage
2. The insulation level of the transformer is indicated by the tolerance voltage value listed in the order of high voltage, medium voltage and low voltage windings (the impact level is in the front), which is separated by diagonal lines.The neutral insulation level plus horizontal line of graded insulation is listed after the insulation level of its wire end.
For example, LI850AC360 -- LI400AC200/LI480AC200 -- LI250AC95/LI75AC35.
Meaning: 220KV three-side graded insulation of the main transformer, the lightning impact withstand voltage of the high-voltage side lead end is 850kV, the power frequency withstand voltage is 360kV, the lightning impact withstand voltage of the high-voltage side neutral point lead end is 400kV, the power frequency withstand voltage is 200kV;
The lightning impulse withstand voltage at the lead end of the middle voltage side is 480kV, the power frequency withstand voltage is 200kV, the lightning impulse withstand voltage at the lead end of the neutral point of the middle voltage side is 250kV, the power frequency withstand voltage is 95kV;The lightning impulse withstand voltage of the low voltage side lead end is 75kV, and the power frequency withstand voltage is 35kva transformer.

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