General method for insulator piece count:

At an altitude of 1000 meters below the trailer: 35 kv four slices of 7, 220, 110, 13, 330, 17 pieces of 25, 500.

Tension of the corresponding + 1 piece, 500 kv + 2 slices.

At an altitude of 1000 meters above according to the formula N = N (1 + 0.1 (H - 1)) to calculate.

N - the number of insulator below 1000 metres.

H - altitude.