Every neutral terminal of the transformer shall be marked with the letter corresponding to the winding and followed by the number zero. The bushings must comply with standards NBR 5034, NBR 5435 and NBR 5437 and must be approved suppliers for the supply of porcelain insulators.
Transformers with rated voltage of 13.8 kV and 23.1 kV must be supplied with 150 kV NBI bushings with a minimum flow distance of 450 mm. Transformers with nominal voltage of 34.5 kV shall be supplied with NBI bushings 170 kV and with a minimum runoff distance of 680 mm. BG11-1-5-5
The cover shall be provided with rebates for mounting the high voltage bushings. The connection terminals of single-phase and three-phase transformers must be of types T1, T2 or T3, according to ABNT NBR 5437. For transformers smaller than 112.5 kVA, the low voltage bushing must comply with the T1 standard of the NBR 5437.
For transformers with power greater than or equal to 112.5 kVA, the low voltage bushing must be standard 2 or 4 holes according to standard T2 and T3 of NBR 5437.