These are used to distribute power to domestic or industrial premises. They may be single-phase or three-phase, pole-mounted or ground-mounted, and they have ratings ranging from 16 kVA up to 2500 kVA. And of transformer type, there are two for choice, one is oil immersed transformer, the other one is dry type transformer.

For oil immersed transformer, the windings and core are immersed in mineral oil, with ONAN cooling. About dry type transformer, the windings are insulated by epoxy resin or NOMEX insulating paper. There are two windings per phase. The primary (high-voltage) winding has a highest voltage ranging from 1.0 kV to 38.5 kV; the secondary (low-voltage) winding voltage does not exceed 1.1 kV. The high-voltage winding is usually provided with off-circuit tappings of ± 2.5 per cent, or +2 × 2.5 per cent, -3 × 2.5 per cent.

Losses are assigned from lists, for instance from BS 7281-1, or by using a loss–capitalization formula.We use amorphous alloy and silicon steel sheet iron core to reduce loss.