Distribution transformer

Since distribution transformers are energized 24 hours a day (even when they don't carry any load), reducing iron losses is vital in their design.

They are often used for the power supply of facilities outside settlements, such as isolated houses, farmyards, or pumping stations at voltages below 30 kV.

In urban areas and neighborhoods where primary distribution lines run underground, padmount transformers, and locked metal enclosures are mounted on a concrete pad.

An electrical fault melts the fuse, and the device drops open to give a visual indication of trouble.

In some cases, completely self-protected transformers are used, which have a circuit breaker built in, so a fused cutout isn't needed.

[8][9] Where large numbers of transformers are made to standard designs, a wound C-shaped core is economical to manufacture.

A steel strip is wrapped around a former, pressed into shape, and then cut into two C-shaped halves re-assembled on the copper windings.

The entire assembly is baked to cure the resin and then submerged in a powder-coated steel tank, which is then filled with transformer oil (or other insulating liquid), which is inert and non-conductive.

The tank is temporarily evacuated during manufacture to remove any remaining moisture that would cause arcing and is sealed against the weather with a gasket at the top.

[citation needed] Formerly, distribution transformers for indoor use would be filled with a polychlorinated biphenyl (PCB) liquid.

[citation needed] Pad-mounted transformers have secure locked, bolted' and grounded metal enclosures to discourage unauthorized access to live internal parts.

The enclosure may also include fuses, isolating switches, load-break bushings, and other accessories as described in technical standards.

[citation needed] In the United States, distribution transformers are often installed outdoors on wooden poles.

Single-phase distribution transformer in Canada
Two three-phase transformers in Hungary
Railroad signal power supply transformer (CP-SLOPE interlocking ) in west of Altoona with a warning label indicating that it contains PCBs .
Phase-to-phase transformer in Britain
Primary line on the right toward the front and secondary lines in the back of this single-phase transformer
A "transformer bank", widely used in North America: three single-phase transformers connected to make a 3-phase transformer.
Oil-cooled three-phase distribution transformer, similar to one in above photo, with housing off, showing construction.
Distribution substations inside a small tower-like building are common in Europe. Near Jelenia Góra , Poland