Read the text. Distribution Transformers

Distribution Transformers

Besides conductors and insulators, many other pieces of equipment are necessary to get electric power from the generator to a consumer. The distribution transformer is certainly the most important of these pieces of equipment. Without the distribution transformer, it would be impossible to distribute power over such long distances. The purpose of a transformer is to step up or step down voltage. In the case of the distribution transformer, the voltage is stepped down from that of the primary mains of a distribution circuit to that of the secondary mains. In most cases, this is from 2400, 4160, or 13,800 volts to 120 or 240 volts.

Most distribution transformers consist of (1) a closed-loop magnetic core on which are wound two or more separate copper coils, (2) a tank in which the corecoil assembly is immersed in cooling and insulating oil, (3) bushings for bringing the incoming and outgoing leads through the tank or cover.

Bushings

A bushing is an insulating lining for the hole in the transformer tank through which the conductor must pass. Primary bushings are always much larger because the voltage is higher at that point. Sometimes the primary and secondary bushings are called high-voltage and low voltage bushings.

Distribution transformers are almost always located outdoors where they are hung from crossarms, mounted on poles directly.

How a transformer is mounted is a matter of considerable importance. The distribution transformer must stay put and continue functioning even in the midst of violent winds, pouring rain, freezing cold, sleet, and snow. Besides weather, there is danger of the pole itself being hit by a carelessly driven vehicle.

Modern pole-mounted transformers have two lugs welded directly on the case. These lugs engage two bolts on the pole from which the whole apparatus hangs securely. This method, which is known as direct mounting eliminates the need for crossarms and hanger irons thus saving a considerable amount of material and labor.

A transformer should not be mounted on a junction pole (a pole supporting lines from three or more directions) as this makes working on such a pole more hazardous for the worker.

Manufacturers produce two types of distribution transformers: the conventional and the completely self-protected. (CSP)

A conventional distribution transformer consists only of a case containing the transformer unit with protective devices, usually a primary fuse cutout and a lightning arrester, mounted separately on the pole or crossarm.