For  long-distance  transmission,  a  voltage  higher than  normally generated  is  required.  A  step-up transformer is used to produce the high voltage. Most electrical equipment in the Navy uses 120/208 volts. The  primary  voltage  distributed  on  Navy  shore installations, however, is usually 2,400/4,160 and 13,800 volts.

A distribution transformer (step-down) is required to reduce the high-primary voltage to the utilization voltage of 120/208 volts. The various types of transformer installations are discussed later in this chapter.  Regardless  of  the  type  of  installation  or arrangement, transformers must be protected by fused cutouts or circuit breakers; and lightning arresters should be installed between the high-voltage line and the fused cutouts.

Three  general  types  of  single-phase  distribution transformers are in use today. The conventional type requires a lightning arrester and fuse cutout on the primary-phase conductor feeding the transformer. The self-protected  (SP)  type  has  a  built-in  lightning protector;  the  completely  self-protected  (CSP)  type has the lightning arrester and current-overload devices connected to the transformer and requires no separate protective devices.

In  primary  and  secondary  windings  construction, the change in voltage in a transformer depends on the number of turns of wire in the coils. The high-voltage winding is composed of many turns of relatively small wire, insulated to withstand the voltage applied to the winding. The secondary winding is composed of a few turns of heavy copper wire, large enough to carry high current at a low voltage.