Electric-Power Substation

an electric power installation or an assembly of electric power equipment used to convert voltages (transformer substation) or current type (converter substation), as well as to distribute electric power to consumers.

The equipment of a substation includes distribution equipment with high-voltage switchgear, the basic converting units, distribution equipment with low-voltage switchgear, and the control board. The distribution equipment with high-voltage switchgear (for voltages up to 1,000 volts [V]) includes switches, circuit breakers, isolators, short-circuit switches, and apparatus for protection against voltage overloads. The basic converting units include transformers, rectifiers, inverters, and frequency converters. Distribution equipment with low-voltage switchgear (for voltages below 1,000 V) includes knife switches, automatic switchgear, and contactors; these are used to switch in or out the distribution lines to consumers. The control board has apparatus for manual or automatic control of the converting units and switchgear; it is also equipped with measuring instruments and apparatus for protection against overloads, short circuits, and excessively low voltage.

In addition, substation equipment includes auxiliary installations and structures, such as storage batteries that supply power to the control systems, repair shops, facilities for inspection of the main units, and installations for reconditioning transformer oil and removing moisture from it. Substations may also be equipped with apparatus for improving the power factor, such as static capacitors or synchronous condensers. Substations that are connected to long, high-voltage power transmission lines are equipped with high-frequency dispatch systems. In such systems, messages are transmitted along the conductors of the power transmission lines.

The equipment can be installed outdoors, or it can be located in a room or in a separate building. In small substations, it can be mounted on wooden, reinforced concrete, or metal poles. Compact, enclosed substations designed to handle 500 kV and higher are envisioned for the future. In these substations, compressed elegaz (sulfur hexafluoride) is used to insulate conductors and buses; it is also used in high-voltage circuit breakers. Such substations are particularly suitable for locations in large cities, where there are no available sites and where conventional high-voltage installations are not permitted.

As a rule, substations are manufactured in plants as complete units. They are delivered to the site either fully assembled or as large modules that are ready for final assembly.