Substations are very important parts of the electrical power systems. The link between the high-voltage transmission lines and the low-voltage power distribution systems is the substation. The function of a distribution substation, such as the one is to receive electrical power from a high-voltage system and convert it to voltage levels suitable for industrial, commercial, or residential use. The equipment used in substations is given below:-


The heart of a power distribution system is an electrical device called a transformer. This device is capable of controlling massive amounts of power for efficient distribution. Transformers are also used for many other applications. It is economically feasible to transmit electrical power over long distances at high voltages since less current is required at high voltages, and therefore line loss (I2R) is reduced significantly. At the substation transformer is used to decrease the voltage at the suitable of safe vale.

Circuit Breakers

Circuit breakers that control high voltages are also located at electrical substations. Circuit breakers can operate under normal or abnormal conditions.


Isolators are used to disconnect electrical equipment from the power lines that supply the equipment. Ordinarily, isolators are not operated when current is flowing through them. A high-voltage arcing problem would occur if isolators were opened while current was flowing through them. They are opened mainly to isolate equipment from power lines for safety purposes.

Lightning Arresters

The purpose of using lightning arresters on power lines is to cause the conduction to ground of excessively high voltages that are caused by lightning strikes or other system problems. Without lightning arresters, power lines and associated equipment could become inoperable when struck by lightning. Arresters are designed to operate rapidly and repeatedly, if necessary.


All power transmission lines must be isolated so as not to become safety hazards. Large strings of insulators are used at substations, and at other points along the power distribution system, to isolate the current carrying conductors from their steel supports or any other ground-mounted equipment. Insulators may be made of porcelain, rubber, or a thermoplastic material. High-voltage insulators are usually made of porcelain.

Protective Relays

Protective relays provide an accurate and sensitive method of protecting electrical equipment from short circuits and other abnormal conditions. Overcurrent relays are used to cause the rapid opening of electrical power lines when the current exceeds a predetermined value. The response time of the relays is very important in protecting the equipment from damage. Some common types of faults that relays protect against are line-to-ground short circuits, line-to-line short circuits, double line-to-ground short circuits, and three-phase line short circuits. Each of these conditions is caused by faulty circuit conditions that draw abnormally high current from the power lines.


Stephen W. Fardo Dale R. Patrick,Electrical Power Systems Technology