Why relays are used in Power System?

The electrical power system deals with the generation, transmission, and distribution of various voltage levels and it works on a very big network. So proper precautionary levels must be adopted to prevent accidents and save both human and costly appliances. Basically, the expense related to the power system (installing, maintenance, etc.) is quite high. So this also increases the need of taking adequate safety measures.

Various measures are taken to increase the safety of a power system network. Because a huge flow of current in any circuit can damage the costly equipment connected with it. Relay and circuit breaker combination is the most widely used protective measure. The main operation of relay is to sense the excess flow of current and trip the circuit breaker coil which disconnects the faulty part of the network from the healthy part so that the huge current flow does not affect the equipment of that healthy area. The relays not only trip the circuit breaker when huge current flows through the system but also they are used to detect the various abnormal condition of the system by alarming. There is some special type of relays which are called non-trip relay as they are only used for alarming purposes. In addition to that there are some tripping relays that are not actuated by the overcurrent in the system, but by over-voltage, under-voltage, over frequency, under frequency, as these are also abnormal conditions of the system. Also, there are various mechanical relays used in the electrical power system, which are actuated by the thrust of insulating oil (Buchholz Relay in power transformer), SF6gas pressure (density monitor in SF6 circuit breaker), or air pressure (in pneumatic circuit breaker)etc. But whatever may be the type of relays, each of them is installed in electrical power system to prevent abnormalities in the system.