Protection Relays

Relays or protective equipment are devices that protect power system components and devices from damage and connections by breaking the circuit and opening the power switches.
Before the power switch can be opened, its actuator coil must be turned on. This is done by the relays.
A relay is a device that, following the change of an electrical quantity such as voltage and circulation or a physical quantity such as temperature and oil displacement, causes other devices to work and at the end opens the circuit from the power switch.

Protection relays like :
ABB
Schneider
SIEMENS
GE