The protection system in electrical grid

The protection system in the electrical grid consists of the following components:

1. Current Transformer

2. Voltage Transformer 

3. Protection Relays

4. Circuit Breaker - Trip Coil

5. Equipment (Generator, Transformer, Line, or Medium Voltage Cell)

6. DC supply for the protection devices, circuit breaker operation, and isolators

7. Communication system between stations, either PLC or fiber optic cables

8. Bus

9. Protection device control system, which allows for changing the protection device settings or retrieving fault records. This can be done either directly at the protection device through the HMI (Human-Machine Interface) or remotely through a control center in a substation automation system (SAS).

This is a comprehensive overview of the protection scheme, but there are some variations. For example, in transformer protection, there is no voltage transformer connected to the protection device, and there is no communication system, as this system uses the distance relay to accelerate the tripping.  

There can also be more than one protection device on a transformer or a circuit, and there may be two trip coils.