Working Princilple of 132/33KV PGCB Grid Substation's equipments. What is a GRID and how it works? 

PGCB 132/33 KV grid substations working principle. What's the equipments of a grid sub-station? How they works? what is the purpose of a grid substation?
Separate videos on bellow listed equipments:
1.String Isolator Video up comming.
2. (lightning Arrestor) video up comming.
3. CVT (capacity voltage transformer) video upcoming.
4. CT (Current Tansfomer) Video Up comming.
5. Instrument Transformer video up comming
6. DS (Disconnecting Switch) video upcomming.
7. SF6 circuit Breaker video up comming.
8. Bus Conductor video up comming.
9. SLD (Single line Diagram) video Up comming.
10. Power Transformer video • Basic Parts of 33/11kv...
• What is the Working Pr...
11. 33KV Switching Station video Up comming.
12. Transformer protection video up comming.