Capacitors consume active power and release reactive power. They also present a low impedance to harmonics in other words they attract harmonic frequencies. Thus, capacitor banks are installed in substations to:
Insulators make sure the energized parts do not touch the ground. All substation equipment in contact with an energized line or bus employs an insulator.
Relays need to know the current magnitude – either for metering or protection. A current transformer (CT) fulfills this role, stepping down thousands of amps to (typically) 5A which is then fed to a relay.
Relays need to know the voltage magnitude – either for metering or protection. A voltage transformer fulfills this role – it steps down thousands of volts to 67V/115V in high voltage stations (at the medium voltage the VT’s step it down to 120V) which is then fed to a relay.
A circuit switcher is a switching device like a circuit breaker. It interrupts the power flow.
It is typically installed on the high voltage side of the transformer.
