Isolators in Substation Equipment

These are mechanical switching devices capable of opening or closing a circuit

- While a negligible current is broken or made, or

- Only a small charging current is to be interrupted, or

- When no significant voltage difference exists across the terminals of each pole.

Isolators are capable of carrying current under general conditions and short circuit currents for a specified time. Within open position, the isolator should give an isolating distance among the terminals. The standard value of rated duration of short time current capacity withstands for isolator and earthing switch is generally 1 second. A value of 3 seconds is also sometimes specified. For 33 kV, horizontal type isolating switches are used. The rated normal current is 630 A at 36 kV. For 11 kV, both horizontal and vertical mounting isolating switches of 400 Amps at 12 kV are used.