Three Position Switch in GIS

[tszpun]

Hello Experts,
Could somebody explain what is the advantagr of using three position switch in the GIS? Can't it be done by Circuit breaker + earthing switch? Or why we can't use just two position switch (no middle position)
Thanks,

 

[sushilksk]

Are you talking about three positions:
[ol 1]
[li]Disconnector close, Earth switch open[/li]
[li]Disconnector open, Earth switch open[/li]
[li]Disconnector open, Earth switch close[/li]
[/ol]

It has advantage of having only one drive mechanism for both disconnector and earth switch.

 

[crshears]

My utility insists on having a visibly open isolation point for when work protection is being established, and as very few breaker contacts can be visibly confirmed open, breaker plus earthing switch simply wouldn't fly.

True enough, only one drive mechanism for two devices, but at the cost of operational flexibility; we have had ground switches become inoperative in the open position, and having the ability to establish an open point further out and ground through a guaranteed closed switch has gotten us out of many a jam [ I've written about this before ].

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]