Evaluation between earth switch and earth truck for 11kV Switchgear

[krisys]

Can anyone throw some light on the evaluation between earth switch and earth truck for 11kV Switchgear.

I personally feel that earth switch is better, as it is integral part of the switchgear, less prone to deterioration due to external factors, storage is not a problem etc.
Less chance to commit mistake and safer compared to earth truck.

 

[waross]

I am not familiar with the term "earth truck".

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Bill, something like this. I've also seen versions which don't include the switch, they simply rack in to the board in place of the breaker.

krisys,

In my opinion a fault-making earth switch built into the gear, or a transfer earth applied through a withdrawable circuit breaker, would be preferable to an earth truck.

 

[waross]

Thanks Scotty.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[crshears]

"Earth truck" sounds like what my utility calls a "ground and test device," made to take the place of a circuit breaker within a switchgear cubicle. One design of GTD I've seen has two sets of insulated contacts similar to what Scotty is describing, viz., one each for the supply and load sides, brought out to a horizontally divided box with a lockable hinged lid; the two faces of the lid bear the words "BUS" and "FEEDER," allowing the GTD to be guaranteed locked in such a way as to permit access to only the intended side.

A major disadvantage of going the GTD route is when more than one feeder requires grounding simultaneously, specifically in a dense urban setting with all underground cables and no overhead conductor at all, something I've seen happen numerous times. For this reason I'd go with "earthing switches" instead, particularly in the case described.

CR

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

 

[ScottyUK]

If you accidentally manage to close an earth switch onto live conductors it should withstand the fault long enough for protection to clear it. If you accidentally insert an earthing truck into the wrong holes it will very probably be Game Over.

Fault-rated earth switches or a circuit breaker transfer earth are much safer ways to apply an earth.

 

[crshears]

Our GTDs normally have no intrinsic connection to ground, but I can see how the type Scotty described could have and could therefore inadvertently or, more likely negligently, be racked onto live equipment. In that case, hope the switching agent is wearing a good bomb suit, as I wouldn't want to be counting on the arc rating of the enclosure.

CR

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