CT missing on 15kV incoming feeder to a disconnect switch

D

Dale001289

Senior Member
Location
Georgia
We have a 15kV disconnect switch being added to an existing system. The new 15kV cable will be tapped off the line side of an existing switch located upstream. The one line diagram does not show a CT where the cable terminates at the new disconnect switch.
I’m used to seeing a zero-sequence CT on the incoming cable to MV switchgear at the MCB….not sure how the system will see a ground fault without it.
What am I missing here?
 
Dale001289 said:
I’m used to seeing a zero-sequence CT on the incoming cable to MV switchgear at the MCB….not sure how the system will see a ground fault without it.
What am I missing here?
Click to expand...
It is possible there is a protective relay is using a GF function that sums the individual CTs.
 
There might be…but incredibly, it’s not shown on the one line. (I suppose I’ll have to ask engineering)
You do agree there should be some sort of protection on the incoming 15kV right?
 
Dale001289 said:
There might be…but incredibly, it’s not shown on the one line. (I suppose I’ll have to ask engineering)
You do agree there should be some sort of protection on the incoming 15kV right?
Click to expand...
Is there a breaker upstream of the tap point? It would be able to provide the GF function. Is your system grounded?

Are you adding a fusible switch or a breaker with a protective relay?
I have seen many fusible switches, without GF, feeding transformers and motor starters.
 
jim dungar said:
Is there a breaker upstream of the tap point? It would be able to provide the GF function. Is your system grounded?

Are you adding a fusible switch or a breaker with a protective relay?
I have seen many fusible switches, without GF, feeding transformers and motor starters.
Click to expand...
Yes there is a vacuum CB upstream- the XFMR is delta delta ungrounded and the new disconnect switch is fused which is on the primary side of the Transformer.
For what you’re saying it sounds like things might be ok from a protection standpoint
 
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