Connecting two zero sequence CT in parallel

[Besoeker]

CB1 (source breaker) is existing facility and out of our project scope!

Then are you allowed to apply a tripping circuit to it?

 

[Phil Corso]

Mousa...


Second relay will aid in quickly determining which of the two circuits is faulted!

Regards, Phil Corso

 

[Besoeker]

Mousa...


Second relay will aid in quickly determining which of the two circuits is faulted!

Regards, Phil Corso

And allow the other supply to keep on supplying.

 

[Ingenieur]

And allow the other supply to keep on supplying.

he would have to move the ct to the load side of cb a and b
leaving them on the 1 to a/b feeder would be an option, but not a good one
and still not protect the 1 to a/b feeder

so if the fault was beteeen 1 and a or b it would go undetected
he wants to protect the feed from 1 to a/b

 

[Besoeker]

he would have to move the ct to the load side of cb a and b
leaving them on the 1 to a/b feeder would be an option, but not a good one
and still not protect the 1 to a/b feeder

so if the fault was beteeen 1 and a or b it would go undetected
he wants to protect the feed from 1 to a/b

Yes, obviously they would have to fitted on the load side of a and b.
But, in my opinion, that would be a better option. Especially if they are not yet installed.

 

[Ingenieur]

Yes, obviously they would have to fitted on the load side of a and b.
But, in my opinion, that would be a better option. Especially if they are not yet installed.

that would not protect the 1 to a/b feeder which appears to be his intent

his question: can he parallel the 0 seq ct's to drive 1 relay to trip cb1?
yes
perfectly acceptable, std practice, as noted in the white paper

 

[Besoeker]

that would not protect the 1 to a/b feeder which appears to be his intent

Do you have such a thing as fault free zones?

 

[Ingenieur]

Do you have such a thing as fault free zones?

but it is good practice to cover long feeders
and keep the length between ct and cb as short as practical

 

[Besoeker]

but it is good practice to cover long feeders
and keep the length between ct and cb as short as practical

Agreed. Do you how far CBa and CBb are from CB1?

 

[mbrooke]

imo use 2 relays or another ct (summed 1 per phase)

This :happyyes: Or a single relay that produces operate and restraint values summing internally. CT saturation can produce unwanted tripping.

 

[Mousa]

Then are you allowed to apply a tripping circuit to it?

yes it is allowed to trip CB1

actually each of CB a and CB b have there ZCT, the issue about the CT which will trip CB1

 

[Mousa]

he would have to move the ct to the load side of cb a and b
leaving them on the 1 to a/b feeder would be an option, but not a good one
and still not protect the 1 to a/b feeder

so if the fault was beteeen 1 and a or b it would go undetected
he wants to protect the feed from 1 to a/b

CB A and CB B have there ZCT for gf protection, the issue about the CT which will trip CB1
All of this CTs to protect both sides (source and load breakers) from fg in the cable connection between them, the cables long around 150 m

 

[Mousa]

that would not protect the 1 to a/b feeder which appears to be his intent

his question: can he parallel the 0 seq ct's to drive 1 relay to trip cb1?
yes
perfectly acceptable, std practice, as noted in the white paper

yes, the goal to protect CB1, CBs a and b already protected by there ZTCs and relays
thank you dear

 

[Wyo721]

CT's typically are not sequenced

CT's typically are not sequenced

What is the CT ratio? The burden on the relay? if one trips it takes out the entire system correct? What is the trip setting range on the relay? Which breaker does it trip? Lots of thoughts but mostly just questions? Who specs the equipment and designed the system?