Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations cowski on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
using 2 taps on a multi-ratio CT 3
- Thread starter BrkfldEE
- Start date
Dear Mr BrkfldEE (Electrical)(OP)29 Mar 21 15:31
B. " Will using 2 different taps of a multi-ratio CT work? Will it cause any problems? "
C. I may have mistaken your question. I try to answer as following. e.g. a CT with 200/1 and 100/1 toppings.
1. With present load is < 100A,
a) use 100/1 tapping for any load, depending on the CT Class,
b) at the same time, the 200/1 tap may also be be used for any load, depending on the CT Class; without any problem,
c) when the 200/1 tap is not in use, it SHALL be shorted.
2. With future load >100A but <200A,
a) use 200/1 tapping for any load, depending on the CT Class,
b) the 100/1 tap is not used for any load,
c) when the 100/1 is not in us, it SHALL be shorted.
Che Kuan Yau (Singapore)
-
1
- #4
davidbeach
Electrical
Wrong.
I’ll see your silver lining and raise you two black clouds. - Protection Operations
I’ll see your silver lining and raise you two black clouds. - Protection Operations
-
1
- #5
- Thread starter
- #6
thermionic1
Electrical
Is this an ANSI MR CT (bushing or donut) or an IEC HV Type CT?
LionelHutz
Electrical
You asked 2 questions. Will it work? Will it cause problems? The answers are no and yes.
- Thread starter
- #9
thermionic1
Electrical
"So I am hearing that using 2 taps on a CT at the same time will NOT work correctly"- You are hearing correctly. Don't do that, it wont work.
You can run multiple relays in series with a CT on a single tap (ex X1-X2 or X1-X5). Multiple relays in series may work out, depending on the settings used and if it's a digital relay. If you put a diff relay in series with something else, put the diff first. It's possible that someone using a Doble with an FT paddle can inadvertently short out the diff relay, if the test paddle is plugged into the Doble first and short out the diff relay (possibly causing a trip), if the relay is in service.
You can run multiple relays in series with a CT on a single tap (ex X1-X2 or X1-X5). Multiple relays in series may work out, depending on the settings used and if it's a digital relay. If you put a diff relay in series with something else, put the diff first. It's possible that someone using a Doble with an FT paddle can inadvertently short out the diff relay, if the test paddle is plugged into the Doble first and short out the diff relay (possibly causing a trip), if the relay is in service.
oldfieldguy
Electrical
You WILL have two conductors connected to the CT. This is NOT the same as using two taps. You choose the two taps that give you the ratio suitable for your application. All other taps are left floating.
old field guy
old field guy
electricpete
Electrical
I'm not an expert on field wiring of CT's, but it seems to be if I have 5 taps let's say X1,X2,X3,X4,X5 then the every winding segment between taps should be included in one (and only one) external circuit loop or short. (Segment X1-X2 needs to be included in one and only one external circuit or short; Segment X2-X3 needs to be included in one and only one external circuit or short; etc).
Applying this rule:
If I feed an external circuit loop by connecting to X1 and X3, then I need to short from X3 to X5 so that no segment of the CT is open-circuited.
If you need to add more devices typically they would all be in series in that one external circuit X1-X3. In theory if the burden is getting too high on that circuit I guess you could feed another external circuit from X3 to X5 assuming your calculate the ratio correctly. You could not add another external circuit connected between X1 and X4 because then the segments X1-X2 and X2-X3 would be shared among multiple external circuits.
That's my take, I apologize if I'm repeating what others more knowledgeable than me have said. If I said something wrong please feel free to correct me, then I'd learn something.
=====================================
(2B)+(2B)' ?
Applying this rule:
If I feed an external circuit loop by connecting to X1 and X3, then I need to short from X3 to X5 so that no segment of the CT is open-circuited.
If you need to add more devices typically they would all be in series in that one external circuit X1-X3. In theory if the burden is getting too high on that circuit I guess you could feed another external circuit from X3 to X5 assuming your calculate the ratio correctly. You could not add another external circuit connected between X1 and X4 because then the segments X1-X2 and X2-X3 would be shared among multiple external circuits.
That's my take, I apologize if I'm repeating what others more knowledgeable than me have said. If I said something wrong please feel free to correct me, then I'd learn something.
=====================================
(2B)+(2B)' ?
-
1
- #14
davidbeach
Electrical
Nope, two wires as stated by oldfieldguy. Even that means the two wires are connected to X2 and X3 with X1 and X4 & X5 floating. The taps work by because all of the amp*turns of the secondary occur between those two connection points. Fewer turns means more amps. If there are other possibilities for amp*turns on the secondary none of the currents will have the correct ratio and the actual ratios will be determined by how the burdens relate.
I’ll see your silver lining and raise you two black clouds. - Protection Operations
I’ll see your silver lining and raise you two black clouds. - Protection Operations
electricpete
Electrical
ok thanks David. You're right, I wasn't thinking about it correctly, wasn't thinking about the amp-turns balancing as the key aspect. It makes sense now that I think about it that way. (I think I knew that once upon a time but I got a little rusty somewhere along the way).
=====================================
(2B)+(2B)' ?
=====================================
(2B)+(2B)' ?
- Status
Similar threads
- Locked
- Question
- Question
- Locked
- Question