CTs in Switchgears
CTs in Switchgears
(OP)
Dear sirs
Most of american switchgears has as standard one CT per phase (Total:3) in order to use it for protective and measurement, while most of european switchgears have 02 CTs per phase (total:6)for the same use (protective &measurement). ¿What is the technical advantage to use one one CT per phase? ¿Is there any American standard that explain something about this subject?
Thanks
Most of american switchgears has as standard one CT per phase (Total:3) in order to use it for protective and measurement, while most of european switchgears have 02 CTs per phase (total:6)for the same use (protective &measurement). ¿What is the technical advantage to use one one CT per phase? ¿Is there any American standard that explain something about this subject?
Thanks






RE: CTs in Switchgears
A lot of switchgear only has one set of CTs because that is less expensive. With modern digital relaying and monitoring equipment, the CT burden is so low that one set of CTs is perfectly adequate. In the old days, with electro-mechanical devices, there was an advantage in using a separate set of CTs for relaying and another set for metering.
It is still difficult to obtain high metering accuracy in the toroidal CTs typically used on switchgear breakers.
RE: CTs in Switchgears
I don't believe that's a very accurate statement regarding ANSI medium-voltage metalclad assemblies. The North American IEEE C37{.20}-series switchgear standards do not seem to support the assertion.
Stock {unmodified} insulated throats as part of primary disconnects {six per drawout beaker} readily permit two 600V-class CTs each, allowing 4 per phase and 12 per breaker cell. In any case, I am not sure what purpose providing more CTs than needed for the application at hand would serve.
RE: CTs in Switchgears
RE: CTs in Switchgears
RE: CTs in Switchgears
It is common American practice to use one set of (relaying accuracy) CTs for both metering and relaying. I have never heard of a meter being damaged by fault current with this arrangement. The accuracy is not revenue class, but in most cases, this level of accuracy is not needed.
RE: CTs in Switchgears
there are cts that have both relaying and metering class (e.g., C100, 0.3B1.8 or IEC rated 30va 5P20 protection class and 15 va CL0.5 metering class). some are approved for revenue metering.
with today's electronic relays and meters having low burdens, high relaying accuracy/burden are not that required.
RE: CTs in Switchgears
RE: CTs in Switchgears