Isolation current transformer
Isolation current transformer
(OP)
Why we need to have an isolation current transformer for metering if we using the 600/300/5A, class 5P20, 15VA ring type current transformer for overcurrent and earthfault protection?






RE: Isolation current transformer
In 5P20 CT the limits of the current error at rated primary current will be +/- 1%, the phase angle error at rated primary current will be +/- 60 minutes and the composite error will be +/- 5%. This shows there is a very high tolerable value for protection CT. Of course Class 5 accuracy is also available in measuring CT. But generally for measuring CT class 1 or better is used. So the cores will be different for measuring CT and the protection CT. For protection you may even need two separate cores because of different use of the protective relays.
RE: Isolation current transformer
RE: Isolation current transformer