CT Ratio Test
CT Ratio Test
(OP)
I have just worked a job site where the requirement was to ratio test the CT's at a number of test currents (400:5 A CT, tested at 100, 200, 300, and 400 A primary current).
I am familiar with testing CT's for ratio for different taps, but only 1 point per tap.
Does anyone know of this practice and what the value is of testing at numerous currents?
Thanks
Ken
I am familiar with testing CT's for ratio for different taps, but only 1 point per tap.
Does anyone know of this practice and what the value is of testing at numerous currents?
Thanks
Ken






RE: CT Ratio Test
Are these CTs being used for protection or metering?
RE: CT Ratio Test
Thanks for your response.
Ken
RE: CT Ratio Test
Would 100, 200, 300, and 400 Ampere-Turns meet the spec?
No offense meant to anyone, but if no particular secondary burden is called out, it sounds like a waste of time.
RE: CT Ratio Test
Most of the O/E think that by making the contractor mobilize a BIG injection kit the contractor's money is correctly spent! I have done from 100A injection for 3000/1A CT (just one point, with acceptance criteria being the secondary current nearly meeting the specified ratio) to 10%, 50% and 100%or1000A whichever smaller to a mixed setup with 600-400/1A and 3000-2500/1A CTs!
Technically speaking, the Magnetization current test and the Rct test complementing the ratio CHECK test at 10%(and not accuracy test) certify the correctness of the CT delivered to site. Burden measurement / loop resistance measurement during the CT circuit check test and ofcourse the polarity tests complete all that is required to certify Current Circuit correctness. But then who has time to convince the stubborn reps of reputed O/Es?!
I have also done magnetization current test on METERING cores to prove that the cores are indeed metering cores!
Best regards