CT accuracy class for Transformer differential protection per IEEE
CT accuracy class for Transformer differential protection per IEEE
(OP)
I have few queries regarding CT accuracy class selection for Transformer differential protection as per IEEE C37.110-1996.
IEEE C37.110's worked example indicates that only one way CT lead(cable)resistance shall be considered for total burden calculation. Where as IEC/European standards require the return path resistance also to be included for 'knee point voltage' calculation (Vk=2*If*(Rct+2Rc). Could any one please clarify how oneway resistance will be enough to calculate the 'C' voltage rating to minimize the CT saturation.
Further, the indicated burden value in the worked example calculation for C200,4.16KV CT is just 1/4th (0.5 ohm) of the standard CT burden (2 ohm,B-2 burden) as given in Table 9, IEEE C57.13. Will the actual value be normally 1/4 th of standard value for all CTs..?
IEEE C37.110's worked example indicates that only one way CT lead(cable)resistance shall be considered for total burden calculation. Where as IEC/European standards require the return path resistance also to be included for 'knee point voltage' calculation (Vk=2*If*(Rct+2Rc). Could any one please clarify how oneway resistance will be enough to calculate the 'C' voltage rating to minimize the CT saturation.
Further, the indicated burden value in the worked example calculation for C200,4.16KV CT is just 1/4th (0.5 ohm) of the standard CT burden (2 ohm,B-2 burden) as given in Table 9, IEEE C57.13. Will the actual value be normally 1/4 th of standard value for all CTs..?






RE: CT accuracy class for Transformer differential protection per IEEE
I don't have the example at hand, but in a wye connection there is no current in the neutral for balanced operation. With no current it doesn't much matter what the burden of that conductor might be.
RE: CT accuracy class for Transformer differential protection per IEEE
Most differential relay instruction books will have worked examples also.
RE: CT accuracy class for Transformer differential protection per IEEE
Also found the answer for the CT burden given in the worked example. The given values are actual CT secondary resistance values which are naturally less than standard CT burden.
But the typial excitation curve(shown in IEEE Std) doesn't have the CT secondary resistance value for 2000/5A CTs.Can any one provide me the approximate secondary resistance value for 2000/5A CTs.?
RE: CT accuracy class for Transformer differential protection per IEEE