ABB RELION 620 Series Technical Manual page 889

1MAC504801-IB E
620 series ANSI
Technical Manual
Requirements for measurement transformers
recommended that all the CTs have an identical constructions, that is, they have an equal
burden and characteristics and are of the same type, preferably from the same
manufacturing batch. If the CT characteristics and burden values are not equal,
calculations for each branch in the scheme should be performed separately and the worst-
case results should be used. In
branches are not equal, and hence, the maximum burden equal to 3.2Ω should be used for
calculating the stabilized voltage.
GUID-B9FC1162-06E4-4FCF-B093-0A503ECFC0B1 V1 EN
Figure 459: High-impedance busbar differential protection with different CT burden
value on each feeder
First, the stabilizing voltage, that is, the voltage appearing across the measuring branch
during the out-of-zone fault, is calculated assuming that one of the parallel connected CT
is fully saturated. The stabilizing voltage can be calculated with
Figure 227, the CT winding resistance and the burden of the
Section 13
Equation 55.
883