ABB REL 551 2.3 Series Installation And Comissioning Manual page 109

Line differential protection (DIFL)
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Read the values of the differential and bias currents under the
menu:
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They must correspond to the value:
IDiffL1 IDiffL2 IDiffL3
= =
I = I for each phase.
Diff Bias
U Represents measured phase voltage.
The bias currents are available under the same menu. They must
be equal to the measured differential current in each phase.
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They must correspond to the following values:
IDiffL1 = IDiffL2 = IDiffL3
IBiasL1 = IBiasL2 = IBiasL3
U
------------------------------------------- -
=
⋅
XC1 CTFactor
⋅
2 U
------------------------------------------- -
=
⋅
XC0 CTFactor
U
= ------------------------------------------- -
⋅
XC0 CTFactor
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(Equation 8)
(Equation 9)
(Equation 10)
103