GE L90 Instruction Manual page 803

Line current differential system
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CHAPTER 10: THEORY OF OPERATION
If the
FAULT REPORT 1 VT SUBSTITUTION
location is performed based on the actual phase to ground voltages. If the VTs are connected in a delta configuration, fault
location is performed based on the delta voltages and zero-sequence voltage approximated based on the zero-sequence
current:
where Z
is the equivalent zero-sequence impedance behind the relay as entered under the fault report setting menu.
SYS0
Since the fault locator algorithm is based on the single-end measurement method, in three-terminal configuration
the estimation of fault location may not be correct at all three terminals especially if fault occurs behind the line's
tap respective to the given relay.
L90 LINE CURRENT DIFFERENTIAL SYSTEM – INSTRUCTION MANUAL
setting value is "I0" and the VTs are connected in a wye configuration, the fault
Figure 10-20: Fault locator scheme
FAULT LOCATOR
Eq. 10-84
10
10-61

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