ABB RET670 Applications Manual page 179

1MRK504116-UUS C
Application manual
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Parallel line out of service and not grounded
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ANSI05000223 V1 EN
Figure 55: Parallel line is out of service and not grounded
When the parallel line is out of service and not grounded, the zero sequence on that
line can only flow through the line admittance to the ground. The line admittance is
high which limits the zero-sequence current on the parallel line to very low values. In
practice, the equivalent zero-sequence impedance circuit for faults at the remote bus
bar can be simplified to the circuit shown in figure
The line zero sequence mutual impedance does not influence the measurement of the
distance protection in a faulty circuit. This means that the reach of the underreaching
distance protection zone is reduced if, due to operating conditions, the equivalent zero
sequence impedance is set according to the conditions when the parallel system is out
of operation and grounded at both ends.
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en05000223_ansi.vsd
Section 3
IED application
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(Equation 67)
(Equation 68)
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