ABB RELION Series Technical Manual page 492

Section 5
Protection related functions
486
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Figure 250: Fault loop impedance for phase-to-earth fault loops "AG Fault", "BG
Fault" or "CG Fault"
The earth-fault distance calculation algorithm is selected with setting EF algorithm
Sel. Options for the selection are "Load compensation" and "Load modelling". For the
correct operation of both algorithms there should not be any zero-sequence current
sources, for example, earthing transformers, in front of the protection relay location.
The "Load compensation" algorithm utilizes symmetrical components to compensate
for the effect of load on the measured voltages and currents. In case of radial feeders,
this algorithm should be selected with low-impedance/effectively earthed systems
where the fault current is fed from one side only and there are no in-feeds along the
protected line.
The "Load modelling" algorithm takes into account the effect of the load in the
measured currents and voltages by considering it in the fault loop model. In case of
radial feeders, this algorithm can be applied with low-impedance/effectively earthed
systems where the fault current is fed from one side only. The "Load modelling"
algorithm has been especially designed for unearthed systems.
The "Load modelling" algorithm requires the Equivalent load Dis setting, that is, an
equivalent load distance, as an additional parameter. The derivation and meaning of
this parameter is illustrated in
distributed along the feeder, resulting in the actual voltage drop curve as seen in the
middle part of Figure 251.
In case of evenly distributed load, Equivalent load Dis ~ 0.5. When the load is tapped
at the end of the feeder, Equivalent load Dis = 1.0. If the load distribution is unknown,
a default value of 0.5 can be used for Equivalent load Dis.
The maximum value of the voltage drop, denoted as U
the feeder. The Equivalent load Dis parameter is the distance at which a single load tap
corresponding to the total load of the feeder would result in a voltage drop equal to
U (real). The dashed curve shows the voltage drop profile in this case.
drop
Figure 251, where the load is assumed to be evenly
drop
1MRS758755 A
(real), appears at the end of
REC615 and RER615
Technical Manual