ABB 615 series Technical Manual page 814

Section 5
Protection related functions
808
GUID-B455F553-4F09-442D-9297-4262002D5D07 V2 EN
Figure 411: Fault loop impedance for phase-to-ground fault loops "AG Fault", "BG
Fault" or "CG Fault"
The ground-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, grounding 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 grounded 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 grounded systems where
the fault current is fed from one side only. The "Load modelling" algorithm has been
especially designed for ungrounded 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
along the feeder, resulting in the actual voltage drop curve as seen in the middle part of
Figure 412.
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 V
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
V (real). The dashed curve shows the voltage drop profile in this case.
drop
Figure 412, where the load is assumed to be evenly distributed
1MAC059074-MB A
(real), appears at the end of the
drop
615 series ANSI
Technical Manual