The recorded data Flt phase reactance provides the estimated positive-sequence
reactance from the substation to the fault location.
Figure 444: 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
, where the load is assumed to be evenly
distributed along the feeder, resulting in the actual voltage drop curve as seen in
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
drop
(real), appears at the end
of 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
drop
(real). The dashed curve shows the voltage drop profile in this case.
1MRS757644 H
Protection related functions
620 series
Technical Manual
839
