ABB RELION REX640, Technical Manual, Page: 1199 / 1960

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
Figure 684
, where the load is assumed to be evenly
distributed along the feeder, resulting in the actual voltage drop curve as seen in the
middle part of
Figure 684
.
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 setting is the distance at which a single load
tap corresponding to the total load of the feeder results in a voltage drop equal to
U
drop
(real). The dashed curve shows the voltage drop profile in this case.
Figure 684: Description of the equivalent load distance
The exact value for
Equivalent load Dis can be calculated based on the load flow and
voltage drop calculations using data from DMS-system and the following equation.
1MRS759142 F Protection related functions
REX640
Technical Manual
1199