Figure 448: Definition of a physical fault point resistance in different fault loops
Steady-state asymmetry and load compensation
In reality, power systems are never perfectly symmetrical. The asymmetry produces
steady-state quantities in the form of zero-sequence and negative-sequence
voltages and currents. If not compensated, these are error sources for fault
distance calculation especially in case of earth faults. All earth-fault distance
calculation algorithms of SCEFRFLO utilize the delta-quantities which mitigate the
effects of the steady-state asymmetry.
Load current is another error source for fault distance calculation. Its influence
increases with higher fault resistance values. SCEFRFLO employs independent load
compensation methods for each fault type to achieve optimal performance. The
purpose of load compensation is to improve the accuracy of the fault distance
calculation models by estimating the actual fault current in the fault location. Delta-
quantities are used for this to mitigate the effect of load current on fault distance
estimation. For earth faults, the load compensation is done automatically inside
the fault distance calculation algorithm. For short circuit faults, load compensation
is enabled with setting
Load Com PP loops. The default value is “Enabled”. The
parameter should be set to “Disabled” only if the ratio between the expected fault
current and load current is large or when the fault distance estimate for short
circuit fault is required for each shot of an autoreclosing sequence.
The delta-quantity describes the change in measured signal due to the fault.
∆ =
+
x
x
x
fault
pre fault
-
(Equation 165)
x
fault
Corresponds to the signal value during fault
x
pre-fault
Corresponds to the signal value during healthy state just before fault
Result quality indicator
The quality of the estimated fault distance is judged and reported in recorded
data as the Flt Dist quality together with the fault distance estimate. The Flt
Dist quality is a bit vector indicating detected sources of inaccuracy in the fault
distance estimate. In case Flt Dist quality equals 1, the result is not affected by error
sources. This results in good quality for fault distance estimate. If factors affecting
Protection related functions
1MRS757644 H
844
620 series
Technical Manual
