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~~
R
1
R
fault
X
1
R
N
X
N
~~
R
1
X
1
~~
R
1
X
1
V
L1
V
L2
V
L3
Fault loops
AG, BG
and CG
I
F
I
F
Fault loops
AB, BC and CA
I
F
I
F
R
fault
Fault loop
ABC
I
F
I
F
I
F
R
fault
R
fault
A
B
C
N
E
R
fault
/2
R
fault
/2
GUID-5CD4F4DA-2CC5-4432-856B-B4A6C5A739B4 V1 EN
Figure 415:
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 ground faults. All ground-fault distance calculation algorithms of
21FL 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. 21FL 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 ground 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
-
GUID-2F67A337-58A8-40F4-B752-678A8D89083E V1 EN
(Equation 150)
x
fault
Corresponds to the signal value during fault
x
pre-fault
Corresponds to the signal value during healthy state just before fault
1MAC059074-MB A
Section 5
Protection related functions
615 series ANSI
813
Technical Manual
Содержание Relion 615 series
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