ABB 615 series Technical Manual page 819

1MAC059074-MB A
615 series ANSI
Technical Manual
R
V
1
L1
~ ~
A
R
V
1
L2
~ ~
B
R
V
1
L3
~ ~
C
N
R
N
E
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
x Corresponds to the signal value during fault
fault
x Corresponds to the signal value during healthy state just before fault
pre-fault
Protection related functions
Fault loops
AG, BG
and CG
X I
1 F
X
R
1 fault
X
1
I
F
X
N
Section 5
Fault loops
Fault loop
AB, BC and CA
ABC
I I
F F
R /2 R
fault
I I
F F
R /2 R
I fault
fault
F
(Equation 150)
fault
R
fault
813