Function Block - ABB 615 series Technical Manual

Section 5
Protection related functions
5.7.2
5.7.3
5.7.4
804

Function block

21FL
I_A ALARM
I_B
I_C
I
0
I
1
I
2
V_A_AB
V_B_BC
V_C_CA
V
0
V
1
V
2
BLOCK
TRIGG
TRIGG_XC0F
GUID-942FCEAA-203A-4616-B703-9A792A8FB69A V1 EN
Figure 409: Function block
Functionality
The fault locator function 21FL provides impedance-based fault location. It is designed
for radially operated distribution systems. It is applicable for locating short circuits in all
kinds of distribution networks. Ground faults can be located in effectively grounded and
in low-resistance or low-reactance grounded networks. Under certain limitations, 21FL
can also be applied for an ground-fault location in ungrounded distribution networks.
The fault distance calculation is based on locally measured fundamental frequency current
and voltage phasors. The full operation of 21FL requires that all phase currents and phase-
to-ground voltages are measured.
The fault distance estimate is obtained when the function is externally or internally
triggered.
Operation principle
The fault distance calculation is done in two steps. First, the fault type is determined with
the inbuilt Phase Selection Logic (PSL). Second, based on the selected impedance
measuring element (fault loop) the fault distance from the measuring point to the fault
location is calculated.
As a fundamental operation criterion, the phase current and voltage magnitudes must
exceed the threshold values of 2% xIn and 3% xUn, respectively.
The function can be enabled or disabled with the Operation setting. The corresponding
parameter values are "Enable" and "Disable".
1MAC059074-MB A
615 series ANSI
Technical Manual