ABB RELION 620 Series Technical Manual page 844

Section 5
Protection related functions
5.7.3
5.7.4
838
Functionality
The fault locator function SCEFRFLO 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. Earth faults can be located in effectively
earthed and in low-resistance or low-reactance earthed networks. Under certain
limitations, SCEFRFLO can also be applied for an earth-fault location in unearthed
distribution networks.
The fault distance calculation is based on locally measured fundamental frequency
current and voltage phasors. The full operation of SCEFRFLO requires that all phase
currents and phase-to-earth 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 "On" and "Off".
The operation of SCEFRFLO can be described with a module diagram. All the
modules in the diagram are explained in the next sections.
GUID-FB1818E0-0F8D-4CBA-A55F-FC927CDA11C6 V2 EN
Figure 433: Functional module diagram
1MRS757644 F
620 series
Technical Manual