IEC08000437 V1 EN-US
Figure 141: Rotation of load characteristic for a fault between two phases
There is a gain in selectivity by using the same measurement as for the quadrilateral characteristic
since not all phase-to-phase loops will be fully affected by a fault between two phases. It should
also provide better fault resistive coverage in quadrant one. The relative loss of fault resistive
coverage in quadrant four should not be a problem even for applications on series compensated
lines.
7.7.6.5 Minimum operate currents
GUID-7F780AC7-36AB-4704-843D-C1EA3F5B2D6A v1
The operation of Phase selection, quadrilateral characteristic with settable angle (FRPSPDIS, 21) is
blocked if the magnitude of input currents falls below certain threshold values.
The phase-to-ground loop n is blocked if In<
IMinPUPG
, where In is the RMS value of the current in
phase n (A or B or C).
The phase-to-phase loop mn is blocked if (2·In<
IMinOpPPIMinPUPP
).
7.7.6.6 Simplified logic diagrams
GUID-95AD1A91-86F0-4854-A12B-99C504BFBC6C v1
Figure 142 presents schematically the creation of the phase-to-phase and phase-to-ground
operating conditions. Consider only the corresponding part of measuring and logic circuits, when
only a phase-to-ground or phase-to-phase measurement is available within the IED.
1MRK 502 066-UUS B Section 7
Impedance protection
285
Technical manual
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