ABB REG670 - Load Impedance Limitation, Without Load Encroachment Function

2X1Zx X0Zx
arctan
2 R1Zx R0Zx
loop










EQUATION2304 V2 EN (Equation 137)
Setting of the resistive reach for the underreaching zone 1 should follow the condition
to minimize the risk for overreaching:
RFPEZx 4.5 X1Zx


IECEQUATION2305 V2 EN (Equation 138)
The fault resistance for phase-to-phase faults is normally quite low, compared to the
fault resistance for phase-to-earth faults. To minimize the risk for overreaching, limit
the setting of the zone 1 reach in resistive direction for phase-to-phase loop
measurement to:
61
R
FPPZx X Zx


IECEQUATION2306 V3 EN (Equation 139)
Note that
RLdFw and RLdRv
[7]
are not only defining the load encroachment
boundary. They are used internally as reference points to improve the performance of
the phase selection. In addition, they define the impedance area where the phase
selection element gives indications, so do not set RLdFw and RLDRVFactor to
excessive values even if the load encroachment functionality is not needed (that is,
when the load is not encroaching on the distance zones). Always define the load
encroachment boundary according to the actual load or in consideration of how far the
phase selection must actually reach.
8.3.4.8 Load impedance limitation, without load encroachment function
The following instructions are valid when setting the resistive reach of the distance
zone itself with a sufficient margin towards the maximum load, that is, without the
common load encroachment characteristic (set by RLdFw, RLdRv
[8]
and ArgLd).
Observe that even though the zones themselves are set with a margin, RLdFw and
RLdRvFactor still have to be set according to maximum load for the phase selection
to achieve the expected performance.
Check the maximum permissible resistive reach for any zone to ensure that there is a
sufficient setting margin between the boundary and the minimum load impedance.
The minimum load impedance (Ω/phase) is calculated as:
[7] RLdRv=RLdRvFactor*RLdFw.
[8] RLdRv=RLdRvFactor*RLdFw.
Section 8 1MRK 502 071-UEN -
Impedance protection
256 Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual