ABB REG670 - Zone Reach Setting Lower than Minimum Load Impedance


1
R 2 R1Zx R0Zx RFPEZx
3
  
IECEQUATION2303 V2 EN (Equation 68)
2X1Zx X0Zx
arctan
2 R1Zx R0Zx
loop










EQUATION2304 V2 EN (Equation 69)
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 70)
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 zone1 reach in the resistive direction for phase-to-phase loop
measurement based on equation 71.
61
R
FPPZx X Zx


IECEQUATION2306 V3 EN (Equation 71)
The setting XLd is primarily there to define the border between what is considered a
fault and what is just normal operation. See figure 92 In this context, the main
examples of normal operation are reactive load from reactive power compensation
equipment or the capacitive charging of a long high-voltage power line. XLd needs to
be set with some margin towards normal apparent reactance; not more than 90% of the
said reactance or just as much as is needed from a zone reach point of view.
As with the settings RLdFw and RLdRv
[2]
, XLd is representing a per-phase load
impedance of a symmetrical star-coupled representation. For a symmetrical load or
three-phase and phase-to-phase faults, this means per-phase, or positive-sequence,
impedance. During a phase-to-earth fault, it means the per-loop impedance, including
the earth return impedance.
8.2.3.7 Zone reach setting lower than minimum load impedance
Even if the resistive reach of all protection zones is set lower than the lowest expected
load impedance and there is no risk for load encroachment, it is still necessary to set
RLdFw, RLdRv
[3]
and ArgLd according to the expected load situation, since these
settings are used internally in the function as reference points to improve the
performance of the phase selection.
The maximum permissible resistive reach for any zone must be checked 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 with equation
72.
[2] RLdRv=RLdRvFactor*RLdFw
[3] RLdRv=RLdRvFactor*RLdFw
1MRK 502 071-UEN - Section 8
Impedance protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 207
Application manual