EQUATION579 V3 EN-US (Equation 397)
Equation 397 is applicable only when the loop characteristic angle for the phase-to-
phase faults is more than three times as large as the maximum expected load-
impedance angle. More accurate calculations are necessary according to
equation 398.
load min
R1Zx
RFPPZx 1.6 Z cos sin
X1Zx
IECEQUATION2307 V2 EN-US (Equation 398)
All this is applicable for all measuring zones when no Power swing detection
function ZMRPSB is activated in the IED. Use an additional safety margin of
approximately 20% in cases when a ZMRPSB function is activated in the IED,
refer to the description of Power swing detection function ZMRPSB.
8.13.4.9 Zone reach setting higher than minimum load impedance
GUID-78D0227F-2568-4C9A-8921-45812B4ABAF2 v5
The impedance zones are enabled as soon as the (symmetrical) load impedance
crosses the vertical boundaries defined by RLdFw and RLdRv
[9]
or the lines
defined by ArgLd. So, it is necessary to consider some margin. It is recommended
to set RLdFw and RLdRv to 90% of the per-phase resistance that corresponds to
maximum load.
IECEQUATION2419 V2 EN-US (Equation 399)
IECEQUATION2420 V2 EN-US (Equation 400)
The absolute value of the margin to the closest ArgLd line should be of the same
order, that is, at least 0.1 • Z
load min
.
The load encroachment settings are related to a per-phase load impedance in a
symmetrical star-coupled representation. For symmetrical load or three-phase and
phase-to-phase faults, this corresponds to the per-phase, or positive-sequence,
impedance. For a phase-to-earth fault, it corresponds to the per-loop impedance,
including the earth return impedance.
[9] RLdRv=RLdRvFactor*RLdFw
1MRK 506 369-UEN B Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 403
Application manual
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