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min
2
1
0
0.8
cos
sin
2
1
0
load
R
R
RFPE
Z
X
X
J
J
×
+
£
×
×
-
×
×
+
é
ù
ê
ú
ë
û
EQUATION578 V4 EN-US
(Equation 351)
Where:
∂
is a maximum load-impedance angle, related to the maximum load power.
To avoid load encroachment for the phase-to-phase measuring elements, the set resistive
reach of any distance protection zone must be less than 160% of the minimum load
impedance.
RFPP 1.6 Zload
£
×
load
1.6 Z
£
×
RFPP
EQUATION579 V2 EN-US
(Equation 352)
Equation
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. For
other cases a more accurate calculations are necessary according to equation
load min
R1
RFPP 1.6 Z
cos
sin
X1
J
J
£
×
-
×
é
ù
× ê
ú
ë
û
IECEQUATION2307 V1 EN-US
(Equation 353)
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.
7.12.3.8
Zone reach setting higher than minimum load impedance
GUID-78D0227F-2568-4C9A-8921-45812B4ABAF2 v4
The impedance zones are enabled as soon as the (symmetrical) load impedance crosses the
vertical boundaries defined by
RLdFw and RLdRv
[4]
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.
min
0.9
load
RLdFw
R
<
×
IECEQUATION2419 V2 EN-US
(Equation 354)
min
0.9
load
RLdRv
R
<
×
IECEQUATION2420 V2 EN-US
(Equation 355)
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,
[4] RLdRv=RLdRvFactor*RLdFw
Section 7
1MRK 505 343-UEN B
Impedance protection
320
Application manual
Summary of Contents for Relion 670 series
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