times the load-impedance angle, more accurate calculations are necessary according to
equation
min
2
1
0
0.8
cos
sin
2
1
0
×
+
£
×
×
¶ -
×
¶
×
+
é
ù
ê
ú
ë
û
load
R
R
RFPG
Z
X
X
GUID-11DD90FA-8FB5-425F-A46F-6553C00025BE V1 EN-US
(Equation 366)
Where:
ϑ
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.
load
1.6 Z
RFPPZx
EQUATION579 V3 EN-US
(Equation 367)
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. More accurate calculations are necessary according to equation
load min
R1Zx
RFPPZx
1.6 Z
cos
sin
X1Zx
IECEQUATION2307 V2 EN-US
(Equation 368)
All this is applicable for all measuring zones when no Power swing detection function
ZMRPSB (78) is activated in the IED. Use an additional safety margin of
approximately 20% in cases when a ZMRPSB (78) function is activated in the IED,
refer to the description of Power swing detection function ZMRPSB (78).
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
RLdFwd
and
RldRev
or the lines defined by
ArgLd
.
So, it is necessary to consider some margin. It is recommended to set
RLdFwd
and
RldRev
to 90% of the per-phase resistance that corresponds to maximum load.
The absolute value of the margin to the closest
LdAngle
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
Section 8
1MRK 504 163-UUS A
Impedance protection
444
Transformer protection RET670 2.2 ANSI
Application manual
Summary of Contents for RELION RET670
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