min
2 1 0
0.8 cos sin
2 1 0
load
R R
RFPG Z
X X
× +
£ × × ¶ - × ¶
× +
é ù
ê ú
ë û
EQUATION1721 V2 EN-US (Equation 72)
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.
EQUATION579 V3 EN-US (Equation 73)
Equation 73 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 74.
load min
R1Zx
RFPPZx 1.6 Z cos sin
X1Zx
IECEQUATION2307 V2 EN-US (Equation 74)
8.2.3.8 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 mar
gin. 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
phase-to-phase faults, this corresponds to the per-phase, or positive-sequence,
impedance. For a phase-to-ground fault, it corresponds to the per-loop impedance,
including the ground return impedance.
1MRK 502 071-UUS A Section 8
Impedance protection
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062 223
Application manual
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