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 98)
Where:
ϑ is a maximum load-impedance angle, related to the minimum load impedance conditions.
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 99)
Equation 99 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 100.
RFPP 1.6 Z
loadmin
cos
J
R1PP
X1PP
---------------–
sin
J×× ×£
EQUATION580 V1 EN-US (Equation 100)
All this is applicable for all measuring zones when no power swing detection element
is in the protection scheme. Use an additional safety margin of approximately 20% in
cases when a power swing detection element is in the protection scheme, refer to the
description of Power swing detection (ZMRPSB
, 68) function.
8.1.3.9 Load impedance limitation, with load encroachment function activated
SEMOD168247-129 v2
The parameters for load encroachment shaping of the characteristic are found in the
description of the phase selection with load encroachment function, section
"Setting
guidelines". If the characteristic for the impedance measurement is shaped with the
load encroachment algorithm, the parameter RLdFw and the corresponding load angle
ArgLd
must be set according to the minimum load impedance.
8.1.3.10 Setting of minimum operating currents
SEMOD168247-132 v2
The operation of the distance function can be blocked if the magnitude of the currents
is below the set value of the parameter IMinPUPP and IMinPUPG.
1MRK 504 163-UUS A Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 247
Application manual
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