This equation is applicable only when the loop characteristic angle for the single phase-to-
ground faults is more than three times as large as the maximum expected load-impedance
angle. For the case when the loop characteristic angle is less than three times the load-
impedance angle, more accurate calculations are necessary according to equation
54.
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 (Equation 54)
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 V2 EN (Equation 55)
Equation 55 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
56.
loadmin
R1
RFPP 1.6 Z cos sin
X1
J J
£ × - ×
é ù
×
ê ú
ë û
IECEQUATION2307 V1 EN (Equation 56)
All this is applicable for all measuring zones when no Power swing detection function
ZMRPSB (68) is activated in the IED. Use an additional safety margin of approximately
20% in cases when a ZMRPSB (68) function is activated in the IED, refer to the
description of Power swing detection function ZMRPSB (68).
Load impedance limitation, with Phase selection with load encroachment,
quadrilateral characteristic function activated
The parameters for shaping of the load encroachment characteristic are found in the
description of Phase selection with load encroachment, quadrilateral characteristic
function (FDPSPDIS, 21).
1MRK 506 334-UUS A Section 6
Impedance protection
137
Application manual
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