both phase-to-phase and phase-to-earth fault operating
characteristics should be considered.
To avoid load encroachment for the phase-to-earth measuring elements, the set
resistive reach of any distance protection zone must be less than 80% of the
minimum load impedance.
EQUATION792 V2 EN-US (Equation 69)
Equation 69 is applicable only when the loop characteristic angle for the single
phase-to-earth 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
70.
min
21 0
0.8 cos sin
21 0
load
RZx R Zx
RFPEZx Z
XZx XZx
EQUATION578 V5 EN-US (Equation 70)
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 71)
Equation
71 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
72.
load min
R1Zx
RFPPZx 1.6 Z cos sin
X1Zx
IECEQUATION2307 V2 EN-US (Equation 72)
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.
Section 7 1MRK 505 393-UEN B
Impedance protection
128 Line differential protection RED650 2.2 IEC
Application manual
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