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1MRK 506 369-UEN B
Line distance protection REL670 2.2 IEC
Application manual
Minimum voltage U
min
operating conditions. Minimum load impedance occurs normally under emergency
conditions.
As a safety margin is required to avoid load encroachment under
three-phase conditions and to guarantee correct healthy phase IED
operation under combined heavy three-phase load and earth faults,
consider both: phase-to-phase and phase-to-earth fault operating
characteristics.
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.
RFPEZx
0.8
Z
load
EQUATION792 V2 EN-US
This equation 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 265.
RFPEZx
0.8
Z
cos
load
min
EQUATION578 V5 EN-US
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.
RFPPZx
1.6 Z
load
EQUATION579 V3 EN-US
Equation
266
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 267.
RFPPZx 1.6 Z
load min
IECEQUATION2307 V2 EN-US
and maximum current I
2
R Zx R Zx
1
0
sin
2
X Zx
1
X Zx
0
R1Zx
cos
sin
X1Zx
Section 8
Impedance protection
are related to the same
max
(Equation 264)
(Equation 265)
(Equation 266)
(Equation 267)
311
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