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functionality is not needed (that is, when the load is not encroaching on the distance zones).
Always define the load encroachment boundary according to the actual load or in
consideration of how far the phase selection must actually reach.
7.13.4.8
Load impedance limitation, without load encroachment function
GUID-16C2EB30-7FEA-42E4-98C8-52CCC36644C6 v4
The following instructions are valid when setting the resistive reach of the distance zone itself
with a sufficient margin towards the maximum load, that is, without the common load
encroachment characteristic (set by
RLdFw, RLdRv
[8]
and
ArgLd). Observe that even though
the zones themselves are set with a margin,
RLdFw and RLDRVFactor still have to be set
according to maximum load for the phase selection to achieve the expected performance.
Check the maximum permissible resistive reach for any zone to ensure that there is a sufficient
setting margin between the boundary and the minimum load impedance. The minimum load
impedance (Ω/phase) is calculated as:
Z
loadmin
U
2
S
-------
=
EQUATION571 V1 EN-US
(Equation 416)
Where:
U
is the minimum phase-to-phase voltage in kV
S
is the maximum apparent power in MVA.
The load impedance [Ω/phase] is a function of the minimum operation voltage and the
maximum load current:
Z
load
U
min
3 I
max
×
----------------------
=
EQUATION574 V1 EN-US
(Equation 417)
Minimum voltage U
min
and maximum current I
max
are related to the same operating
conditions. Minimum load impedance occurs normally under emergency conditions.
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.
RFPE 0.8 Z
load
×
£
EQUATION792 V1 EN-US
(Equation 418)
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
.
[8] RLdRv=RLdRvFactor*RLdFw.
Section 7
1MRK 505 343-UEN B
Impedance protection
360
Application manual
Summary of Contents for Relion 670 series
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