ABB Relion 670 series - Load Impedance Limitation, Without Load Encroachment Function430

8.13.4.8 Load impedance limitation, without load encroachment function
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 RLdFwd, RldRev and ArgLd). Observe that even
though the zones themselves are set with a margin, RLdFwd and RldRev 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:
2
loa d min
Z
V
S
=
EQUATION1718 V1 EN (Equation 394)
Where:
V 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:
min
loa d
ma x
Z
V
3 I
=
×
EQUATION1719 V1 EN (Equation 395)
Minimum voltage V
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-ground measuring elements, the set resistive
reach of any distance protection zone must be less than 80% of the minimum load
impedance.
0.8
£ × loadRFPG Z
GUID-AD2F1BE2-8442-4ED1-A558-21D092CEE170 V1 EN
(Equation 396)
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 146.
Section 8 1MRK 506 369-UUS -
Impedance protection
430 Line distance protection REL670 2.2 ANSI
Application manual