ABB RET670 - Page 284

0
0 1
2 1 0
m
f
Z
K
Z Z R
= -
× + +
EQUATION1426 V1 EN (Equation 193)
If needed, enlarge the zone reach due to the reduction by mutual coupling. Consider
also the influence on the zone reach due to fault current infeed from adjacent lines.
Parallel line is out of service and grounded in both ends
Apply the same measures as in the case with a single set of setting parameters. This
means that an underreaching zone must not overreach the end of a protected circuit for
the single phase-to-ground faults.
The equivalent impedance will be according to equation 185.
Load impedance limitation, without load encroachment function
The following instruction is valid when the load encroachment function or blinder
function is not activated (BlinderMode=Disabled).The load encroachment function will
not be activated if RLdFw and RLdRv is set to a value higher than expected minimal
load impedance. If the load encroachment or blinder function is to be used for all or
some of the measuring zones, the load limitation for those zones according to this
chapter can be omitted. Check the maximum permissible resistive reach for any zone to
ensure that there is a sufficient setting margin between the relay boundary and the
minimum load impedance. The minimum load impedance (Ω/phase) is calculated as:
2
min
V
Zload
S
=
EQUATION1753-ANSI V1 EN (Equation 194)
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
max
3 I
V
Zload =
×
EQUATION1754-ANSI V1 EN (Equation 195)
Minimum voltage V
min
and maximum current I
max
are related to the same operating
conditions. Minimum load impedance occurs normally under emergency conditions.
Section 3 1MRK504116-UUS C
IED application
278
Application manual