ABB Relion 670 series - Page 420

en06000618.vsd
X
11
X
12
-
jX
C
A B
D
A
D
B
Zone 1
A
Zone 1
B
Zone 2
A
Zone 2
B
G
IEC06000618 V1 EN
Figure 211: Underreaching (Zone 1) and overreaching (Zone 2) on series
compensated line
The underreaching zone will have reduced reach in cases of bypassed series capacitor, as
shown in the dashed line in figure
93. The overreaching zone (Zone 2) can this way cover
bigger portion of the protected line, but must always cover with certain margin the remote
end bus. Distance protection Zone 1 is often set to
( )
1 11 12
= × + -
Z S C
X K X X X
EQUATION1914 V1 EN (Equation 370)
Here K
S
is a safety factor, presented graphically in figure 94, which covers for possible
overreaching due to low frequency (sub-harmonic) oscillations. Here it should be noted
separately that compensation degree K
C
in figure
94 relates to total system reactance,
inclusive line and source impedance reactance. The same setting applies regardless MOV
or spark gaps are used for capacitor overvoltage protection.
Equation 66 is applicable for the case when the VTs are located on the bus side of series
capacitor. It is possible to remove X
C
from the equation in cases of VTs installed in line
side, but it is still necessary to consider the safety factor K
S
.
If the capacitor is out of service or bypassed, the reach with these settings can be less than
50% of protected line dependent on compensation degree and there will be a section, G in
figure 93, of the power line where no tripping occurs from either end.
en06000619.vsd
K
S
1.0
0.8
0.6
0.4
0.2
0 20 40 60 80 100
K
C
[%]
IEC06000619 V1 EN
Figure 212: Underreaching safety factor K
S
in dependence on system compensation
degree K
C
Section 8 1MRK 506 369-UUS -
Impedance protection
414 Line distance protection REL670 2.2 ANSI
Application manual