ABB RELION 670 Series Applications Manual page 335

1MRK 504 152-UEN B
=
X K
Z 1
EQUATION1914 V1 EN-US
Here K
S
overreaching due to low frequency (sub-harmonic) oscillations. Here it should be noted
separately that compensation degree K
inclusive line and source impedance reactance. The same setting applies regardless MOV or
spark gaps are used for capacitor overvoltage protection.
Equation
capacitor. It is possible to remove X
but it is still necessary to consider the safety factor K
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 200, of the power line where no tripping occurs from either end.
1.0
0.8
0.6
0.4
0.2
0
IEC06000619 V1 EN-US
Figure 201: Underreaching safety factor K
For that reason permissive underreaching schemes can hardly be used as a main protection.
Permissive overreaching distance protection or some kind of directional or unit protection
must be used.
The overreach must be of an order so it overreaches when the capacitor is bypassed or out of
service. Figure
the total protection but it only has the feature of a back-up protection for close up faults. The
overreach is usually of the same order as the permissive zone. When the capacitor is in
operation the permissive zone will have a very high degree of overreach which can be
considered as a disadvantage from a security point of view.
A
IEC06000620 V1 EN-US
Figure 202: Permissive overreach distance protection scheme
Negative IED impedance, positive fault current (voltage inversion)
Assume in equation
<
X X
11
EQUATION1898 V1 EN-US
Application manual
( )
× + -
X X X
S 11 12 C
is a safety factor, presented graphically in figure 201, which covers for possible
348 is applicable for the case when the VTs are located on the bus side of series
20 40 60
degree K
C
202 shows the permissive zones. The first underreaching zone can be kept in
- jX
Permissive Zone
C A
X
11
Permissive Zone
B
D
A
349
< +
X X
C S 11
in figure 201 relates to total system reactance,
C
from the equation in cases of VTs installed in line side,
C
.
S
80 100
K [%]
C
en06000619.vsd
in dependence on system compensation
S
B
X
12
D
B
en06000620.vsd
Section 7
Impedance protection
(Equation 348)
GUID-4FB71D72-36F1-4FCD-9321-D069CF6E9835 v2
(Equation 349)
329