ABB Relion 670 Series Applications Manual page 260

Section 10
Unbalance protection
27.43 MVAR
88 kV
IEC19000654 V1 EN-US
Figure 121: Single line diagram for grounded single WYE capacitor bank
The configuration of capacitor unit (Cu) and capacitor element (Ce) in the filter are shown in
Figure 122.
U
L1
U
L1Tap
IEC19000723 V1 EN-US
Figure 122: Units and elements arrangement in grounded single WYE connected capacitor bank
Assume that the voltage at the filter terminal is maintained at 1 pu. The differential voltage is
calculated based on the number of fuse operations. The failure of the capacitor elements are
due to the fuse operation (open-circuit). For further analysis, considering that the capacitor
failure has occurred in a section above the tap point of phase L1 as shown in
stored voltage ratio for calculation of differential voltage for phase L1 (USEDURATL1) is 0.5.
The capacitance values in the system are calculated by using the following equations:
254
88 kV Bus
88 kV Bus
Faulty Unit
C
x
C
1
Tap
C
C
u
C
2
P
u
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Preprocessing Function
Block
SMAI1
GRP1Lx G1AI3P
SMAI2
GRP2Lx G2AI3P
Lx = Phase L1, L2 and L3
C
C
u
u
Su
C
u
u
1MRK 511 401-UEN Rev. K
SCPDPTOV
U3P
U3PTAP
IED
IEC19000654-1-en.vsdx
Single Capacitor Unit
C C C
e e e
C C C
e e e
C C C
e e e
P
e
IEC19000723-1-en.vsdx
Figure 122. The
Bay control REC670
Application manual
S
e