ABB Relion 670 Series Applications Manual page 250

Section 10
Unbalance protection
L1
Faulty unit
Cx Cx Cx Cx
Cu Cu Cu
C1
Cu
Cu Cu
U1
Cu Cu Cu
C
Cu Cu Cu
IEC19000591 V1 EN-US
Figure 116: Units arrangement in a phase L1 of H-bridge connected capacitor bank
Assume that the voltage at the filter terminal is maintained at 1 p.u. The unbalance current is
calculated based on the number of fuse operations. The failure of the capacitor elements are
due to fuse operation (open-circuit). For further analysis, considering capacitor failure has
occurred only in the first unit of the first quadrant of L1 phase .
The capacitance values in the system are calculated by using the following equations:
P
=
C
u
S
IECEQUATION19037 V1 EN-US
where, C
Whenever an element failure occurs, the capacitance of the unit changes to:
æ
=
ç
C
ç
x
è
IECEQUATION19038 V1 EN-US
Where,
f is the number of fuse blown
e
C is the capacitance of the faulty unit
x
If an element fails in a unit, the capacitance of the quadrant changes to:
244
IL
1
Cu
Cu Cu Cu Cu
Cu Cu Cu Cu Cu
I
UN BL 1
Cu
Cu Cu Cu Cu
Cu Cu Cu Cu
Cu
´ = ´
e
C 9.5 C
e e
e
is the capacitance of one unit
u
( )
ö
- ´
P f P
´
e e e ÷
÷
( ) ( )
- ´ - +
P f S 1 P ø
e e e e
© Copyright 2017 Hitachi Power Grids. All rights reserved
Cu Cu Cu Cu Cu
Cu
Cu Cu Cu Cu
U2
Cu Cu Cu Cu Cu
Cu Cu Cu Cu Cu
C
e
1MRK 511 401-UEN Rev. K
Pe
19 parallel string
Ce
Cu
Se
19 parallel string 19 parallel string
Cu
Ce Ce
Cu
Cu
Bay control REC670
Application manual
1MΩ
Ce
Ce
1MΩ 1MΩ
Ce Ce Ce Ce
IEC19000591-1-en-us.vsdx
(Equation 119)
(Equation 120)