Medium voltage switchgear application guide

Medium voltage switchgear application guide
Appendix 3: capacitor
(cont’d)
date
11/94
- B•3•2 -
revised
05/2004
4 - SWITCHING CURRENT
The current switching of the capacitance. current must always be lower than 100 times the rated
It is generally limited to 10 kA peak by impulse reactors.
The switching current value depends on the type of bank used. It is equal to:
1) for a single bank:
Ie = 1
L0 •C
Ie =Ic • 2 •
S •I L
A B
c • • 2 1ω
I c
k
G
U
Ie: C: peak-switching capacitance of one current
L0: network short-circuit tap
Sk: supply short-circuit power reactor in MVA
Qc: S capacitor = 3 •U •Isc bank with power U k
3 =L0 in Mvar
•Isc =U2
• ω
ω = 2 •π •ƒnetwork= network pulsation
2) for a multi-steps bank with n identical steps:
1 2 n + 1
l l l
C C C
U: Ie: peak-switching network phase to current
n: number of energized phase tapsvoltage
C: l: link capacitance reactor of one tap
ω = 2 •π •ƒnetwork= network pulsation
ƒinherent = 2
1
l • π • •C
C
L0 • ω
Qc
Ie =Ic • 2 •
Ie = 2
n + n1 ƒinherent
3 •U •
n + n
• ƒnetwork
1 c • l
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