Controlled Switching — Buyer´s Guide
D-3
Edition 2, 2006-09
Capacitor Banks and Harmonic Filters
Application
Switching of Capacitor Banks and Harmonic Filters
Staggering of Circuit Breakers
In case of a single-pole operated circuit
breaker, Switchsync
TM
will control each pole
individually to make it close at the right time.
For a three-pole operated circuit breaker,
with only one operating mechanism, the
poles are mechanically adjusted (staggered)
in order to close at the right instant. For
switching of a shunt capacitor bank or har-
monic filter, the actual choice of staggering
depends on:
- Connection of the neutral of the load -
grounded or ungrounded
- System frequency - 50 or 60 Hz
Staggering may also be arranged for other
applications, such as de-energizing of shunt
reactors.
Note:
Mechanical staggering of a circuit breaker will
affect both closing and opening times of the
individual poles. When staggering has been
chosen for control of closing operations,
opening operations will also be influenced.
The influence is small, however, and can
normally be disregarded.
There is one exception:
Staggered LTB 170D1/BUS circuit breakers
utilized for controlled closing of ungrounded
170 kV capacitor banks, also require
Switchsync
TM
control of opening operations,
in order to retain very low risk for restrikes.
Connection of Staggered Circuit
Breakers
It is important to observe that for correct
function, staggered circuit breakers intended
for
grounded
capacitor banks must be prop-
erly connected on site.
Correct connection depends on the circuit
breaker type and is illustrated in Figures 4
and 5 for the LTB 45D/BGS. With a posi-
tive phase sequence R-S-T of the supply
network, the phase-pole connections in this
case shall be:
Figure 4 and 5.
Connection of staggered LTB 145D1/BGS circuit
breaker for shunt capacitor bank with grounded
neutral.
If the recommended pole-phase connections
are not observed, it is impossible for all three
poles to close adjacent to their respective
voltage zeroes, and severe switching tran-
sients will be generated.
For staggered circuit breakers intended for
ungrounded capacitor banks, there is no
similar limitation to the phase-pole connec-
tions.
For permissible connections of staggered
circuit breakers, see the separate appendix.
Please contact ABB Power Technologies,
High Voltage Products, Ludvika, Sweden.
Control of Opening Operations
Opening of capacitor bank circuit breakers
generally does not lead to any significant
switching transients. The major reason is
that the circuit breakers are designed to have
very low risk of restrikes upon interruption of
capacitive current. However, in special cases
with severe conditions, the Switchsync
TM
may be utilized in controlled opening of ca-
pacitor bank circuit breakers. The aim is then
to eliminate the small statistical risk that a re-
strike may still occur, and the circuit breaker
is controlled in such a manner that short arc-
ing times are avoided.
R
S
T
Busbar
DS
Mechanically
Staggered
LTB 145 D1/BGS
Circuit Breaker
CT
Capacitor Bank
Grounded Neutral
C1
B1
A1
120
°
el.
R
S
T
B1
C1
A1
60
°
el.
Busbar
Voltage
Circuit
Breaker Pole
Staggering of Closing
Instant, El. Degrees
R
C
+60˚
S
B
0˚
T
A
+20˚
