Siemens SENTRON 3VL series, Системное руководство

Страница: 67 / 360

Application planning
6.2 Use of capacitor banks
3VL molded-case circuit breakers
System Manual, 03/2009, 110 0110 - 02 DS 01
67
6.2 Use of capacitor banks
In general, reactive power compensation is used in order to reduce system losses and
voltage drops in the power distribution system. As a result, the power fed into the system is
used as active power and costs will be saved through a reduction in the capacitive and
inductive power factors.
A combination of fixed and central compensations are used depending on the design of the
low-voltage system and the loads involved.
Circuit breaker for protecting and switching capacitor banks
According to the relevant standards DIN VDE 0560 Part 41 / EN 60831-1 / IEC 70,
capacitors must function under normal operating conditions with the current having an r.m.s.
value up to 1.3 times the rated current of the capacitor. In addition, a further tolerance of up
to 15% of the real value of the power must be taken into consideration.
The maximum current with which the selected circuit breaker can be constantly loaded, and
which it must also be able to switch, is calculated as follows:
I
N max
= I
N
x 1.5 (r.m.s. value, r.m.s. current)
Important values for selecting circuit breakers
More detailed information in the technical data: Capacitor banks (Page 173)
Abbr. Designation
Q
n
Capacitor bank rated power in kVA
V
N
Rated voltage of the capacitor
I
N
Rated current of the capacitor bank
I
N max
Maximum expected rated current
I
i
Value for setting the instantaneous short-circuit release
I
R
Value for setting the current-dependent delayed overload release
The following applies:
I
N
= Q
N
/ √3 x V
N
I
R
= I
Nmax
= I
N
x 1.5
I
i
> 9 x I
R
(minimum)