Siemens SENTRON 3VL System Manual page 70

Application planning
6.4 Use in DC systems
Setting range of the trip values
● Thermal overload release:
Same setpoints as in 50 / 60 Hz networks.
● Instantaneous short circuit trip unit:
The response threshold increases by 30 to 40%.
Example:
At the I
Depending on the voltage, a series connection of 2, 3 or 4 current paths is required.
The following circuits are recommended since the current must flow through all current paths
in order to conform to the thermal tripping characteristic curves.
The thresold values of the instantaneous short-circuit release ("I" release) increase by 30 to
40%.
Suggested circuits for DC networks
Table 6- 2 Max. DC voltage Max. DC voltage for 3-pole circuit breakers
1 L+ 3 5
L-
2 4 6
NSE0_00741a
250 V DC
1 L+ 3 5 L-
2 4 6
NSE0_00742a
500 V DC
1 L+ 3 5 L-
2 4 6
NSE0_00743a
600 V DC
The max. direct voltage applies for the circuit breakers VL160 to VL630 with extremely
1)
high switching capacity (L). Otherwise a conversion is necessary in accordance with the
permissible maximum voltage for 3 conducting paths, e.g. VL160X with switching capacity
"N" with factor 250V / 600 V = 0.42.
In the case of 4 conducting paths in series, the 4th pole must be equipped either with a
2)
100% trip unit or no trip unit at all. Moreover, the additional warming of the 4th conducting
path means the maximum operating current must be reduced by 25%, and the trip times of
the thermal overload release can change.
70
= 4000 A setting, the overcurrent trip unit responds at approx. 5200 A ± 20%.
i
N L+ 1 3
N 2 4
500 V DC
N L+ 1 3
N 2 4
NSE0_01538
600 V DC
L+
N 1 3 5
N 2 4 6
600 V DC
for 4-pole circuit breakers
1)
2-pole switching (non-grounded system)
5 L-
If ground faults have been excluded or if every ground
fault is corrected immediately (ground fault monitoring),
6
the maximum permissible direct voltage can be 600 V
NSE0_01537
in both circuits.
2-pole switching (grounded system)
5
L-
The grounded pole should always be assigned to the
single conducting path so that if a short-circuit occurs,
6
2 conducting paths are always connected in series in
the case of 3-pole breakers, or 3 conducting paths in
the case of 4-pole breakers.
1-pole switching (grounded system)
L-
The grounded pole is assigned to the ungrounded
conducting path.
NSE0_00744a
2)
3VL molded-case circuit breakers
System Manual, 03/2009, 110 0110 - 02 DS 01