Siemens SENTRON 3VL System Manual page 76

Application planning
6.6 Use in the motor protection area
Phase failure sensitivity
The "phase failure sensitivity" function is also integrated into the SENTRON VL circuit
breakers for motor protection. This ensures that the motor is reliably protected against
overheating if a phase interruption or a large fluctuation occurs.
The specified operational current IR is automatically reduced to 80% of the set value if the
r.m.s. values of the operational currents in the three phases differ by more than 50%.
Deviations of more than 50% mean the value of the current in the least loaded phase drops
to a level below 50% of the maximum loaded phase.
10000
5000
2000
1000
Figure 6-3
Tripping characteristic curve for circuit breakers with electronic overcurrent trip unit.
I 100 kA maximum at 415 V
cu
Figure 6-4
① Without "thermal memory"
② with "thermal memory"
76
1.25x 1,5 2 3 4 5 6
500
200
100
50
20
10
TC=30
5
TC=20
TC=15
2
TC=10
TC=5
1
,5
,2
,1
,05
,02
,01
,005
,002
,001
1 2 4 6 10 20 40
ETU with trip classes 5, 10, 15, 20, 30
Response time of the trip unit after overload release
NSK-1134b
8 10 11x
60 100 200 400 2000
I
A x
R
3VL molded-case circuit breakers
System Manual, 03/2009, 110 0110 - 02 DS 01