Siemens 3VA1 100 A Manual page 137

Features specific to 400 Hz supplies
The thermal overload release of the 3VA1 molded case circuit breaker comprises a bimetal
through which current flows, causing temperature rise. With currents at 400 Hz frequency,
the temperature rise in the bimetal is higher than at 50 Hz. This is due to eddy-current losses
and the reduction in the available conductor cross section as a result of the skin effect. The
rated operational current must therefore be reduced by 10 % of the value used in 50/60 Hz
applications.
Furthermore, a correction factor must be applied to the magnetic trip unit.
Example:
3VA1 160A, TM240 ATAM:
● Reduction by 10%:
Maximum permissible rated operational current for 400 Hz applications =
160 A x 0.9 = 144 A
● Correction factor 0.7:
If the switching device is to trip instantaneously in response to an overcurrent of 1200 A,
the parameter I
0.7 = 840 A.
For further information on trip units and details about the setting parameters, please refer to
chapter Line protection applications of 3VA molded case circuit breakers (Page 105).
It is not possible to use electronic trip units for this application.
See also
Temperature compensation with thermal-magnetic trip units of the TM 2-series (Page 491)
3VA molded case circuit breakers
Manual, 04/2015, A5E03603177010-02
3.4 400 Hz network applications of 3VA molded case circuit breakers
for instantaneous short-circuit protection (I) must be set to I
i
Applications
= 1200 A x
i
137