Technical specifications
6.4 Derating
3VA molded case circuit breakers with UL and IEC certification
Manual, 01/2019, L1V30435333-01
457
6.4.3
Additional correction factors with frequencies other than 50/60 Hz for 3VA5
molded case circuit breakers
The temperature rise in the bimetal is greater at frequencies above 50/60 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 from the value used in 50/60 Hz
applications.
In an application with 400 Hz, this means the following for the example from chapter
Derating of 3VA5 molded case circuit breakers (Page 454) with a 3VA5 molded case circuit
breaker and a desired current I
r
= 90 A:
●
Setting value I
r(400 Hz)
= 90 A · 0.9 = 86 A
Where ambient temperatures differ from the calibration temperature, temperature
compensation as described in chapter Derating of 3VA5 molded case circuit breakers
(Page 454) must be performed.
In addition, a correction factor for setting the magnetic trip unit as a function of frequency
must be applied.
