Technical specifications
6.4 Derating and temperature compensation
3VA molded case circuit breakers with IEC certificate
Manual, 03/2019, A5E03603177010-03
637
6.4.3
Additional correction factors with frequencies other than 50/60 Hz for 3VA1
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 3VA1 molded case circuit breakers (Page 628) with a 3VA1 molded case circuit
breaker when current I
r
= 90 A is required:
●
Setting value I
r(400 Hz)
= 90 A · 0.9 = 81 A
Where ambient temperatures differ from the calibration temperature, temperature
compensation as described in chapter Derating of 3VA1 molded case circuit breakers
(Page 628) must be performed.
In addition, a correction factor for setting the magnetic trip unit as a function of frequency
must be applied.
