Effects of Harmonics in Circuit Breakers

[niallnz]

I am installing new VSD's and motors on a crane that was originally built in 1965. I have been able to estimate that under the worst case conditions the current THD will be approximatly 35% (which will be virtually un noticable to the rest of the plant). However we are retaining some of the existing 400V electrical distribution equipement, including the 300A main circuit breaker. My client wants to know if the CB will be affected by the harmonics, (5th about 29%, 7th 14% etc). Any suggestions or comments would be appreciated.

 

[JBD]

Thermal-magnetic circuit breakers are true RMS devices and are not affected by harmonics. These types of breakers respond to the total heat and magnetic force generated by all current flowing through them.