Circuit Breakers and VFDs

[dasarmin]

Generally, Semiconductor Fuses (high speed) are used to protect VFDs, but what type Circuit Breaker would provide the same protection. Thermomagnetic or Electronic Trip CBs are two to consider. Arc Flash standards also need to be met.

 

[petersonra]

Generally, Semiconductor Fuses (high speed) are used to protect VFDs,

Not so much anymore. Most VFD manufacturers do not recommend high speed fuses these days.

but what type Circuit Breaker would provide the same protection.

I guess it depends on what protection you think is needed. i'd be inclined to follow the manufacturer's instructions. they are usually pretty explicit about what OC and short circuit current protection should be used.

Thermomagnetic or Electronic Trip CBs are two to consider.

I am not sure what other kind of circuit breaker there is that would be appropriate for this type of circuit.

Arc Flash standards also need to be met.

Meaning what? There is no such thing as a standard arc flash.

Is there a question in there somewhere?

 

[jim dungar]

Realistically there is no fuse or circuit breaker that can protect the electronics from failing. They can only minimized the amount of damage. External protective devices are there to protect the facility and the power grid from the equipment.

 

[Jraef]

I agree with the other assessments, neither fuse nor CB is going to prevent VFD damage under all conditions. High speed semiconductor fuses might protect against a few more conditions than any circuit breaker, but the bottom line is often that the hassle and extra down time of having to replace them under nuisance clearing situations probably nullifies any gain.

As to which circuit breaker, it makes no difference between the available choices from that standpoint, the best and fastest CB is way too slow to do more than prevent a fire. The choice to go with an ETCB would be based on coordination with other breakers and OCPDs, not the down stream load. So from that perspective, a TMCB is just as good if you are not the one making coordination decisions for the entire distribution system, but an ETCB does provide the flexibility for you or someone else who may want to do that later.