Arc Flash calculation - Why is breaker opening time zero?

[Magic Gorge]

When doing arc flash hazard analysis, there is a report option in SKM to show the "breaker opening time/tolerance" and after I run the calculation (480V system), this value = 0 seconds for all locations. Not all of the locations hit the max trip time of 2 seconds, so some breaker must be operating, what is the "opening time" telling me? I do not see anywhere that this field can be edited. There are no relays or fuses, just breakers in this protection scheme.

 

[wbdvt]

Not sure about SKM but in EasyPower the opening time is for HV breakers or opening device after the relay trips. This column will be blank for a fuse or LV breaker as the trip time for these devices already include the opening time so the column will be blank.

It may be the same for SKM. Did you look in the Help files?

 

[Magic Gorge]

Yes, the help files hinted that the opening time is included in the total clearing time, but the trip curves have an associated opening time for all the trip levels when I look at the device library, so I'd assumed it would show up on the table. So, is it accurate to say that the opening time may not be zero for the lv breakers, but it is included in the total clearing time?

 

[mayanees]

if you're current with your SKM maintenance fee you can get all the help you need from them.
That being said, if your ocpd is a breaker time-current band that represents the operation of the breaker, you time out when the arcing fault has passed through the clearing point of the band which will agree with the SKM 1584 report. If your ocpd is a line that's representing a relay, then you need to add the amount of time it takes for the operating mechanism to operate, i.e. a 3- or 5-cycle breaker.

 

[jlee405]

Yes, the help files hinted that the opening time is included in the total clearing time, but the trip curves have an associated opening time for all the trip levels when I look at the device library, so I'd assumed it would show up on the table. So, is it accurate to say that the opening time may not be zero for the lv breakers, but it is included in the total clearing time?

That is how I understand it. The LV breaker time current curve includes that, which is why it is thick. Relays do not (skinny line), since opening time can be dependent on the processing times of the relays, the time it takes to receive the signal from the CT, which can vary with wiring lengths. Which is why we need to look at coordination time intervals for relays. Check out SKM's FAQs.

 

[smoothops10]

Assuming you installed in the default directory go to C:\PTW32\Doc and open Reference-CAPTOR.pdf. Will give you all the information in you need including creating your own TCC for devices not in the standard library.