Hello, I am new to this forum and seeking help on this calculation I am performing for a Utility. I am using lee method for a >15 kV system on primary overhead at end of the feeder which is approx 13 kM from the station breaker. Currently there are no spur fusing but only MSO on this span which makes the breaker as only clearing device. Therefore a lower fault level and higher clearing time results a very high incident energy on lee method. How should a scenario like this be calculated and what protection measure a utility should practice?

Thanks

Hi,
I am not sure where you are located but if in the USA, it seems like you would fall under OSHA 1910.269 for utilities or utility like installations. Appendix E will give you guidance on performing an arc flash assessment. But most likely you will need to use a program called ArcPro to calculate the incident energy.

EPRI has some empirical equations in their public (free) documents for cases outside IEEE 1584 conditions. Lee is off by a factor of 300% at 15 kV and the error increases with voltage and current. ArcPro is another good option that gives good agreement with experimental results. NESC (IEEE C2) contains a table as well. In short, don't use Lee.

The references given are good. The NESC has tables based on the ArcPro Calculations. The assumption is that this will be a single line to ground fault rather than a 3 phase bolted fault. Some software packages, I am familiar with SKM power tools for windows, will allow you to select and NESC analysis for arc flash.

I agree with the posts above to not use LEE but I would not use SKM if it is single phase as they equate the single phase to 3 phase. If you have 3 phase you can use SKM but single phase would require Arc Pro or similar or NESC....