Arc Flash, Coordination and Short Circuit Study for an Industrial Facility, Bayou Vista, Louisiana (2022)

In 2022 we completed an arc flash, coordination and short circuit study for an industrial facility in Bayou Vista, Louisiana. Client details are confidential.

Branch breakers in one of the panelboards recorded during the walkdown. Every breaker in the model is identified down to its type and rating.

A medium-voltage service

The facility takes one primary utility feed at 34.5 kV into underground vaults, where transformers step it down to the plant voltages. Protection is mostly fuses and circuit breakers. A separate power source supplies the office space in the main building, and a standby generator can carry the plant. Medium-voltage service matters for an arc flash study because the fuses and relays at the top of the system decide how long a fault on the low-voltage side can last.

When the utility data is missing

The available short circuit capacity at the utility connection was not reported to us. Instead of waiting, we estimated the primary short circuit availability from the transformer data with IEC 60076-5, then tested variations of that assumption to make sure the results held. The rest of the system data came from the owner one-lines and from our walkdowns. Where data was incomplete or could not be collected safely, we made bounding and conservative assumptions, and the report states that it is not an as-built record of the facility.

Two operating cases

The system was modeled in ETAP 21.0.1, with cable lengths and sizes, transformers, panels, automatic transfer switches and generators. The arc flash analysis followed NFPA 70E-2018 and IEEE 1584-2018 and was run for two configurations: normal operation on the utility, and the standby generator supplying power. The labels carry the worse of the two. Where incident energy came out above 40 cal/cm², we lowered it as far as the equipment allowed and recommended de-energized work as the first option.

Revision 1 and the system alerts

After the first issue, revision 1 revised the short circuit results and settings, and every appendix changed. It also added a list of critical changes the system required, and a new appendix of system alerts flagged equipment that needed attention. The report asks that each breaker be checked against the settings document, because a breaker set differently from the study changes its clearing time and the incident energy with it.

Arc flash studies in Louisiana

What a study includes is described on the page for our arc flash study services. Other work in the state is listed on our page for Louisiana.