The IEEE Standard 1584 – IEEE Guide for Performing Arc-Flash Hazard Calculations provides a method for calculating arc flash hazard for electrical distribution systems. The first edition of the standard was released in 2002 using an empirically derived model based on arc flash measurements performed in a laboratory. When further research yielded results differing from the energy predicted by the model, a revised standard was published in 2018. The new edition features more variables such as switchgear design.
The standard provides the following method for calculation:
The equations have a limited range of validity for current and voltage although most industrial systems are within these limits.
Details about the electrical distribution system are required to accurately calculate the hazard level. The following lists the information typically required:
Typically, an onsite data collection effort is required to verify drawings are accurate. This is especially a concern for older installations.
When the electrical distribution system is operated in different modes, scenarios can be created that simulate the entire range of operating parameters. This ensures that the worst-case hazard is found. As an example, the following scenarios may be created:
A calculation needs to be performed for all applicable scenarios and evaluation should be based on the worst-case result. Which scenario yields the worst-case result is determined for each location separately.
The results of the short-circuit evaluation can be used for checking if switchgear and protective devices are adequately rated against short-circuit currents.
During data collection the short-circuit withstand of all switchgear and protective devices is gathered and compared to the maximum calculated short-circuit current. When current-limiting devices are present (such as fuses or molded-case circuit breakers) their limiting effect will be included as far as documentation is available.
The following parameters are evaluated:
Any issues with inadequate rating of equipment are immediately reported, as they can create unsafe working conditions.
Overcurrent devices that are modelled should be checked for miscoordination for overload and short-circuit currents. When during an overcurrent more than one device trips, these devices are said to not provide full coordination, and this may present operational issues (although not necessarily safety related). In this case alternative protection settings can be explored that do provide improved or full coordination.
A report should include a list of locations where full coordination is not available. Alternative protection settings can be presented with their limits, as this is usually a compromise between operational stability, safety and cost. A setting evaluation will consider the following information:
Using the result of the short-circuit evaluation and the protection device coordination studies, the arc flash incident energy and the associated boundary can be calculated according to the equations in IEEE Standard 1584. A report should provide the calculation results, source data and any approximations or analytical variables used.