Complex Software Guide
Complex electrical modelling software has improved greatly in recent years and the demand is driven not only by traditional electrical design, but by new technologies such as energy efficiency, smart grids, automation, metering, wind power and energy storage as well as increasing complications with mains disturbances. The result is that you will need to specify exactly which functions you will need to undertake a study as each manufacturer packages their products in different ways. This chapter gives guidance and tips on how to approach the purchasing or leasing of the right package for the purpose of arc flash evaluation.
Going to the trouble and expense of procuring complex software will not guarantee safety nor will it guarantee the accuracy of the result when predicting incident energy. Both these outputs depend upon the following factors:
- That the information that is entered into the software package is correct and has been interpreted properly. Otherwise, it is the old adage “garbage in equals garbage out”.
- That you have an understanding of the methods of calculation and have sufficient knowledge to question an unusually high or an unusually low result.
- That the results are applied correctly in the context of standards and regulations that exist within Europe.
- That electrical rules and supporting procedures are in place that will adequately and sufficiently give interpretation and understanding of the results to all workers who may be affected.
In broad terms, in order to carry out an arc flash study, you will need to have a package that is capable of providing a single line diagram, a fault level study, a protection coordination study and finally arc flash evaluation. The following tips can be used to make sure that the correct features are in your shopping list especially from a European perspective.
Software packages are not generally compatible with each other when manufactured by different companies. So, for instance, if a study is being carried out using software from manufacturer A, then all the work that has been carried out in data collection may have to be repeated to model the system in software from Manufacturer B. I have previously highlighted data collection is often a substantial part of the effort required to produce a study so this could be important. Companies sometimes provide data conversion software but from experience, I would want to be convinced that this works effectively before basing any purchasing decision on the availability of such software.
13.2 Single Line Diagram.
Most software developers provide evaluation copies of their software, usually up to one month. The evaluation copy will nearly always have a single line diagram and it is worth a test drive to see just how user friendly this is. The single line diagram is after all, the interface that the user will be dealing with the majority of the time and productivity will be driven by how quickly the single line diagram can be built and how components can be entered and edited.
13.3 Fault level study.
Most software companies will give a choice of fault level calculations standards. There are two main standards that are used to calculate fault levels in an electrical network. There is the ANSI standard that is used throughout the USA and Canada, and then IEC standard which is used predominantly in Europe. The standards use different methodologies and will arrive at different value in certain circumstances. There used to be a school of thought that, because the IEEE 1584 standard was developed in the USA then the ANSI standard of fault current evaluation was the correct one to use in order to arrive at the bolted short circuit current (prospective fault current). However, the arc flash study is only a small part of the overall process. The strength and capability of the equipment being evaluated must also be taken into account and if it is built and rated in accordance with IEC standards, then the IEC methodology must be used to calculate fault duties.
There is a paper which explores the use of both methods for arc flash studies called “Comprehensive Overview and Comparison of ANSI vs. IEC Short Circuit Calculations: Using IEC Short Circuit Results in IEEE 1584 Arc Flash Calculations” IEEE PCIC Conference proceedings, Cincinnati, OH Sept. 2018. (A. Majd, R. Lou, M. Devadass, J. Phillips). In it, there are sample calculations and comparisons between the two methods. Whilst no generalisations can be drawn about the differences, the paper acknowledges that the IEC method can be effectively used for arc calculations.
13.4 Protection coordination study.
In the early days, my data collection efforts did not just consist of discovering site data, but also providing backup to the software developer for missing devices in their libraries. The software libraries for time current characteristics and types of protection were predominantly North American and were limited for IEC devices. This has been broadly overcome, thanks in part to my efforts no doubt, and libraries tend to be much more comprehensive. It is a legitimate question when procuring software to ask about which devices listed and what methods will be used to take account of those devices that are missing. For instance, is there a method of entering time current curve points manually, how does it work and also, what is the response time from the support team for including a missing device?