The 65th Annual IEEE-PCIC Conference will be held this year in Cincinnati, Ohio on September 24-26.
This year I will have both my “IEEE hat” and “IEC hat” on and join a couple of colleagues in presenting a technical paper comparing the use of ANSI vs. IEC short circuit calculations as part of an arc flash study. The official title is: “Comprehensive Overview and Comparison of ANSI vs. IEC Short Circuit Calculations: Using IEC Short Circuit Results in IEEE 1584 Arc Flash Calculations” Continue reading →
Short Circuit Calculations – Transformer and Source Impedance
An infinite bus short circuit calculation can be used to determine the maximum short circuit current on the secondary side of a transformer using only transformer nameplate data. This is a good (and simple) method for determining the worst case MAXIMUM short circuit current through the transformer since it ignores the source/utility impedance. Ignoring the source impedance means it is assumed to be zero and voltage divided by zero is infinite, hence the often-used term “infinite bus” or “infinite source”.
National Electrical Code 110.9 Interrupting Ratings states that:
Equipment intended to interrupt current at fault levels shall have an interrupting rating at nominal circuit voltage at least equal to the current that is available at the line terminals of the equipment.
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To comply with this requirement, a short circuit studies is typically performed to determine the available fault current for comparison to the protective devices interrupting rating. The results of a short circuit study are also a critical component for other studies such as an arc flash study. Requesting the available short-circuit data from the electric utility company should be one of the first tasks in performing the study. This information is very important because it defines the magnitude of current that could flow from the utility and is used as a starting point for arc flash calculations.
In addition to requesting this data for normal operating conditions, for an arc flash study the request should also include minimum short-circuit current conditions, if available. The minimum condition could be for a utility transformer or transmission line out of service or similar scenario. The minimum value can then be used to determine if the lower current could result in a protective device operating more slowly, which may increase the total incident energy during an arc flash.
Having been in charge of the Short Circuit Studies group for a very large electric utility company in a past life, the accuracy of the Continue reading →
Hi. I currently work as an Engineer in the energy management field. I would like to branch off in to doing Arc Flash, Short Circuit and Coordination Studies. How would I go about doing this. I have been exposed to these reports but have never done them before. Would any of you happen to have any training material on how to get started? From what I’ve read I should learn how to do these reports manually then look in to getting software to aid with the reports. Not sure if it matters or not but I’m located in Canada. Thanks. READ MORE
I recently came across a previous study that was completed for a facility that assumed a specific type of conduit [non-metallic/magnetic; PVC] vs what was actually installed [Rigid Meal Conduit], in digging into this deeper and looking at some of the short circuit calculations information available to me it appears that in the calculation they type of conduit [magnetic vs non-magnetic] can play a role in the amount of available fault current. When doing some quick simplistic calculations it appears that the conduit material does play a role and in larger systems could make a difference. I did some digging in my software’s reference material and some other material but could not find adequate explanation / technical data.
I was hoping someone could share or point me to some additional resources on how conduit material affects available fault current? It appears there are different constants for conductors based on the type of installation [conduit type for systems of .208-13.2kV] also what if you have conductors installed in tray [3-1/C cables] does the spacing and configuration of how the cables are installed come into play and where could I find some information on this. Thanks in advance. READ MORE.
About Jim Phillips, P.E.:Electrical Power and Arc Flash Training Programs – For over 30 years, Jim Phillips has been helping tens of thousands of people around the world, understand electrical power system design, analysis, arc flash and electrical safety.Jim is Vice Chair of IEEE 1584 and International Chairman of IEC TC78 Live Working. He has developed a reputation for being one of the best trainers in the electric power industry,Learn More.
It goes up, it goes down, sometimes it is thought to be infinite (although it really isn’t!) and other times it seems impossible to find. “It” refers to the available short circuit current from the electric utility which is one of the more important pieces of information for an arc flash hazard calculation study. Used to help define the severity of an arc flash hazard, it represents the magnitude of current that could f low from the electric utility during a short circuit. Continue reading →
One of the first steps in performing an arc flash calculation study is to request short-circuit data from the electric utility company. This kind of request is pretty routine, and utilities have been providing this type of data for short-circuit studies for years. The problem is the data used for a short-circuit study may not be suitable for an arc flash study. Continue reading →
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