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| Utility Transformer Fusing https://brainfiller.com/arcflashforum/viewtopic.php?f=4&t=1922 |
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| Author: | ronlow00 [ Fri Nov 18, 2011 9:08 am ] |
| Post subject: | Utility Transformer Fusing |
I am currently working on a project for a 480Y/277V system. The electric utility has given me their information. Included in this information is the type of fuses they use at their transformer. Now if I include the utility transformer fusing information in my study, the Arc Fault hazard is greatly reduced in the system I'm studying. However, the utility warns that their information and the fusing may change without notice. So, what is everyone's thoughts on including the utility transformer fusing in the system study. I believe since it is part of the system it should be included, but I question it a bit since it can change without notice. any thoughts? |
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| Author: | JoeB [ Fri Nov 18, 2011 9:33 am ] |
| Post subject: | |
Just a few thoughts. It would be difficult to explain why the incident energy is large if you do not use the utility fuse data. If we are overly concerned about the possiblity of changes from the utility, what if a maintenance person changes settings internal to the customer's power system - similar problem to the utility fuse change concern. The utility short circuit data can also change without notice, yet we continue to use this data. It really comes down to reviewing the study periodically to make sure there are no significant changes (NFPA 70E requires this). Just my thoughts. I'm sure others may have good opinions also. |
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| Author: | richxtlc [ Fri Nov 18, 2011 11:53 am ] |
| Post subject: | |
That is one of the reasons we periodically evaluate the incident energy, either changes to the electrical system, or changes for the utility. you can ask them, periodically if there have been any significant changes in the available fault current or changes in the class or type of OCPD used on your incoming service. The impedance of the utility can change when they take a feeder or transformer out-of-service at the facility servicing your customer. That is why you take their available fault current and give it a percentage up and down to see what happens if the available fault current increases or decreases from the value they gave you. |
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| Author: | ronlow00 [ Fri Nov 18, 2011 12:45 pm ] |
| Post subject: | |
I agree with both of you, and it is good to hear that others are on the same page. Thanks for the input. |
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| Author: | jghrist [ Mon Nov 21, 2011 11:21 am ] |
| Post subject: | |
ronlow00 wrote: I am currently working on a project for a 480Y/277V system. The electric utility has given me their information. Included in this information is the type of fuses they use at their transformer. Now if I include the utility transformer fusing information in my study, the Arc Fault hazard is greatly reduced in the system I'm studying. However, the utility warns that their information and the fusing may change without notice. So, what is everyone's thoughts on including the utility transformer fusing in the system study. I believe since it is part of the system it should be included, but I question it a bit since it can change without notice. any thoughts?
If you didn't include the utility fusing information, what clears a fault on the source side of your first OCPD? I would say use the information on the existing protection. As others have said, periodically review the data. Also, if you observe the utility replacing their equipment, ask for new information. |
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