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| Utilitys revisited https://brainfiller.com/arcflashforum/viewtopic.php?f=2&t=1190 |
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| Author: | BCR_1962 [ Mon Jul 12, 2010 4:40 am ] |
| Post subject: | Utilitys revisited |
After numerous go arounds with a utility reluctant to provide available fault current data, and given our reluctance to storm the place with pitchforks and tourches, we were able to extract the following information: The facility in question is fed from a substation with 3- 40 MVA transformers, "477 conductor" and nominal voltages of 139kV/12.4kV. I am assuming that "477 conductor" means 477MCM and the conductor is almost certainly aluminum. We measured the transmission distance to the substation at 4.5 miles. Now, a quick back of the envelop calculation using a table impedance value for 500MCM AL (wich is what I have handy) and guessing about 8% impedance for the transformer and 1% for the source, I am comming up with about 3800A which seems a fairly reasonable start. My question is, Does anyone know what a reasonable impedance range for a 40MVA transformer might be. Any input would be appreciated. Bob Ragsdale, PE |
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| Author: | stevenal [ Wed Jul 28, 2010 8:26 am ] |
| Post subject: | |
Assuming the primary BIL is 550, ANSI C57.12.10 says 9.0% without load tapchanging and 9.5% with. Note that with three transformers, there are three possible system configurations (source impedances) right there (neglecting all the other possible system changes the utility may make.) |
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| Author: | arcflash71 [ Wed Aug 11, 2010 3:52 pm ] |
| Post subject: | |
I believe you mean C57.12.10 |
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| Author: | stevenal [ Thu Aug 12, 2010 8:05 am ] |
| Post subject: | |
Fixed on edit. Thanks. |
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