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| Label Low Voltage Transformers? https://brainfiller.com/arcflashforum/viewtopic.php?f=2&t=1696 |
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| Author: | ronlow00 [ Tue May 03, 2011 7:50 am ] |
| Post subject: | Label Low Voltage Transformers? |
I have a question. In our industry we work a lot with dry type transformers with a 480V primary and a 208 or 240V secondary. Typically these transformers are under 125kVA. When I run calcs, typically the secondary side has a higher hazard than the primary. So my questions are: 1) Do you typically apply a label to the transformer? 2) If yes to #1, does the label represent the primary or secondary side hazard, even though the secondary is 240V or less? |
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| Author: | JBD [ Tue May 03, 2011 8:20 am ] |
| Post subject: | |
Think about how a small transformer is built, the terminals are effectively: LV-HV-LV-HV-LV-HV-LV. It is almost impossible to have a L-L fault on the secondary that does not create a L-L fault on the primary. However, when a customer requires a label on a transformer we will use the worst case AFIE and the highest voltage, irrespective of if it is on the primary or secondary. |
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| Author: | ronlow00 [ Tue May 03, 2011 8:36 am ] |
| Post subject: | |
Thanks for the replay, so is it industry standard to place a lablel on the transformer? Perhaps I have something set wrong with in my EasyPower, but typically the higher voltage has a lower AFIE, so when you say worst case and highest voltage are you refereing to two lables (typically the 480V side is Class 0 and the secondary side comes up as Class 1 or 2) |
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| Author: | jghrist [ Tue May 03, 2011 9:25 am ] |
| Post subject: | |
If it is 208 volt and under 125 kVA, then it falls under Exception No. 1 to 130.3 and analysis is not required for the secondary. If the primary is higher than 1.2 cal/cm² then it needs a label more than Cat 0. |
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| Author: | JBD [ Tue May 03, 2011 9:39 am ] |
| Post subject: | |
ronlow00 wrote: Thanks for the replay, so is it industry standard to place a lablel on the transformer?
Perhaps I have something set wrong with in my EasyPower, but typically the higher voltage has a lower AFIE, so when you say worst case and highest voltage are you refereing to two lables (typically the 480V side is Class 0 and the secondary side comes up as Class 1 or 2) Your program is probably providing correct results. It is extremely unlikely that a secondary fault will cause the primary devices to operate very fast, resulting in a very long clearing time. We use a single custom label, listing the highest voltage (in most cases the primary) and the highest PPE category (in most cases on the secondary). In general, I am not a believer in multiple labels on a single device. |
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