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 Post subject: Label Low Voltage Transformers?
PostPosted: Tue May 03, 2011 7:50 am 
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Joined: Thu Oct 08, 2009 12:16 pm
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Location: St. Paul, MN
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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PostPosted: Tue May 03, 2011 8:20 am 
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Location: Wisconsin
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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PostPosted: Tue May 03, 2011 8:36 am 
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Location: St. Paul, MN
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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PostPosted: Tue May 03, 2011 9:25 am 
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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/cm┬▓ then it needs a label more than Cat 0.


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PostPosted: Tue May 03, 2011 9:39 am 
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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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