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 Post subject: Working distance for Transformer
PostPosted: Tue Dec 04, 2012 1:49 pm 
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I can't find working distance from IEEE 1584 for the transformer. How do you decide this if you need to do AF study for a transformer?


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PostPosted: Wed Dec 05, 2012 10:25 am 
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You are correct, that one is not in there. I would probably use the smallest of the distances listed - 18 inches unless a hot stick is involved.

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PostPosted: Fri Dec 07, 2012 9:49 am 
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That would be an interesting label if both primary and secondary winding connections are in the same area (i.e. dry type). One voltage and Ei for the primary and a different Ei and voltage for the secondary and two different boundaries. I'd be interested in seeing the label.


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PostPosted: Sat Dec 08, 2012 8:09 am 
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that's how you label them unless it is large enough to have two cabinets. we use a split voltage such as 4160/480 and worst case incident energy which is usually very high because of the secondary side.


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PostPosted: Mon Dec 10, 2012 7:48 am 
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Our labels on dry types transformers only have one label that is for the worst case (either primary or secondary side).


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PostPosted: Mon Dec 10, 2012 8:18 am 
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I agree with eelssu2001. It is important to not have labels that might be confusing. Using a single label, with the worst case, is the approach to use.


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PostPosted: Mon Dec 17, 2012 7:07 am 
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Why is energized work been performed on the primary or secondary of a power transformer?


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PostPosted: Mon Dec 17, 2012 1:17 pm 
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Say you are taking an oil sample while the transformer is energized. Thats one reason I can think of.


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PostPosted: Tue Dec 18, 2012 9:26 am 
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Terry Becker wrote:
Why is energized work been performed on the primary or secondary of a power transformer?

As Juan Mentioned, Oil Samples. Also for utility style padmounts, verfication of Oil Level, tank pressure require access to the compartments. For those transformers where loop switches are an integral part of the transformer, any system switching/ loop reconfiguration requires opending up the MV compartment, which first requires opending the secondary compartment. Partial discharge testing, IR scanning, also come to mind.


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PostPosted: Wed Jan 16, 2013 6:08 pm 
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I think we need to remember that for taking a DGA sample, for example, one is not interacting with the equipment in a manner that could cause an electrical fault. Same thing with IR, PD, etc.

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PostPosted: Fri Jan 18, 2013 6:00 am 
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wbd wrote:
I think we need to remember that for taking a DGA sample, for example, one is not interacting with the equipment in a manner that could cause an electrical fault. Same thing with IR, PD, etc.


Infrared scanning I can understand because it’s not as invasive and a greater distance can be maintained; the only real interaction for this task is opening the enclosure door.

However, taking an oil sample requires workingwithin both the Restricted Approach Boundary and the Arc Flash Boundary (unless you have external access). The valve used for obtaining samples is typically located inside the secondary portion of the transformer enclosure towards the bottom. Often the arc flash analysis will show a large incident energy available at this location because this area is only protected by the transformer's primary device. You would not consider this work to require shock and arc flash PPE?


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PostPosted: Fri Jan 18, 2013 6:33 pm 
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Depends on the transformer. Padmount distribution units are typically in public spaces so the valve is often inside an area which is exposed (though I special order them with the pipe routed outside). Substation style transformers have ducts and the sample port is outside.


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PostPosted: Sat Jan 19, 2013 8:17 am 
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True, my fault as my point of view is from a utility on this. I was thinking of substation power transformers where the sampling valve is located off of the main drain valve at the bottom of the transformer. One is well away from any exposed conductors.

A smaller padmount txf would be different. The valve is located inside the access doors and typically the high side would have load break elbows which are insulated and the low side is typically bare spade pad connectors. There you are most likely in the limited approach distance for that voltage.

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PostPosted: Fri Feb 22, 2013 9:05 am 
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Sorry I posted this somewhere else....
If I were to do an arc flash calculation for an 13.8kV/600V/347V Padmounted Enclosed Transformer, would the IEEE 1584 apply, as they are for switchgear, MCCs and panelboards, and transformers are not explicitly included?
Now, if we do proceed in applying the IEEE 1584, would it then be OK to assume:
XFMR Primary 13.8kV: 152mm Bus Gap, x-factor of 0.973, working distance of 910mm (treating as 15kV SWGR)??
XFMR Secondary 600V: 32mm Bus Gap; x-factor of 1.473, working distance of 610mm (treating as LV SWGR)??
And then finding the worst case IE (almost always the secondary of the padmounted transformer), and applying just one label? Usually the PPE Category of the primary is 1 or 2; and secondary is 3 or 4 or dangerous, anyways.


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PostPosted: Sat Feb 23, 2013 5:32 pm 
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The exponents take into account equipment configuration. As the termination compartments are quite large even in dead front it will be most similar to a medium voltage switchgear. The distances should probably be measured.


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