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 Post subject: Unknown transformer data
PostPosted: Wed Oct 08, 2014 7:39 am 
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Hello all,

I am starting the process of performing an arc flash calculation, and as Jim has stated, data collection is very labor intensive. Basically, I have a pole mount transformer which is upstream and owned by my facility, and it would take labor and maintenance personnel with a crane to obtain the faceplate data. I can easily obtain all the data downstream from this transformer. Are there any good values to use for "worst case" scenario? I.e. using an infinite buss calculation with minimal impedance in the conductors after the secondary? Could I use a %Z value that is at the absolute lowest of a practical range? All of this would be to obtain the max available fault current, and I would then use software to model all clearing devices to cover faults with less current and more duration.

Or... is pushing to try to view faceplace data on the transformer (if it exists) the only way to go?

Thanks!


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 Post subject: Re: Unknown transformer data
PostPosted: Wed Oct 08, 2014 8:35 am 
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Joined: Mon Sep 17, 2007 5:00 pm
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Location: Scottsdale, Arizona
Here is a trick that was sometimes successful. Binoculars or a camera with a good zoom lens. Depends on what condition the name plate is in and whether it is visible or facing the pole too. Good luck.


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 Post subject: Re: Unknown transformer data
PostPosted: Wed Oct 08, 2014 11:20 am 
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Hi,
As a designer, we do calculate kva load and size a required transformer. A little too small can cause voltage drop and an oversize is not cost effective. Therefore, transformer is an important piece of equipment in your facility and you should ruffle through your office files first to find its detail. For sure somebody will definitely know about it. For your information, obtaining maximum short circuit value by using lowest transformer impedance will not always result in worst case scenario. What about if the short circuit value is high enough to open your protective device in fractional ms? Then you will have much lower incident energy. On the other hand, even if you have lower short circuit value, and your protection device takes longer to open, then the accumulative incident energy will be much higher. If I were you, I would find who the utility company is, and shoot and RFI to get the utility information on the primary side of your transformer. In the mean time, dig the transformer information and model the plant. Then you can create multiple scenarios and study the case in depth. I wouldn't suggest something like using crane to obtain transformer information. That is not safe. Remember? how a firefighter got electrocuted in ice bucket challenge accident few weeks ago.


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 Post subject: Re: Unknown transformer data
PostPosted: Wed Oct 08, 2014 11:40 am 
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Joined: Wed Oct 08, 2014 7:32 am
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Jim, thanks for the idea, binoculars ha, seems too simple for an engineer to think of, but I will try it!

And thanks for your reply Namgay, I would consider smaller amounts of short circuit current in my calculations, but this would require analysis at all current levels and time durations with the coordinated protective devices. Therefore, I would need to know the max short circuit current and use all short circuit values below the max. This was my train of thought, not calculating arc flash based on the max short circuit current, but calculating based on all ranges of short circuit current. Good point with the safety of using a crane! The risk of reading the nameplate could be a greater safety concern than the actual arc flash itself, so I will keep this in mind and keep digging to find the data.


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 Post subject: Re: Unknown transformer data
PostPosted: Wed Oct 08, 2014 1:32 pm 
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eckert86 wrote:
Hello all,

I am starting the process of performing an arc flash calculation, and as Jim has stated, data collection is very labor intensive. Basically, I have a pole mount transformer which is upstream and owned by my facility, and it would take labor and maintenance personnel with a crane to obtain the faceplate data. I can easily obtain all the data downstream from this transformer. Are there any good values to use for "worst case" scenario? I.e. using an infinite buss calculation with minimal impedance in the conductors after the secondary? Could I use a %Z value that is at the absolute lowest of a practical range? All of this would be to obtain the max available fault current, and I would then use software to model all clearing devices to cover faults with less current and more duration.

Or... is pushing to try to view faceplace data on the transformer (if it exists) the only way to go?

Thanks!


Just for the fun of it, consider using gyro drone with HD camera to read the transformer nameplate. A friend of mine has recently purchased one on ebay for USD60 and he can't now stop talking about how much fun he has playing with the toy.

I'm pretty positive that if you make a picture of the transformer and post it on one of the electrical forums, someone will help you to identify its make and/or size. Pole mount transformers KVA ratings range from 16 kVA to 100kVA. You can use standard X/R and %Z data for arc flash assessment if manufacturer X/R and %Z information is not available.


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 Post subject: Re: Unknown transformer data
PostPosted: Thu Oct 09, 2014 5:29 am 
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Location: Rutland, VT
You should contact the utility to obtain the available fault current and X/R as that is what you should use for arc flash hazard analysis. Even though the txf is owned by you the utility will have protection on their side of the transformer where the demarcation point is, typically where the primary metering system is.

Another item I noticed is that you mention pole mounted transformer in the singular tense, not plural. Is it one single phase pole mounted transformer or a cluster of 3?

Another item to look at is the size of your main breaker/fuse. That could give an indication of the size of the txf.


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 Post subject: Re: Unknown transformer data
PostPosted: Mon Oct 20, 2014 11:06 am 
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To add what has been already posted: I use a digital camera with telephoto lens. Normally with the camera set to shutter speed priority and set as fast as possible with the camera lens max aperture setting (so camera vibration/shake is minimal especially when hand held) and aperture set to auto usually works. Handheld photos usually work, but using a tripod is best. Those times when the lens isn't adequate to discriminate the text (or some text) on the name plate, putting the digital file on a computer, then digitally zoom in. If none of this works because the text is too small and/or the transformer is too far away, using a spotting scope of the type used on gun ranges works incredibly well, but must be on a good tripod. Good spotting scopes are not at all cheap, but very useful. Linemen may have one.


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