recently at work I was asked to siza a transformer for a 200Amp 575 Volt Machine. At our facility we have 480 volt wye substations, so I needed a step up transformer. I began by rating my load a t 125% which would be 250Amps at 575Volts. According to a chart I have at work from an electrical pal book, the next available KVA size for this would be a 300KVA transformer which shows an available 288 Amps @ 600VAC. According to the chart, a 300KVA transformer would pull 388Amps on the 480 Volt Primary. Besides using this chart, how can I properly size a three phase transformer given the volts and amps of a given load. I know that power in is equal to power out so given the secondary VA I can find the primary VA. also how does Delta and Wye figure into the equasion?
transformer sizing
- Thread starter rwooten
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Your machine requires 200 x 575 x 1.73 = 198950 va/1000=200 kva.
That is the minimum size for the transformer. You have some loss in the transformer so you will need to increase it. The next size is 300 kva.
You can order a 300 kva transformer rated for your primary voltage.
Check with the mfg and see if you can get 575 volts on the secondary. You may have to settle for 600 volts. The machine should have a rating
for max voltage. Check and see if 600 volts is within the range.
What type of machine is it? If it is a motor you will have to be sure that the starting amps will not trip the OC device.
That is the minimum size for the transformer. You have some loss in the transformer so you will need to increase it. The next size is 300 kva.
You can order a 300 kva transformer rated for your primary voltage.
Check with the mfg and see if you can get 575 volts on the secondary. You may have to settle for 600 volts. The machine should have a rating
for max voltage. Check and see if 600 volts is within the range.
What type of machine is it? If it is a motor you will have to be sure that the starting amps will not trip the OC device.
Thanks for the reply. I have yet to see the machine, I was told that the FLA of the machine was 200A @ 575V. It has several machining heads, motors probably not much larger than 5HP. There is also a coating applicator and an oven to bake the application on. I usually size a transformer at 125% of full load so I used 250A x 575 x 1.732 = 248975 va/1000 =248.9KVA, so I came up with the same thing that the next standard transformer size being 300 KVA. I will be powering the 300KVA transformer from a 400 Amp 480V panel, so I should be fine on the secondary considering I will have 300 available amps when the fla is only 200A. I feel comfortable knowing that I have a 100A cushion in my specification. It has been a while since college and I was just a little unsure the ins and out of sizing transformers. Mike holts web site has been very helpful in the use of the code forum and the other sections of the web site have been helpful also. Thanks again
winnie
Senior Member
- Location
- Springfield, MA, USA
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- Electric motor research
Buck/Boost for this application?
Buck/Boost for this application?
Question: is this an application that could be supplied with a buck/boost? On the theory side you could use 40KVA of transformers to supply 200KVA of 575V from a 480V source, but I don't know the implications for code compliance, OC protection, or power quality for these applications.
-Jon
Buck/Boost for this application?
Question: is this an application that could be supplied with a buck/boost? On the theory side you could use 40KVA of transformers to supply 200KVA of 575V from a 480V source, but I don't know the implications for code compliance, OC protection, or power quality for these applications.
-Jon
- Status