480v to 575v Transformers

Hello,
We recently acquired a machine that requires a 575 volt supply for three large 3 phase AC motors. Combined the motors draw about 340 FLA. We were
told the machine was 480 volt, so when the thing came in we were rather surprised to find it wasn't. Now I need to find a transformer solution ASAP, unfortunately I've been quoted long lead times. Can anybody recommend suppliers who might have such a transformer "on the shelf"? Seems like I would need at least a 250Kva 480v-575v transformer, or a boost arrangement to achieve the same thing. This machine needs to be operational as quickly as possible and I don't have 4-5 weeks to wait for delivery.
Rewinding the motors is an option I would rather avoid.
uray
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It may be possible with three 1 50kVA drytype transformers 240 X 480120/240-volts with 2-2 1/2% FCAN & 4-2 1/2% FCBN taps in "nested delta" autotransformer confiiguration [H4-X1/X3 on each] Works out to ~550V - on normal taps... adjust at startup.
--s falke
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We had the same problem several years ago on a module for the North Slope in Alaska. The system was designed for 575 volts and of course we use 480 volts instead. A lot of the drill rigs are of Canadian Design and this module was a drilling mud recycling plant that mounted onto the end of a drill rig at North Star Island near Prudhoe Bay. We searched high and low for a transformer and ended up using a generator that produced 575 volts for temporary power to test the module. Once it got to the drill rig the 575 volts was readily available. Seems like generators are more common than the 575 volt transformers. Good luck!
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In my steelmaking days the Melt Shop manager was forever buying weird things that we had to make work on 575 ( either 380 V if he'd just been to Europe or 480 V if he'd been to the States). At one time I had the Hammond autotransformer catalog numbers memorized - check for a Hammond dealer near you. An autotransformer will be lighter, smaller, and cheaper - with luck it will also be faster delivery than a two-winding transformer.
340 A at 575 V is closer to 340 KVA - 1 KVA per amp. Best to oversize the transformer if you can, especially if the motors start together.
Bill

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| We recently acquired a machine that requires a 575 volt supply for three | large 3 phase AC motors. Combined the motors draw about 340 FLA. We were | told the machine was 480 volt, so when the thing came in we were rather | surprised to find it wasn't. Now I need to find a transformer solution | ASAP, unfortunately I've been quoted long lead times. Can anybody recommend | suppliers who might have such a transformer "on the shelf"? Seems like I | would need at least a 250Kva 480v-575v transformer, or a boost arrangement | to achieve the same thing. This machine needs to be operational as quickly | as possible and I don't have 4-5 weeks to wait for delivery.
Motors are usually quoted as being for voltages like 115, 230, 460, and 575. But the nominal voltages are 120, 240, 480, and 600. Had you gotten the correct voltage, it would have been labeled as for 460 and you would run it on 480. If you were in Canada, you get the 575 version and run it on 600 which is commonly available in Canada.
So ultimately what you need is 600 volts.
Does the machine require WYE (needs the neutral) or will it work on DELTA?
There are several options.
1.
A 480 -> 240x120 single phase transformer probably could be wired up as a boost transformer. The secondary would be wired for 120 by paralleling the two secondary windings. Then that winding would be put in series with the primary.
Draw an equilateral triangle on a piece of paper. Now draw extensions on each of the 3 lines in the clockwise direction with a length of 25% more. The ends of those extensions will be the boosted delta.
I don't know the ratings you'd need. I've never done the capacity calculations for buck-boost transformers.
2.
If your power is coming in the form of 480Y/277, you could also boost the 277 to 346 to get 600Y/346. Transformers are not made for these voltage combinations, but you could use the 480 -> 120 for this in a derated form to make 277 -> 69, and turn that into a 277 -> 346 boost. This would simply extend the WYE hot legs.
3.
You could build a delta-delta isolation transformer bank using *SIX* single phase 600 -> 240x120 transformers running backwards. Wire the transformers for 600 -> 240 (secondary in series). Now I will refer to it as a 240 -> 600 volt transformer. Take TWO of them and wire the 240 volt primaries in series and the 600 volt secondaries in parallel. Now two of them make a 480 -> 600 volt transformer set. Three such sets lets you make a closed delta. I'm guessing this can be done with 50 kVA transformers (about $3300 at full list price, which should be half that if you shop around, and maybe even less if you find someone who likes the idea of selling six of them at once).
Since you need them fast, call Canadian suppliers as these would generally only be a stock item in 600 volt land (600 volts is rare in US).
Are you going to get the vender of the machine that flubbed the order to spring for the cost of these transformers?
Be sure a competent electrician wires these, and properly tests the voltages before closing the delta.
--
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| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
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On 30 Apr 2004 05:56:49 GMT snipped-for-privacy@ipal.net wrote:
| | | We recently acquired a machine that requires a 575 volt supply for three | | large 3 phase AC motors. Combined the motors draw about 340 FLA. We were | | told the machine was 480 volt, so when the thing came in we were rather | | surprised to find it wasn't. Now I need to find a transformer solution | | ASAP, unfortunately I've been quoted long lead times. Can anybody recommend | | suppliers who might have such a transformer "on the shelf"? Seems like I | | would need at least a 250Kva 480v-575v transformer, or a boost arrangement | | to achieve the same thing. This machine needs to be operational as quickly | | as possible and I don't have 4-5 weeks to wait for delivery. | | Motors are usually quoted as being for voltages like 115, 230, 460, and 575. | But the nominal voltages are 120, 240, 480, and 600. Had you gotten the | correct voltage, it would have been labeled as for 460 and you would run it | on 480. If you were in Canada, you get the 575 version and run it on 600 | which is commonly available in Canada. | | So ultimately what you need is 600 volts. | | Does the machine require WYE (needs the neutral) or will it work on DELTA? | | There are several options. | | 1. | | A 480 -> 240x120 single phase transformer probably could be wired up as | a boost transformer. The secondary would be wired for 120 by paralleling | the two secondary windings. Then that winding would be put in series | with the primary. | | Draw an equilateral triangle on a piece of paper. Now draw extensions | on each of the 3 lines in the clockwise direction with a length of 25% | more. The ends of those extensions will be the boosted delta.
Oops. That's an extended delta and I forgot to calculate both extension legs. It would give you 668 volts (with an 8.9 degree phase shift), not 600. Boosting a closed delta is quite tricky; it gives some strange voltages and phase shifts. If there was a way to get a 60 volt boost instead of 120 volt, that would give you 572 volts (and 5.2 degree phase shift) and that might be close enough.
This is back to finding three unusual transformers already sitting around waiting for you.
Option 3 still seems viable, though expensive.
| I don't know the ratings you'd need. I've never done the capacity | calculations for buck-boost transformers. | | 2. | | If your power is coming in the form of 480Y/277, you could also boost | the 277 to 346 to get 600Y/346. Transformers are not made for these | voltage combinations, but you could use the 480 -> 120 for this in a | derated form to make 277 -> 69, and turn that into a 277 -> 346 boost. | This would simply extend the WYE hot legs. | | 3. | | You could build a delta-delta isolation transformer bank using *SIX* | single phase 600 -> 240x120 transformers running backwards. Wire | the transformers for 600 -> 240 (secondary in series). Now I will | refer to it as a 240 -> 600 volt transformer. Take TWO of them and | wire the 240 volt primaries in series and the 600 volt secondaries | in parallel. Now two of them make a 480 -> 600 volt transformer set. | Three such sets lets you make a closed delta. I'm guessing this can | be done with 50 kVA transformers (about $3300 at full list price, | which should be half that if you shop around, and maybe even less if | you find someone who likes the idea of selling six of them at once). | | Since you need them fast, call Canadian suppliers as these would generally | only be a stock item in 600 volt land (600 volts is rare in US). | | Are you going to get the vender of the machine that flubbed the order to | spring for the cost of these transformers? | | Be sure a competent electrician wires these, and properly tests the voltages | before closing the delta. |
--
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| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
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wrote:

three
were
rather
solution
recommend
like I

arrangement
quickly
575.
it
600
DELTA?
paralleling
generally
voltages
Thanx for the feedback. I was considering something along the lines of option 3 if all else failed. I got lucky though, thanks to the power of google I found a transformer on the shelf in Milwaukee. It's a custom job that the original buyer no longer needed. At 500KVA it's a bit bigger than I needed, but I'm not complaining as I can have it here early next week.
Thanks again for the feedback.
uray
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