running 480v machine on 380v

winnie said:
480V is a common generator voltage. If the generator is designed for 480V then there are no issues with this approach.

Does the generator have a 12 lead alternator? Different voltages are usually a combination of excitation change and alternator connection. In the systems I've worked with, excitation could adjust the coil voltage from 120V to 140V, then the coils would be connected differently to get 208V, 240V, 416V or 480V.

I would be concerned about the components outside of the alternator if they are not specifically designed for the higher voltage.

D
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Yes I think I will be able to find 12 leads alaterantor. That’s true .I have to concern about generator controller ,relays and contractor.


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Emad said:
Yes@tortuga
We are now using type L outlets and power system is 380/220v 50hz.
However,there are a little number of old Oil fields that they still use 220y110 ,whose I believe established by Amharic companies in early 1960s


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Yes, that was my experience. I also used 11kV for some projects. Might have been specials,
 
Emad said:
Yes I think I will be able to find 12 leads alaterantor. That’s true .I have to concern about generator controller ,relays and contractor.


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I suspect that a standard generator with a 12 lead alternator will be rated for use up to 480V. But I agree, the issue is confirming you get a generator rated for the voltage.

Back in your original post, you said that the proper transformer was not available. I was wondering if you'd given any thought to my suggestion of using 2 or 3 standard single phase transformers to get your desired transformation ratio. What sort of single phase transformers can you easily get?

-Jonathan
 
winnie said:
I suspect that a standard generator with a 12 lead alternator will be rated for use up to 480V. But I agree, the issue is confirming you get a generator rated for the voltage.

Back in your original post, you said that the proper transformer was not available. I was wondering if you'd given any thought to my suggestion of using 2 or 3 standard single phase transformers to get your desired transformation ratio. What sort of single phase transformers can you easily get?

-Jonathan
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Single phase transformers with capacity larger than 5kva are not common here
All Workshops I reached here can do the rewinding only .
I found 3ph transformer 380/110c but with 30kva
Some body suggested to use it as open delta auto transformer ,but 30kva capacity is not sufficient


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Emad said:
Single phase transformers with capacity larger than 5kva are not common here
All Workshops I reached here can do the rewinding only .
I found 3ph transformer 380/110c but with 30kva
Some body suggested to use it as open delta auto transformer ,but 30kva capacity is not sufficient


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1) Can you get 5 kVA 240:120V single phase transformers? Three such transformers in a wye boost configuration would give you about 41kVA of capacity at 570V.

2) Can you get 5 kVA 380:110V single phase transformers? Two such transformers in an open delta boost configuration would give you about 38.5 kVA of capacity at 490V. Three such transformers would in a sort of 'stretched delta' boost configuration would give you about 43.5 kVA of capacity at 553V

3) What is the full configuration of the 3 phase transformer that you've found, primary voltage, secondary voltage, and winding configuration (wye, delta, etc.). Can the workshops do things like reconnect the transformer winding terminations if necessary?

-Jonathan
 
Emad said:
Single phase transformers with capacity larger than 5kva are not common here
All Workshops I reached here can do the rewinding only .
I found 3ph transformer 380/110c but with 30kva
Some body suggested to use it as open delta auto transformer ,but 30kva capacity is not sufficient


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Winnie covered it well. I was going to say that with autotransformers, you don't need to meet the full kVA of the equipment, on the rated amps times the difference in voltage.
 
winnie said:
1) Can you get 5 kVA 240:120V single phase transformers? Three such transformers in a wye boost configuration would give you about 41kVA of capacity at 570V.

2) Can you get 5 kVA 380:110V single phase transformers? Two such transformers in an open delta boost configuration would give you about 38.5 kVA of capacity at 490V. Three such transformers would in a sort of 'stretched delta' boost configuration would give you about 43.5 kVA of capacity at 553V

3) What is the full configuration of the 3 phase transformer that you've found, primary voltage, secondary voltage, and winding configuration (wye, delta, etc.). Can the workshops do things like reconnect the transformer winding terminations if necessary?

-Jonathan
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Thank you Jonathan
This can probably solve the problem .I can find all of these ranges
I hope if you can be more generous with me and teach me how you did the maths for the three cases
Also:
Do you mean by open delta to connect the primary of two phase in series with their secondaries and get the output across the two windings?
What about stretched delta ?
I should be very appreciative if I get any sketches


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You are going to be the engineer of record, so you will need to go and read a document about how autotransformers work; I will give you a summary concept of things.

1) A 'buck/boost' transformer or 'autotransformer' is a configuration where your secondary coils are connected to your primary circuit. The secondary voltage adds (or subtracts) from the primary voltage, rather than being 'separately derived'. The key for sizing an autotransformer is that only a portion of the power delivered to the load actually goes through the transformer. Most of the power is actually delivered directly from the primary circuit.

Here is a single phase example: you have a 208V supply but need to support a 230V load. To supply this load you select a 1 kVA 240:32V transformer. You connect the 208V supply to the 240V primary (remember you can use a transformer at less than its rated voltage). The secondary voltage is 27.7V. You connect the secondary in series with the primary, so that the total voltage you get is 235.7V, hopefully close enough to the required voltage.

Now to determine the capacity of this arrangement. Remember that we started with a 1 kVA transformer. You calculate the _rated_ secondary current; this is just 1000/32=31.25A. (Not 1000/27.7, to figure the rated current you use the rated voltage). The total output voltage of the arrangement is 235.7V so the rating of the complete arrangement is 235.7V * 31.25A = 7.4 kVA. Important: only 1 kVA is being 'processed' by the transformer; the other 6.4 kVA is being supplied directly from the primary. If you map out the current flow, your supply is sending 35.42A @ 208V to the transformer. 31.25A goes through the secondary, 4.17A goes through the primary.

1745972684651.png

2) I won't do the calculations but will show the 3 plausible configurations:
open delta:
1745972930036.png
wye:

1745973093307.png
skew/stretched delta:
1745973271110.png

I doubt you will find the last one in a text book, and there is probably a good reason. I like it because it is symmetrical but doesn't have a neutral that you can't really use.

Hope this helps
Jonathan
 
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