Step down transformer for Asia 2

[dtlxii]

I need a transformer for a machine being sent to Singapore. The machine uses 3-phase, 208 VAC, 30 Amps, 60 Hz. The plant supplies 3-phase, 415 VAC, 50 Hz. I know it should be around 15KVA rating but I'm not sure what transformer to get. Any help/suggestion is greatly appreciated.

 

[davidbeach]

No transformer is going to convert 50Hz to 60Hz. May or may not be a problem, but needs to be evaluated first.

 

[dtlxii]

Thank you. I know. Our machine can handle the 50 Hz. But I can't find anything for 415 VAC input. We need 208, Y-connection. I don't know if the customer has Delta o Y.

 

[waross]

For the use of a 60 Hz transformer on 50 Hz the following parameters must be down-rated in the ratio of 50Hz/60Hz.
Maximum voltage.
KVA
A suggestion;
A 480V:480V transformer configured as a 960V:480V auto-transformer will be suitable. Apply 416V to the 960V connection and take 208V from the 480V taps.
The size in KVA will be almost double what you actually need.
It will probably be a lot cheaper to call Hammond or another maker for a 50Hz transformer.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dtlxii]

Ok. What about using a 480/240 transformer, 50 Hz.? Would a 415 VAC input produce a 208 VAC output with no problems? Thanks for your help.

 

[DTR2011]

I believe what Waross is getting at is the Volts per Hertz ratio that must be maintained, else you will drive the core into saturation, hence his recommended specs.

 

[slavag]

mmm, maybe better add some VFD

 

[dtlxii]

Waross is right, but I think if I buy a 3-phase, 480/240, 15 KVA, 50 Hz transformer, I can use it in Singapore to hookup 415 VAC and get around 208 VAC, 50 Hz. Is this correct?

My equipment (208 VAC, 30 A) has components rated at 50/60 Hz so frequency is no a problem, but I was a bit confused by the 415 VAC requirement sent by the customer. I thought 480 was the norm.

Thank you very much for your help.

 

[jraef]

480/240 = 2:1 ratio. So 415 input will give to a 207.5V output. Whether or not the input is Y or Delta is immaterial (but it will be Y by the way). But a standard 480-240V transformer is not going to be Y on the output, it will be Delta only and you need Y on the output, so that isn't going to work. That is likely why waross suggested the other version, it is a way to end up with a Y on the side you need it on. Or like he said, have a custom one made.

If you go custom, then you have another issue. If a transformer is designed for 60Hz, applying 50Hz to it will put it into a low flux situation and the output capacity may be reduced because the magnetizing current will increase. So for the same amount of load on the transformer, it will run hotter at 50Hz and therefore the output capacity at full load will be reduced. So when you have a custom transformer made, make sure they know you are going to be using 50Hz up front, you can get into trouble if they build it for 60Hz.



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[waross]

Example;
A 60Hz transformer at 480 Volts has a V/Hz ratio of 8 Volts per Hertz.
At 50 Hz times 8 V/Hz the transformer will be rated at 400 Volts. (8 x 50) Saturation is a possible issue with a voltage above 400 Volts.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[busbar]

You might consider something like a “Group-U” [440Δ - 220Y/127V 3ø, 50Hz] transformer listed at

http://www.acmepowerdist.com/energy-efficient-transformers-three-phase.htm

 

[waross]

Good call busbar. That should work. lps

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dtlxii]

Thank you. Yes, I think that would work too. Just one more question. This transformer has a Delta input and Y output. Does it matter if the customer has a Delta or Y? I would think that it doesn't matter as they would not connect the neutral to the transformer if it was a Y, but I'm not sure. Thank you all for your help. This is the first time I have to spec something for another country.

 

[davidbeach]

Supply wye or delta makes no difference.

 

[waross]

You want to avoid a wye:delta arrangement.

Bill
--------------------
"Why not the best?"
Jimmy Carter