3 phase question Delta or Y ?

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  #1  
Old 04-13-11, 08:13 PM
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3 phase question Delta or Y ?

What is the difference? I am looking for a transformer (208 to 440 3 phase) to power a Hardinge lathe. I have 208 volt 3 phase available at my shop but would like to run a 440 volt 3 phase motor. So I've been watching Ebay to see what is up for sale. I noticed that some of the transformers list 3 phase Delta and others mention Y What is the difference and how do I know what the motor requires? Would it be stamped on it? Here is a link to the my thread where I was requesting info about transformer vs swapping the motor on this lathe

http://www.doityourself.com/forum/el...ml#post1842897

TIA TimH
 
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Old 04-13-11, 09:27 PM
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If you have 208v phase to phase, then you have Y service. Basically it has to do with the way the power transformers are configured.

However, if your motor is old enough to be rated for '440', then it most likely predates Y service and it won't be very happy with your 208Y. Even if the motor can be rewired for 240 (220 as it would be), it most likely would not tolerate 208Y. Aside from the voltage though, there is no difference between ∆ and Y as far as the motor is concerned. You will just need a 208-480v transformer for Y. Just remember though it's important to hook up the phases in the correct order, otherwise the windings in the motor will be fighting each other, or it will run in reverse.
 
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Old 04-14-11, 03:42 AM
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Thanks JersyMatt. I'm not sure how old the machine is. I'm guessing early 60s Its in nice shape but trying to figure out this whole transformer thing is driving me nuts. I think in the end once I find a transformer I will call an electrician to do the hook up.
 
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Old 04-14-11, 04:27 AM
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Basically new motors are designed for a wide range of voltages to accommodate any situation. A newer 3 phase motor would be configurable for either 208-240, or 480. In the olden days they basically only had "220" or "440", which were actually closer to 240 and 480, and that's what the motors were designed to work on. If you underfeed a motor like this (a 240v motor on 208v), it will pull more amps and generate more heat, which will break it down faster. But as I said, the type of 3 phase system doesn't matter to the motor. It's just that the type of system you have dictates your phase to phase and phase to neutral voltage.

The most common are 120Y208, 120∆240, and 277Y480. You have 120Y208, and as such you will need a 208-480 (1:2.31) Y transformer to run that motor. A transformer used for delta would be 240-480v (1:2). If you were to use the wrong one, you would end up with a voltage that is too high or too low (a ∆ transformer on 208v would only give you 416v, while a Y transformer on 240v would give you 554v).
 
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Old 04-14-11, 04:57 AM
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Thanks again. I'm starting to understand. I found this at a salvage/surplus place

15 KVA 3Ph 60 Hz High Volt: 480 Low Volt: 208Y/120 7 TAPS

Looks to be the right animal. Can you tell me what "taps" are?
 
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Old 04-14-11, 05:18 AM
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Taps are basically for 'fine tuning' the primary (input) voltage so that you get the desired secondary (output) voltage. So if your utility voltage is a little high or low, you can still produce your target output voltage.

Before you commit, check with the seller to make sure there is a proper wiring guide that is readable on the unit. Not much good to you if you don't know what the tap combinations are.
 
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Old 04-14-11, 10:22 AM
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A transformer with taps is actually ideal for your situation so you can bring the voltage down a little bit to accommodate the motor from the 440V olden days.
 
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