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08-26-2011, 11:27 PM #1
Wiring a 45KVA step-down transformer
Does anyone have a diagram on wiring a 45KVA isolation transformer from a cut-off panel to a machine?
- HV: 600v
- LV: 480
- 3 Phase
- 60amp from Cut-off panel (fused)
- 40amp 480v 3 phase to cnc mill
Any diagrams, feedback will help :-)
08-27-2011, 12:25 AM #2
look for it
Transformers usually have the wiring diagram somewhere on them. If not, an electrician can figure it out by looking at the windings. The windings with more turns will be the higher voltage ones, but transformers often have multiple taps at different voltages. Be careful!!
Btw, the current at the lower voltage will be HIGHER. If you fuse the 600V at 60A it will give you more current at 480.
08-27-2011, 12:58 AM #3
If you are not comfortable in your knowledge of doing this, please leave it to an electrician. This isn't 110 where a little bite is just annoying, something goes wrong here and it's a very large bang, usually with shrapnel, and intense temperatures. Arc flash burns can easily be life threatening and leave you disfigured for life........IF you survive......
08-27-2011, 02:45 AM #4
I agree wholeheartedly with Rainmaker and Tonytn36. If this isn't done correctly, there a possibility of blowing something up (yourself), starting a fire down the road, or damaging the machine you're connecting to the transformer.
I'll assume that this is a dry-type transformer. When you open it up, you'll see an iron core with three sets of windings - three single phase transformers. There are different ways to wire up the primary windings and secondary windings depending on the application.... Wye/Wye, Wye/Delta, Delta/Delta, Delta/Wye......
It's important that the proper winding configuration is used. For example, an ungrounded delta secondary might work for a while, but could lead to major problems down the road.
It's also critically important to protect the primary and secondary windings with the proper fuses or circuit breakers. Keep in mind that not all 60A fuses are alike.
Grounding is another important issue not to be overlooked.
A TTR (transformer turns ratiometer) is helpful in situations like this.
My advice: Hire a qualified industrial (not residential) electrician familiar with local codes.
One last pearl of wisdom passed down to me by a wise electrical engineer:
Q> Why do transformers hum?
A> Because they don't know the words.
08-27-2011, 03:07 AM #5
Wiring diagram - thoughts?
Thank you all for your feedback. Here are my thoughts. An electrician quoted me over $1,000 to get this wired up so what I was thinking is to to get all the components hooked up except for connecting the wire so the electrician only comes in to connect the wires up to make my ordeal cheaper.
Here is a quick wiring diagram that put together to garner some thoughts. I am also attaching larger pictures of each component involved in-case the connectors are not visible enough on the wiring diagram - any thoughts?
08-27-2011, 03:08 AM #6
Also attached are the panel decals from the transformer and bridgeport.
08-27-2011, 05:44 AM #7
It looks to me like you have it layed-out correctly. Your drawing showing the hook-ups is a little small and I little hard to read, but looks correct.
What you have here is a Delta to Wye connected transformer. The primary side is connected in a delta configuration. The secondary is connected in a Wye configuration. The point where all the wye legs come together is the X0 point on the transformer diagram.
The only item that I am not certain of is the grounding of the X0 point on the secondary of the transformer.
The way that you can get 277V power out of the secondary (as it is noted on the transformer data plate) is to use that X0 point. If the primary is hooked up to 600V power, you would see 277V from that X0 point to any of the X1, X2, or X3 points. You would also see 480V power between any of: X1 to X2, or X2 to X3, or X3 to X1. These are the points that you want to hook up to the machine - as you have drawn.
There are applications where you want that X0 point to "float" and not be grounded. There are applications where you don't want that point to float and you want it grounded. I believe that you can leave it gounded as it currently is, but I need to research that a little more. Maybe some else on the forum can comment on this.
I would hook it up as you have shown all the way up to the output of the transformer and then try it. I would measure the individual voltages between X1-X2, X2-X3, and X3-X1 by having the power disconnected and hooking up a volt meter - THEN hooking up the power and trying it. Repeat for each leg. DO NOT TRY TO MEASURE THE VOLTAGES WHILE HOLDING THE TEST LEADS AND MOVING THEM AROUND!. (see next paragraph) If you are getting 480V as mentioned, then hook up the transformer to the machine switch and try it. Use appropriately sized wire. Calcualte the amps and pick the correct wire size from a wire size chart.
As a previous poster has mentioned - a "zap" from 110V is annoying. A "dry" zap from 220V will hurt (stupidly, I speak from experience here). A "wet" zap from even 220V can be fatal (thankfully I haven't experienced this yet). Almost any zap from 440V and higher can kill you (lots of stories). It only takes 1.0mA of current through the heart to kill you. That is 1/1000 of ONE amp. It's not a lot of current. Assuming the average body resistance is somewhat constant, any increase in voltage makes the chance much greater that a lethal dose of current will pass through the heart. So, disconnect the power ANYTIME you are playing with wires in high voltage systems (OK - ANY system). Or, have the electrician do the "dirty work."
Let us know when you get it set up and your machine is running.
08-28-2011, 12:48 AM #8
In this situation, don't float the neutral (X0). You'll want to ground X0 for safety and machine longevity reasons.
The little green wire from X0 to ground probably isn't adequate.
If I were doing this, I'd run a ground wire from the primary disconnect, to the transformer and frame, and also to the machine ground. Ultimately, it'll need to be tied into the building steel and/or ground rod.
After looking at your diagram again, it looks like you're on the right track.