3-phase Transformer, Y input, delta out: Hook up neutral on the input?

maxh · Apr 3, 2013

3-phase Transformer, Y in, delta out: Put neutral on the input? (running it backwards

Basically the title says it all. I have a 3 phase transformer (Square D 30T3H) in which the input windings are hooked up in a Y configuration and the output a delta. On the input, do I hook up the neutral?

Edit: I edited the title to reflect that I'll be running this transformer "backwards" (not that transformers care.) See my post 2 down for pics of the transformer and name plate.

mike_kilroy · Apr 3, 2013

quick ans: no

tell more?

maxh · Apr 3, 2013

mike_kilroy said:
quick ans: no

tell more?

Thanks!

This is for taking our 120/208Y 3-phase and getting 460 for a LeBlond Regal 15x30. I could re-wire the spindle motor for 230, but the rest of the stuff (shifter motor, worklight, coolant pump) would still be too low if I fed it off of our 208V. So I got this transformer from a friend. Large enough to run an entire small sized shop! (pics attached of transformer w/ cover removed and of name plate.) In the transformer pic, center bottom, you can see where the 3 input windings tie together and there is a hole there, making it possible to attach a wire, so I wondered if I should run the neutral there.

S_W_Bausch · Apr 3, 2013

mike_kilroy said:
quick ans: no

tell more?

I think I know what you will say, but I really shouldn't play EE, even on the internet

Please tell.

J.R. Williams · Apr 3, 2013

MAXH
Look at the transformer chart. The input, high voltage, is connected Delta and output is Y.

maxh · Apr 3, 2013

J.R. Williams said:
MAXH
Look at the transformer chart. The input, high voltage, is connected Delta and output is Y.

I don't see how it could possibly care which direction I run it. Especially since the lathe's only 7.5 HP.

Edit: I think I may have calculated HP rating wrong, but it's still a lot more than the lathe will require.
Edit 2: Doh! Thanks, J.R. That explains why the X0 is there; for 120V single phase when the Y is used as output, as it was designed. Of course I'm still going to use it backwards...

jmead · Apr 3, 2013

I'm interested in this too, I bought a load of similar transformers at a marina auction, 55 kva but similar taps and detla/wye 480-208/y120. All the ones I have in use are step down and wired as shown, but it's conceiveable I might want to hook one up backwards some day. In the back of my mind is a warning about grounding problems doing this but I don't remember the specifics.

adh2000 · Apr 3, 2013

maxh said:
I don't see how it could possibly care which direction I run it. Especially since the lathe's only 7.5 HP and this thing's rated for 40-ish HP.

The electrons don't care which way they are going. If you had 480 coming in you could get 208 three phase plus a neutral (center tap) that would get you 120V. But since you are going the other way you can just connect the three 208V lines and get 480V on the other windings. You do not need to connect the neutral. I do it all the time. Right now I have 3 transformers connected that way.

Froneck · Apr 4, 2013

First, a transformer works best in the direction it was designed to operate. Second you might want to think of how the transformer is connected. If it's connected 24/7 then that larger than necessary transformer is using power when the lathe is not running. That being said a transformer will work "backwards". I have a few connected "backwards in my shop simply because of cost. Why buy a new transformer and spend big bucks when a good used one will work almost as good "backwards". You want to connect Neutral? What neutral? there is no neutral in your transformer 480 Delta side. That hole you mention is the Neutral of the 208VAC Y connection X0 it has nothing to do with the Delta side. Ground and Neutral are not the same, A Neutral can be grounded! If your talking about ground then you might want to consider "Corner Grounding" or grounding one of the 3 outputs.

Frank

maxh · Apr 4, 2013

Froneck said:
First, a transformer works best in the direction it was designed to operate. Second you might want to think of how the transformer is connected. If it's connected 24/7 then that larger than necessary transformer is using power when the lathe is not running. That being said a transformer will work "backwards". I have a few connected "backwards in my shop simply because of cost. Why buy a new transformer and spend big bucks when a good used one will work almost as good "backwards". You want to connect Neutral? What neutral? there is no neutral in your transformer 480 Delta side. That hole you mention is the Neutral of the 208VAC Y connection X0 it has nothing to do with the Delta side. Ground and Neutral are not the same, A Neutral can be grounded! If your talking about ground then you might want to consider "Corner Grounding" or grounding one of the 3 outputs.

Frank

Thanks, Frank. It'll be disconnected in front of the transformer when not in use. But out of curiosity, how much power do you think this size transformer would waste, idling?

When I first looked at the transformer and posted the thread, I was under the impression this transformer was actually meant for the 208Y to be the input with the 480 delta being the output, not really thinking it through, or reading closely enough. Since there is a lug where the 3 legs of the 208Y tie together, clearly looking used, I wondered why the neutral would be there (remember, thinking it was on the input), and if there, does that mean I should use it. Of course, now that I know that the 208Y is designed to be the output, rather than the input, there's no question as to its purpose (giving 120V single phase capability.)

Froneck · Apr 5, 2013

Simple way to determine the waste of an un-used transformer is to measure the input amps when the load is not connected. Depending on the efficiency of the transformer the waste will increase as the load increases but it will be the price you pay to convert one voltage to another. Transformers are quite efficient, somewhat less when used "backwards". Though your not connecting a Neutral to "X0" DO connect a ground to the ground connection on the frame.
Frank

mike_kilroy · Apr 6, 2013

Froneck said:
Simple way to determine the waste of an un-used transformer is to measure the input amps when the load is not connected. Depending on the efficiency of the transformer the waste will increase as the load increases but it will be the price you pay to convert one voltage to another. Transformers are quite efficient, somewhat less when used "backwards".

Measuring no load loss indeed will tell the 'wasted power.'

A belief that run backwards, a transformer is less efficient, is a wives tale, and not true.

Froneck · Apr 7, 2013

A bit ago I needed to step-up Voltage at a company I worked for. Not wanting to use "wives tales" or simple "Bubba" connections I contacted a leading Transformer manufacture and discussed "Backward" connection. Dry type core transformers such as type type the OP posted are concentrically wound. Primary coils on the inner and outer winding with the secondary winding in the center. Done so to get the best magnetic coupling. To be Honest we talked about the Step-Down transformer I had therefore I do not know if Step-Up type has the coil configuration reversed. Reversing the connection increases the magnetic leakage slightly, or so I was told. Except for the small transformers 5KVA and smaller Transformers can be reversed without problems or KVA de-rating. However I was told that transformers are designed to work best as the name plate indicates at the highest efficiency. Reversing the direction will tend to lower the efficiency though not much. I assume this was fact because why would they make transformers with a Primary and Secondary? With this knowledge I connected the transformer backwards since the cost of a new transformer was far more than a saving in a few percent of efficiency. Keep in mind that I summarized the conversation as it was an hour long factual computation of transformer design most of which I have forgotten. What I did get was the answer I needed to shut-up someone that usually comes around to say I couldn't do what I did!

Heavey Metal · Apr 7, 2013

If you will look in your lathe control box there will be a control transformer with diferent taps and a diagram how to rewire the motor.

9100 · Apr 7, 2013

Froneck said:
Simple way to determine the waste of an un-used transformer is to measure the input amps when the load is not connected. Depending on the efficiency of the transformer the waste will increase as the load increases but it will be the price you pay to convert one voltage to another. Transformers are quite efficient, somewhat less when used "backwards". Though your not connecting a Neutral to "X0" DO connect a ground to the ground connection on the frame.
Frank

Much of the current in an unloaded transformer is VARs and a watt hour meter normally doesn't charge you for them. That is the old common ones. I don't know about some of the modern all electronic ones. To evaluate a transformer, you need a wattmeter, not just an ammeter. There is some loss, core losses and resistive losses in the primary winding. After all, they do get warm even when unloaded. There is a difference in efficiency when they are reversed, but you are not likely to notice it. Not just a wives tale, but not a big deal, either.

Bill

mike_kilroy · Apr 7, 2013

Froneck said:
.....Reversing the direction will tend to lower the efficiency though not much. I assume this was fact because why would they make transformers with a Primary and Secondary?

We use the term "primary" & "secondary" for customer ease of mine.... H1,H2,H3 for primary & X0,X1,X2,X3 - customers understand those terms.

When we make autotransformers, we continue this for customer ease of mind: but there is NO reason to do so - other than to keep folks comforable. Auto autxfmrs can have its pri or sec called the other with no difference.

That said, yes, some little nuances are SOMEtIMEs designed one way or another for inrush limiting and such on iso xfmrs, but once you get past the turn on, it is simple physics still.

maxh · Apr 7, 2013

I did a wonderful job of wiring up the transformer with conduit and everything, then looked harder at the wiring in the lathe's electrical panel and noticed that it looked like the internal transformer was wired for 230V instead of 460V. So I checked the spindle motor and it was also wired for the lower voltage. So despite the seller saying it was 460V, the government made info plate stuck to the front saying 460V, and the LeBlond sales rep telling me that serial number left the factory at 460V, it appears someone decided to change it to 230V.

They didn't do a very good job, though, because the shift motor was still wired for 460V. So I finished the job and the lathe's now running happily without an external transformer. Looks like trying to take the "easy" route led to more work in the end. (Big surprise...) Luckily I had been planning on eventually converting it to 230V anyways, so had already bought and run wire plenty suitable for the higher current draw.

Heavey Metal said:
If you will look in your lathe control box there will be a control transformer with diferent taps and a diagram how to rewire the motor.

The label on the internal transformer is pretty worn and I couldn't really read the diagram the first time I examined the wiring in the panel. It took some close looking and thinking (for me) to realize there were 2 input coils with the capability of being wired in series or parallel, and that they were currently in parallel, which means set for the lower voltage.

maxh · Apr 8, 2013

thermite said:
Not that I was actually hanging by my fingernails, not even being my shop or anything else, but still - perhaps the best news so far today.

Now - peddle that 30 KVA deep-meat-fryer and gain back some shop space ... before it tempts you to do something even more dangerous.

Bill

But I was going to use it at my desk to power a heated lumbar support and a homemade coffee mug warmer...

quasi · Apr 21, 2013

if you are using a transformer connected y to delta, the load on the delta, you need to install ground fault lights on the delta connection of the transformer. Check your N.E.C. (national electrical code)

2rods · Apr 21, 2013

Would you be able to use this transformer on single phase and how would you hook it up?

3-phase Transformer, Y input, delta out: Hook up neutral on the input?

Hot Rolled

Stainless

Hot Rolled

Attachments

Diamond

Hot Rolled

Hot Rolled

Hot Rolled

Titanium

Titanium

Hot Rolled

Titanium

Stainless

Titanium

Banned

Diamond

Stainless

Hot Rolled

Hot Rolled

Stainless

Aluminum

Similar threads