Step Up Transformer 3p 208 to 480 20kva

Hey guys,

I recently bought a machine. It's an oil purifier made by Pall, model HVP-902. This machine was originally designed to operate on 220 3 phase. Sometime in it's life the operating voltage was changed to 480 3p. It's no big deal to switch voltage on the motor and reconfigure the step down transformer for the electronics that run on 110. I determined I need to replace the main breaker which is 50 amps at 480v. There are also some contactors that may have been changed. As I was researching what I might need to get, I had called the company and spoke with guy that had originally built this particular unit. He had asked if the heating element had been changed. I said yeah, it is set up for 480. Well, the special heating element for 220v in this oil purifier is 10 times what I paid for the unit itself. So no, it seems the path of least resistance (or cheapness) is to change back the wiring I altered and use a transformer to step up from 208 3p to 480 3p somewhere in the 15 to 30kva range. The machine calls for 53 full load amps at 220 so 15kva is the smallest I can go with. I prefer to stay around 20KVA to get away with a 100 amp breaker.

The problem I am having is I can find a bunch of transformers that step down from 480 to 208. But, I can't seem to find one that steps up. Can one of those 480 down to 208 be reversed to act to step up voltage?


thanks in advance,
Mark

For the most part, a transformer is just a ratio changer. It doesn't really care which is line or load, it's just high side and low side. There are sometimes minor issues with the way the windings are configured that can cause some nuisance tripping of protective devices, but that's somewhat rare in my experience.

In the case of 208-480 Step-Up use, there are issues regarding the fact that the 208 side is almost invariably going to show on the nameplate as a "Wye" configuration where you would normally (ie in Step-Down) connect the X0 terminal to ground as a Neutral. For stepping up, you do not want to do that. But I think the Code may require that on the High sode if it is a 480/277V H side, even if you do not use the 277V to Neutral in the machine (which most likely you will not).

Thanks for the reply. I've found that 20kva is the minimum size I could go with. 20 doesn't seem to be a popular size though. The next one up for common size is 30kva.
I am not sure about the delta and wye configurations and how to apply them.

I did find a 30kva for 208 to 480.
30 KVA Vented Distribution Transformer 3PH 208 480 277V Jefferson 423 7191 000 | eBay
This seems like what I need. However, I'd love to find a used unit for cheaper. Any comments on this transformer?

Here is a 480 to 208 transformer, which is much cheaper and more common: Square D 30 KVA 480Y 277 3 Phase Transformer | eBay

So, can a unit like this Square D be run backwards? Having just enough knowledge to not get electrocuted, yet not nearly enough to be creative, I kinda need a "put this wire here" diagram.

This machine is going to be located on the other side of the shop from the breaker panel. So, I have the cost of running conduit, pulling wires, mounting an outlet and adding a 3p breaker. These costs will be there regardless of voltage choice. There are a few senarios on how to get this oil purifier wired in.

1. Leave the 480 set-up in the machine and simply add a step-up transformer. This adds about $1500 to the new circuit.

2. Change the breaker, contactors, heating element and anything unforseen that might be needed for the swap to 220. $3000, maybe more.

3. Change the breaker, contactors, and other unforseen. Yet, leave the 480 heating element. Put a 15kva step-up between the control panel and heating element. $2000, maybe more.

Money doesn't come for free. But, doing something the best way is more important. Other than cost, does one of these senarios prove to be superior? Or, is there a better way?

thanks,
Mark

Man we have 4, 480 to 208 backwards feed transformers in our shop. So, 208 wye in, and 480 delta out. Don't connect the Ntrl, and remove the Ntrl to frame tie strap. But do ground the box. There may be others, so do some research for your application.

I didn't pay more than 200 bucks for any of them, call around to industrial salvage places, irrigation, machine rebuilders, scrappers, run ad in cheap local rags "wanted" xxxx.

I take that back, one of the damn near new 30KVA we paid 250 for....

Wow, awesome. I was hoping the hear that. I have been reading about Delta and Wye, until my head was spinning. Not, 100% sure, but I believe my shop is supplied 208 3p in wye. The Jefferson 30kva step up transformer lists it requires 208 delta and makes 480 wye. So, this doesn't sound like what I need. I believe I need the opposite, 208 wye to 480 delta. Seems like the hurdle isn't going to be as tall as I thought to get this machine hooked up.

thanks for the info,
Mark

FirstEliminator said:

Wow, awesome. I was hoping the hear that. I have been reading about Delta and Wye, until my head was spinning. Not, 100% sure, but I believe my shop is supplied 208 3p in wye. The Jefferson 30kva step up transformer lists it requires 208 delta and makes 480 wye. So, this doesn't sound like what I need. I believe I need the opposite, 208 wye to 480 delta. Seems like the hurdle isn't going to be as tall as I thought to get this machine hooked up.

thanks for the info,
Mark

Click to expand...

The Delta and Wye is in how it is connected and used. You will have 208V Wye as a service, every 208V service I have ever seen is like that, because in addition to it providing 208V line-to-line, it is inherently 120V line-to-neutral, so it supplies your outlets and lighting without the need for anything else. In that Wye service, the neutral is created by grounding the Wye point, or the "X0" terminal.

But when you are going to use a standard transformer to step-UP, you do NOT want to connect the neutral or ground that you already have to the Wye point of the 208V side, it can cause high current to flow in the Neutral if there is even the slightest imbalance, and there always is. No need to learn Electrical Engineering to fully grasp it all, just trust us.

So what I meant earlier is that when you look at the diagram for the 208V side of a standard step-down transformer that is used to get a 208Y120V output, it will show 3 line connections to X1, X2 and X3, then a 4th to X0, which is the "Wye" point, and it will show that is to be connected to ground to form a Neutral. But that is NOT what you want to do here, so just DO NOT connect anything to that X0 terminal at all, and if there is now anything connected, i.e. the "Ntrl to frame tie strap", then REMOVE IT.

However...
In the two links you posted, BOTH of them are ironically NOT standard step-down transformers, they actually appear to be SPECIFICALLY for stepping UP to a 480Y277V output. In my opinion, you should get one of those. That's because on the 480V side, you WANT a 480V Wye, not 480V Delta, even though you are not really going to be using the Wye functionality (277V single phase). The Code requires that the 480V side be referenced to ground, OR you have to provide some rather expensive ground fault equipment. If you have a 480/277V transformer, you can ground the H0 terminal of the Wye and satisfy that requirement. Otherwise it's either the GF protection, or you have to use what's called a "corner grounded delta" configuration and for a novice, I don't recommend it.

Confused yet? I know it's easy to get lost in all the jargon, but here's the bottom line:

Step one: Buy one of the ones that is 208 Delta to 480/277 Wye, that is going to be the easiest for you to handle. Both of those are essentially identical in all ways, I would buy the Sq. D one.
Step two: Connect your 208V to X1, X2 and X3, connect your 480V side to H1, H2 and H3, then connect H0 to ground. Done.
Step two-and-a-half: You will not be connecting anything in your machine to the new "Neutral" of this transformer, but that doesn't matter. You are connecting it to ground just to satisfy the code requirement, which is actually about some long boring safety issues that you don't really need to know here.

Thank you very much for the info. I did purchase a Westinghouse 30kva transformer today.

http://www.ebay.com/itm/261098582712?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

It will probably arrive early next week. Once I figure out where to mount the transformer, the next step is the run conduit and wiring. Also, add a circuit to the panel. I believe a 100 amp breaker is what I need as a 30kva transformer will pull up to 83 amps on the primary side with 208. I am anxious to try out this oil purifying machine. Hopefully it works as good as they claim.

thanks,
Mark

FirstEliminator said:

Thank you very much for the info. I did purchase a Westinghouse 30kva transformer today.

WH 30 KVA 480 x 120 208 Volt Encapsulated Transformer T719 | eBay

It will probably arrive early next week. Once I figure out where to mount the transformer, the next step is the run conduit and wiring. Also, add a circuit to the panel. I believe a 100 amp breaker is what I need as a 30kva transformer will pull up to 83 amps on the primary side with 208. I am anxious to try out this oil purifying machine. Hopefully it works as good as they claim.

thanks,
Mark

Click to expand...

Well, now you went and bought one that IS a step-down transformer, so you WILL have a Y on the 208V side and you must NOT connect the X0 terminal. Then on the 480V side, it is a Delta only. That then means that per the NEC 250.21 (B), you must either ground one corner of the transformer windings (which freaks some people out and has a list of rules to follow), or install a ground fault detection system. Don't say I didn't warn you...

Might be time to hire an electrician.