Anyone experienced with transformers? Adding a 440V machine to 220V 3 phase

[Phillip Mitchell]

I know this is somewhat basic, but I’m inexperienced with transformers and looking for some confirmation / advice. I have a few questions about adding in a 440V machine to my 240V system.

I have a 10 HP Kay Phasemaster RPC that’s fed 60 amps single phase at 240V and has a 30 amp 3 phase receptacle on output side. This runs my planer, one of my table saws, and a shaper (one at a time.) I have gathered all the parts and pieces for a 125 amp 3 phase MLO panel on the output side with a 20 amp circuit (shaper power feed, drill press) and a 30 amp circuit (planer, table saw, shaper) The wiring/installation for all this is about to begin.

I am soon adding a Solberga drill press with a 2 speed motor that is 440V only. The motor tag says 2.0 amps at 440V. It does not appear to be a dual voltage motor and I think this is fairly common with these presses to have it be only 440V.

I don’t plan to add anymore 440V machines, but...

What size transformer do I need to run the drill press? According to my napkin math, a 2.5kV transformer would do it, but I may be miscalculating.

Aside from eBay and Craigslist and asking my electrician neighbor, where are you guys finding surplus transformers. I’m hoping to find something for less than $250-300 semi locally.

Where do I add the transformer past the RPC? Obviously I still want 240V 3 phase for all the other machines. Maybe I should add a second 20 amp circuit / breaker in the MLO that is dedicated to 440v with a transformer downstream of that?

It seems that most transformers are meant to step down voltage instead of step up. Can they be wired “backwards” in this case without any practical issues?

I can afford to wait a little bit (month or so) for a good deal to surface on what I need, but much more than that and I’ll be getting antsy and needing to have the press running.

What else do I need to know that I am overlooking as far as transformers go?

Thanks so much for any input.

-Phillip

[Rod Sheridan]

Hi Phillip, a 2KVA transformer would be adequate.

You'll need an auto transformer, not an isolation transformer unless you can find a transformer with a WYE secondary at 480 volts. (doubtful).

I presume that this is for use in a commercial establishment?

Regards, Rod.

[Eric Arnsdorff]

The motor rating of 440 VAC / 2 amps 3 phase is slightly over 1.5 kVA load {P (apparent power) = sqrt(3) * V * I}. So yes, a 2.5 kVA transformer would handle that load.

Unfortunately, 3 phase transformers require 3 sets of windings which does increase the cost. You're looking for a delta to delta autotransformer.

Generally speaking you should be able to apply the voltage to either side of the transformer. The thing that can happen when doing this is inrush current may be more than expected if used in reverse. Most likely you will be fine though. They may be called Buck, Boost, General Purpose, etc. Basically, it's a box with 3 windings which each winding has various taps (literally a wire pulled out at a certain number of turns). The autotransformer uses a common winding while the more expensive and larger isolation transformers have 2 independent windings per phase. You can use an isolation transformer but it isn't needed for your application.

Make sure you provide the appropriate over temperature and over current protection for the transformer if it isn't part of the assembly you purchase.

I haven't shopped for used/surplus transformers so I can't help you with where to find those. There are a number of sources for new transformers and this ratio is readily available.
One other quick note is 440 VAC 3 phase is also referred to as 460 & 480 VAC. So if you find a 480 VAC rating it will also be fine for the 440 VAC. This is an insulation as well as creepage and clearance aspect of the design. Just make sure the ratio is correct. Also, at 480 the motor is expected to run a little less than the rated 440 VAC current indicated (although the particular motor design can affect this and does sometimes surprise me - it's about the V/f ratio which affects the magnetic flux and such - nothing of concern for your equipment as long as the motor frequency and voltage match what you give it).

[Bill Dufour]

Take the motor in to a good motor shop. It is likely they can get to the internal leads and switch it two 240 volts. Or another motor is probably cheaper then a transformer.
I believe you can use three single phase transformers in parallel?
Bill D

[Mike Henderson]

I agree with Bill. If at all possible, I'd change out the motor(s), and probably go single phase. As Eric pointed out, that motor is only 1.5kVA which is probably less than 2HP. You can easily run 2HP on 240 volts single phase.

If you try to use transformers with three phase, you have to have a transformer for each phase.

Mike

I don't know if they make VFDs that will step up the voltage from 240 volts to 440 volts but if they do, that's another way to run the motors (240 volts single phase in, 440 volts three phase out).

[Phillip Mitchell]

Changing out the motor is not a practical option. This is a geared head drill press and the motor is integrated into the head of the drill press and directly running the gears, not a belt drive.

It seems fairly straightforward to add a transformer and plenty of folks have done it - I’m just trying to wrap my head around the nitty gritty of it so I have a better idea of what to look for on the used market and exactly where to place it in the circuit.

Rod, This is not in an industrial setting, but in my shop which is on my property.

[Rod Sheridan]

Thanks Phillip, where I live there's a prohibition on voltage to ground in dwellings exceeding 150 volts, which is why I asked about your situation.

480 volts line to line is 277 volts to neutral (ground).

That's why you need a WYE secondary with the neutral grounded, or an auto-transformer which maintains the ground reference from the incoming system..........Regards, Rod.

[Mike Henderson]

Have the motor wired for 220 to 240 volts and use a VFD to drive it.

Mike

[Phillip Mitchell]

Have the motor wired for 220 to 240 volts and use a VFD to drive it.

Mike

Mike, the motor is integrated inside of a sealed and oiled case that houses the gears that operate the press. Not the same thing as pulling a belt off and unbolting 4 bolts and taking a motor to a motor shop to rewind.

The press looks like this. Also the motor tag states that it’s a 440V only motor, so it would mean a rewind to 220V, which is not the same as re-wiring a dual voltage motor, unless I am missing something.

This is also a 2 speed motor, so to use a VFD I would need to wire it to either the low speed or high speed and loose the 2 speed control, which I’m not convinced is the right decision on this particular machine.

It also has a power down feed control that I’m not sure if the VFD would need to bypass or not...basically not interested in a VFD for this particular machine for various reasons. I have a nice 5HP VFD on my Oliver jointer and it’s great as the machine came to me without switch controls and the VFD stops the cutterhead in about 7 seconds, so I know their value. Seems simpler to find the right transformer and not modify this particular machine.

[Phillip Mitchell]

Make sure you provide the appropriate over temperature and over current protection for the transformer if it isn't part of the assembly you purchase.



Eric,

Thank you for the detailed reply. How would I know looking at different available transformers if they have this protection integrated or not? If not, what do I need in place to protect the transformer?

[Mike Wilkins]

Get some advice from your local electrical motor shop. These folks can point you in the right direction.

[Phillip Mitchell]

I’ve called 2 local electric motor shops and they’ve both passed me off to the electrical supply houses, which don’t actually stock anything and would be ordering (new) transformers from another source and marking them up. Thanks for the reply, though.

Some searching has turned this up somewhat locally for $325 (photos attached.) According to my research, this transformer seems like it will work for what I need if I can wire it backwards, which I have read is fine.

Can anyone confirm this based on the info from the original post?

Just to be clear, I will be using a licensed electrician to help me install the transformer.

[Eric Arnsdorff]

Eric,

Thank you for the detailed reply. How would I know looking at different available transformers if they have this protection integrated or not? If not, what do I need in place to protect the transformer?

Phillip - If there is protection available it will likely be very obvious.

Most transformers of this don't have anything built in.

The 2 types of protection are an Overcurrent Protective Device (fuse or circuit breaker) and a thermal switch.
Sometimes fuse kits are available to mount directly on the transformer and this would be obvious if it were there. Similarly, a circuit breaker(s) would be visible and obvious.
A thermal switch will be embedded in the transformer with leads out out to a terminal block typically. If it has a thermal switch it will be shown on the connection diagram on the transformer. I utilize thermal switches in what I do but most standard transformers of this size won't have a thermal switch. It also must be connected to a means to open the circuit.

Basically, use of the thermal switch allows less requirements on the OCPD.

NEC has good design rules to follow and it gives several options. You can have a lower amperage primary OCPD and eliminate the secondary OCPD. A simple first pass is use a 125% rated OCPD on the primary and you will be safe. There are various options and such but if you have margin in the transformer then that would likely be all you need. You can find specs from the different manufacturers of either the transformer or OCPD devices. Littlefuse is one I've used for fusing and they have some guidelines you can look up. It's really fairly simple, just a lot of options.

[Eric Arnsdorff]

Phillip,
That transformer definitely would work. It appears to be a 4 kVA and well oversized for what you need but if the price is good for you then it looks like you're set.

[Bradley Gray]

Phillip, Check this out:

http://www.southlandelectrical.com/search.html?keywords=3p+transformer#2

Southland sells new and used elec components.

[Rod Sheridan]

Hi Phillip, that's an isolation transformer, not an auto-transformer.

You need a Wye secondary (480 volt) with the neutral grounded, or an auto-transformer which is smaller and less expensive......Rod.

[Bill Dufour]

A single voltage motor may very well have internal wiring for a lower voltage. It just means the maker did not bring those connections out to the junction box. They have to open it up and fish around looking for the splices and bring new leads out to the junction box. Of course they may be deeply buried and not possible to get too or they may not exist inside there at all.
Bill D

[Phillip Mitchell]

Well, just to update this thread a bit - after inquiring with several electric motor shops in the surrounding area, many of which said something to the effect of “uhh, no we don’t have anything like that...”, I was referred to an electrical supply house in Knoxville, TN that sells surplus and refurbished transformers.

The closest they had to my needs was a 7.5 kVa Acme 3 phase dry auto transformer that is 460v primary to 230v secondary for $100 + about the same amount in freight shipping. I’m of the understanding that I can backfeed it to go from 230v up to 460v.

The bummer of it is that earlier that day I was in Knoxville picking up the drill press in question and simply didn’t know about them at that point in the process and could have just gone by there and picked it up in person. ~ $200 for a tested 3 phase transformer is way cheaper than I’ve been able to find anything online in the last couple weeks and a lot of what I’ve seen is untested.

I will update the thread once I have the transformer and get it all wired up. Hopefully this will be what I need to run the drill press.

Here are a few photos of the drill in question - should be a sweet setup when it’s up and running. 8 Speeds from 100-2200 (tel:100-2200) RPM, 1.5 hp motor, MT3 spindle, Power down feed option with 4 different speeds, 360 degree production table that can adjust all the way down the column. The quill depth is about 5 1/4”. The head also has up and down travel of about 10-12”, overall weight is 220kg (485#) but is more compact than many much smaller capacity belt drive models.

[Scott T Smith]

Phillip, I have done what you're trying to do. I concur with the advice for the 7.5kva dry pack.

In my shop, I have a 400hp 480VAC generator that feeds an 800 amp 480 three phase panel board. This panel board also supplies a dry pack transformer that I use as a step down transformer to feed a 400A 240 three phase panel board via a transfer switch.

I also have a 30 hp rotary phase converter that feeds the same transfer switch as the dry pack. This setup allows me to feed the 240 three phase panel from either the RPC or the generator (via the step-down dry pack transformer). I am able to use the RPC for most of my 240 three phase loads, minimizing generator run time.

I have 15 hp 480V sawmill edger that I also run off of the RPC. There is a breaker in the 240V three phase panel that supplies a small 240 to 480 dry pack that is slaved to the edger.

So, the RPC powers a 240 3 phase panel board. The 240 panel board has a breaker that supplies a 240/480 3 phase dry pack transformer, which then feeds a 15hp 3 phase motor. The setup works fine.

[Eric Arnsdorff]

Well, just to update this thread a bit - after inquiring with several electric motor shops in the surrounding area, many of which said something to the effect of “uhh, no we don’t have anything like that...”, I was referred to an electrical supply house in Knoxville, TN that sells surplus and refurbished transformers.

The closest they had to my needs was a 7.5 kVa Acme 3 phase dry auto transformer that is 460v primary to 230v secondary for $100 + about the same amount in freight shipping. I’m of the understanding that I can backfeed it to go from 230v up to 460v.

The bummer of it is that earlier that day I was in Knoxville picking up the drill press in question and simply didn’t know about them at that point in the process and could have just gone by there and picked it up in person. ~ $200 for a tested 3 phase transformer is way cheaper than I’ve been able to find anything online in the last couple weeks and a lot of what I’ve seen is untested.

I will update the thread once I have the transformer and get it all wired up. Hopefully this will be what I need to run the drill press.

Here are a few photos of the drill in question - should be a sweet setup when it’s up and running. 8 Speeds from 100-2200 (tel:100-2200) RPM, 1.5 hp motor, MT3 spindle, Power down feed option with 4 different speeds, 360 degree production table that can adjust all the way down the column. The quill depth is about 5 1/4”. The head also has up and down travel of about 10-12”, overall weight is 220kg (485#) but is more compact than many much smaller capacity belt drive models.

That's a great price for a transformer that size! I'm glad you found what you needed!

I live in Knoxville, Tn and I'm curious what shop you found it at? Small world!

[Phillip Mitchell]

That's a great price for a transformer that size! I'm glad you found what you needed!

I live in Knoxville, Tn and I'm curious what shop you found it at? Small world!

Eric, the place is called Volunteer Equipment and Supply in Knoxville. It sounded like they have quite an inventory on surplus transformers of a wide range of sizes.

[Charles Lent]

Contact Acme Transformer in Lumberton, NC http://localautomation.com/profiles/acme-electric.html I was the US Factory Electrical Service Engineer for a Czech Republic company, installing and servicing large machinery for them in the US and Caribbean, and had to have some special 3 phase transformers built. These guys did it at a very reasonable price and what they sold was UL accepted. You will be dealing directly with the guys who make them. If they have a standard product that will fill your need, they won't push you into a special either. Their sales force is very good at helping you pick out what is needed.

Charley

[Bobby Robbinett]

Can you guys elaborate on using a transformer in reverse? I got a 240v 3ph primary & 480v 3ph secondary transformer with a machine that I purchased recently. I have 240v 3ph in my shop already (no phase converter, real 3ph) so I don’t need this transformer but I am looking at another machine that is 440v 3ph and I am wondering if I could use this same transformer in reverse as you guys described it?

[Rod Sheridan]

Hi Bobby, yes a transformer can be reverse fed, except where prohibited by code (for example if the manufacturer labels one end primary, then that has to remain the primary).

The issue with reverse feeding a standard Delta/Wye transformer is that now the Delta becomes the secondary, and you wind up with an ungrounded floating system, which can be very dangerous due to induced potential as well as the issue of detecting ground faults.

You really need an auto-transformer for your application, or an isolation transformer of the correct configuration.............regards, Rod.

[Mike Henderson]

The other approach is to get three single phase transformers of the correct voltage conversion and then you can hook they up any way you want. That is, you can hook them up delta or wye in the primary and wye in the secondary.

Mike

[Charles Lent]

Hi Bobby, yes a transformer can be reverse fed, except where prohibited by code (for example if the manufacturer labels one end primary, then that has to remain the primary).

The issue with reverse feeding a standard Delta/Wye transformer is that now the Delta becomes the secondary, and you wind up with an ungrounded floating system, which can be very dangerous due to induced potential as well as the issue of detecting ground faults.

You really need an auto-transformer for your application, or an isolation transformer of the correct configuration.............regards, Rod.

You can ground one leg of a delta transformer output and it will be safe. This is a common and required practice. You will still have the rated output between the three phases, but the grounded phase will, of course, read zero voltage between it and ground. The output windings of a transformer are isolated from the input, so you need to provide a way of grounding this output as it is a derived source that is otherwise ungrounded. If the secondary is left ungrounded, any leakage through the insulation between the primary and secondary windings of the transformer could result in very high voltages being present between the secondary and ground. It's not so bad if the primary voltage is low, but a transformer with a 12,000 volt primary and 240 volt secondary that has no ground on the secondary could possibly have as high as 12,240 volts to ground on it. This is why grounding of the secondary is a "must" in almost all cases.

With a Delta system, 3 single phase transformers can be used instead of a 3 phase transformer which is just 3 transformers packaged together. For grounding of the output, just ground one of the outputs as noted above. Do not do this if you go with an auto transformer system, since the output of an auto transformer is still grounded at the source. Only add the ground when an isolated secondary winding is in use. An auto transformer is a single winding with a tap at the desired output voltage, so the input is already grounded at it's source, and you are just using a higher voltage tap on this one winding for the output.

Charley

[Phillip Mitchell]

I appreciate the continued commentary on the subject, though I must say that most of it is going over my head, which is fine.

Let’s go back a few steps. I have found this tested and used 7.5 kVa dry auto transformer for a great price that has a listed primary of 460v and a listed output of 230V. I want to do the opposite and end up with 440/460v on the output side with 230V incoming. Can I (my electrician) safely backfeed this transformer and what do I need to know to do so safely?

[Rod Sheridan]

I appreciate the continued commentary on the subject, though I must say that most of it is going over my head, which is fine.

Let’s go back a few steps. I have found this tested and used 7.5 kVa dry auto transformer for a great price that has a listed primary of 460v and a listed output of 230V. I want to do the opposite and end up with 440/460v on the output side with 230V incoming. Can I (my electrician) safely backfeed this transformer and what do I need to know to do so safely?

Yes, IF the jurisdiction you reside in does not have a requirement that transformers with primary and secondary designations are correctly connected.

If the auto-transformer is simply marked H1,H2,H3/ X1, X2, X3 or something similar then yes.

If it clearly states primary and secondary you'll have to check with your electrician as to local rules.

I don't expect that you'll have a problem...........Regards, Rod.

[Joe Calhoon]

Philip,
I don’t think you will have any problems. I’ve had two 480 primary- 240 secondary working in my shop for years. Incoming is 240 3 phase making 480 going out. Never an issue with these.

[Phillip Mitchell]

Thank you Rod and Joe. I appreciate the replies...puts me at ease a bit. Hopefully I will receive the transformer tomorrow and begin the wiring soon.

[Tom Bender]

Have you had this conversation with your electrician?

As the saying goes, no battle plan survives contact with the enemy.

[Phillip Mitchell]

Have you had this conversation with your electrician?

As the saying goes, no battle plan survives contact with the enemy.

Hah. Yes, to a point. I asked him initially for recommendations on where to source a transformer and which size/type I needed. He was somewhat helpful and is also about to retire and is busier than he likely wants to be. He is my neighbor from up the road and typically comes over and helps me out with stuff periodically, but rarely charges me what he would clients because I typically do all the sourcing of parts and as much wiring as I can ahead of time. I try not to bother him more than is needed until I need him for some of the connections that I don’t feel qualified or experienced enough to do.