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/s...+transformer#2

Southland sells new and used elec components.