Newbie- What to do with a 460v 3-Phase Motor?

[Mrs.B]

First off, let me apologize for starting a new thread when there may be a discussion on this already.

We just got a 460 Volt 3 Phase engine lathe (geared head handle puller - not CNC). We are not nearly as ignorant about our power problem as we were when we bought this beautiful old machine. Where we are at now is trying to decide if there is going to be any way to hook her up without pulling the motor and taking it to somebody who we hope knows what he is doing. We tend to think that will be the inevitable next step.

The motor is single rated 460 volts 3-phase 11amps 7.5hp 1800 rpm. It is not dual rated and we can not find a wiring diagram anywhere. The motor has three wires coming out of it, and according to Auburn Armature Inc (whose sticker is on the newly rebuilt looking motor), they said if we had three phase 460 volts going in, we could just connect the power and it would be fine. Any thing else and we have problems to solve.

Question #1 Why 460 volts and not 480 volts?

We saw a phase converter that can take take our 220 volt single phase power and turn it into 415 volt 3-phase, such as the Eurotech. But as far as we know, that won't work. That is what they use in Europe and Australia. They are very expensive too.

Getting three phase power from the utility company's pole fifty feet away would be possible, but cost somewhere around $15,000 (we checked). That is not going to happen.

Getting 240 volt 3-phase seems to have several options under static, rotary and vfd. It seems we would still need some kind of brown out and/or phase fluctuation protection as well. We definitely prefer to somehow obtain balanced three phase power, or just buy a new 7.5hp 1800rpm single phase motor, but still have the problem of adapting the shaft to accept the spindle pulley belt drive. The latter may be the cheapest way to get the machine running, but more costly operating in the long run - motor life, Kw usage. We are not going to be running this thing all of the time anyway.

There are a couple of motor re-builders not too far from home. And they seem to be willing to venture to say that they can rewire it for 240 volt 3-phase and give ball park cost estimates between $600 and $750. Seems a little pricey to me. Together with a compatible phase converter, that might be the way to go.

Is there anyone out there who can confirm we need to pull the motor (it is huge and heavy) and take it to a motor re-builder to adapt it for 3 phase 240v operation? If so, how can we be sure it will be right when the motor plate clearly identifies it as 460 volt, not 480 volt? And finally, how would we decide on a reliable phase converter that would protect the motor and not break the bank? We really do not care if we end up with less than full horse power. But for speed and feed calculations, we do want to make sure it will run at 1800 rpm. (Question 3# what controls the motor rpm? )

Thank You,

Renee B

Ps. If we get this much done, will electricians be able to break out the wiring for the coolant pump motor without another big fuss.

[Al_The_Man]

The fact is that either way you are going to need a 1 phase to 3 phase convertor of some kind, my take would be to obtain a 220/240 volt motor or get the existing one rewired for 240v, if you are sure of someone who can do the job reliably.
This would mean obtaining a VFD that would be capable of running a 7.5hp 3 phase motor on 1 phase, many manufacturers limit their single phase operation to 5hp, some such as WEG I believe offer 1 phase for this size.
You show that you are in the US so the mains frequency is 60hz, a normal 4 pole induction motor cannot run exactly at synchronism or 1800rpm on 60hz due to something called slip frequency.
It will normally run at 1740rpm or thereabouts, unless it is not a normal induction motor which would be very unusual.
In any event, it is probably not going to be cheap.
Induction motor rpm is the freq of the supply, 60hz, x 60 seconds for rpm, divided by the number of pole pairs, in your case, 2. minus the slip frequency, which is 4%~7%.
A VFD would allow running exactly at 1800, or even double the input frequency up to 120Hz.
Al.

[cheetahcnc]

Get the single phase motor, modify the pulleys, and sell the 460 motor. A few things to look into: some 460v only machines have smaller gauge wiring and switching components (contactors, drum switches, control transformers) which are not rated for the amperage/voltage when going to 230v, and especially 230v single phase. If using a VFD, this is only for the main motor. Control circuits, etc. cannot be taken of the VFD.

Jim

[Al_The_Man]

Originally Posted by cheetahcnc If using a VFD, this is only for the main motor. Control circuits, etc. cannot be taken of the VFD. Jim

The OP states it is not CNC so I imagine there is not alot of control circuitry, nothing that cannot be taken care of with a 120v 1ph supply that is.
Al.

[lgalla]

Question for Al.
If replacing the 460 motor with 220 single phase,Will the 220V be much larger?
My shop has 575V3ph and 220single.Horsepower to horsepower the 575V motors are much smaller than the 220V motors.
Larry

[Al_The_Man]

Single phase motors are generally larger than their 3 phase counterparts, the difference between 3ph of the same HP generally depend on manufacturer and age of the motor, older 3ph motors tended to be larger.
Al.

[scudzuki]

I was facing a similar dilemma.
I have a Colchester Engine lathe wired for UK use (440v 50Hz).
I have a phase converter already (happens to be a phase perfect but for the sake of this discussion could be an RPC) so I have 230v 3 phase (actually 238v as my power from the utility runs a little high) which may answer one of your questions, US voltage is 115v/230v/460v.

Now my lathe has a 2 speed motor so replacing it would have limited the speed range of the machine.

My dilemma was, what if I put out significant $$$ for a step up transformer only to find that the motor is defective anyway (being as it has NEVER been run since it has landed on US soil) so I thought about testing it by tapping off the multi tap transformer in my VMC (which has taps at 380 415 440 and 480v) and it dawned on me what I need is a transformer out of an old CNC machine.

I found a 30kva transformer with 200, 220, 380, 415, 440, and 480v taps. My 238v into the 220v taps yields 442v out of the 415v taps. Relatively cheap, running at a fraction of its rated capacity, and versatile as hell. Something like this

3 PH CNC MACHINE POWER TRANSFORMER 15kVA | eBay

Joe

[Mrs.B]

Originally Posted by Al_The_Man Induction motor rpm is the freq of the supply, 60hz, x 60 seconds for rpm, divided by the number of pole pairs, in your case, 2. minus the slip frequency, which is 4%~7%. A VFD would allow running exactly at 1800, or even double the input frequency up to 120Hz. Al.

Thanks Al, your notes will go in the notebook for future reference

The dilemma remains up in the air. I will report what I find out about the single phase pump motor. Its identification plate clearly identifies it as an induction motor: The pump motor is rated at 60 Hz, 115 volt, 5.6 Amp; or 208/230 volt 2.8 Amp, Single Phase 1725 Rpm 1/4 Hp (seems that they accounted for the slip frequency you mentioned). There is some kind of box breaking off from the 460 volt three phase main input that I presume is designed to draw the single phase power down for the pump without imbalancing the 460 volts main 3 phase motor described previously.

The three switch boxes I have not yet opened (since I don't know what I would be looking for) are the on/off switch for each of the motors (on the operator's side of the machine). And thirdly, more curiously is the larger (about 4" x 8" x 12") box on the back side that seems to break out the single phase power for the pump motor.

With hourly rates for electricians being a factor in deciding what to do, we are leaning towards getting a phase converter plus a transformer that would hopefully provide the right kind of power that (presumably) can be easily connected to the only three wires that were clipped when this machine was taken out of the factory where it last ran. Call this plan "B" or "Joe's Plan" -scudzuki

Here is an interesting configuration that boosts the voltage before the phase conversion (for a variation on plan "B") I have not seen any other proposals to do it this way:
Adapters

We are still waiting (worried) for a price on this. It appears that their US distributor prefers to put the VFD in front of an AC transformer anyway. I do not know if that has to do with the way we distribute power in the US. I like the diagram shown on the previous link.

Back to our machine: It was running when it was sold from the shop floor, due to the entire factory being closed. The machine was purchased in "running condition". The main assumption is that the machine is OK as-is.

These are other assumptions:

1.) The single phase pump motor connections will not need any modifications if we use plan "B": a phase converter and transformer (or vice versa) to power the three phase input wires the same as they were when they were clipped at its previous home.

2.) The pump motor switch box somehow drew single phase power from the original three phase source without imbalancing the 3 phase power that then went on to the main spindle motor. Whether it was 120 or 208/220 doesn't matter because all of the wiring is already in place if we bring 460v 3-phase power to the only open wiring coming into the machine (is there a way to verify this?)

This is not the approach I said we were going to use in the original post. But, taking out the motor is no small chore. Then we still need to have it rewired correctly, put it back in, readjust the pulley belts, and still get a 240 volt vfd anyway.

Without doing the math, it would seem that getting the right kind of transformer in place to get 460v 3 phase power without touching the machine wiring would be easier and cheaper.

But, if it burns out the main motor, makes the electricity bill significantly higher, or causes some problem I have not considered, then would plan "A" still be better?

[Al_The_Man]

Originally Posted by Mrs.B I will report what I find out about the single phase pump motor. Its identification plate clearly identifies it as an induction motor: The pump motor is rated at 60 Hz, 115 volt, 5.6 Amp; or 208/230 volt 2.8 Amp, Single Phase 1725 Rpm 1/4 Hp . There is some kind of box breaking off from the 460 volt three phase main input that I presume is designed to draw the single phase power down for the pump without imbalancing the 460 volts main 3 phase motor described previously.

If the machine was fed from 460 3ph then I imagine that this would be a transformer to drop down to 230 for the 1 ph motor, You may want to look at putting this on a separate 240v circuit from your service, this would offload from some of the 460v.
I am not familiar with the adapters in your link but they appear that that may be a solution, but just for the spindle motor, not the whole machine, but if you wire the pump direct, it may not be a problem.
i.e. VFD for spindle only.
Al..