Phase converter voltage issues I THINK causing problems with new lathe. Please read!

Your interest and advice both greatly appreciated on this problem:

I picked up a lathe running a 7.5 hp spindle motor along with some low voltage ancillaries. In order to run the lathe in my rural shop, I installed a used ARCO HD7 rotary phase converter, which is rated at 15 horses starting, total load 30 horses.

Installed the RPC day before yesterday and took measurements, which I have posted below, and fired the unit up and then turned on the lathe. On occasion the lathe started roughly, kind of growling and then taking off and getting to speed. I am sorry I don't have a better way to describe it. At first I thought the electromagnetic brake was the problem, so eliminated it, and finally in the end I totally isolated the motor from the rest of the machine and still have the problem.

Now here is the where I need some help. We took some readings as per the ARCO website installation instructions and came up with the following. Phase refers to T1, T2 and T3, after the RPC. Phase 3 (T3) is the MANUFACTURED leg coming out of the RPC. The other two are from the grid. These are voltage readings.

Phase 1 to Ground: 124V
Phase 2 to Ground: 124V
Phase 3 to Ground: 240V

Phase 1 to Phase 2: 254V
Phase 1 to Phase 3: 253V
Phase 2 to Phase 3: 285V

Do any of these figures lead any of you to suspect that the power I am providing the motor would create the problem? The manufacturer of the RPC said that the 254/253/285 reading was not a big problem but to me the 124/124/240 seems a bit strange. Frankly, I am an engine guy, not a motor (electrics) guy. Any input that those of you who are well-versed could provide would be greatly appreciated.

Right now I am really appreciating my simple old Logan lathe, I can tell you that.

Thanks in advance.

Glenn

The voltage to ground means nothing as far as the motor is concerned, the motor, assuming it's 230V, is only concerned with phase to phase voltages. You are pretty high in that aspect, the motor will be at best designed for 230V, +10% makes it 253, you are right on the ragged edge of saturation, in which case your motor will run hot. If the motor is designed for 220V, you are over. The mfrd leg at 285V is just a meter reading from the capacitor in the RPC though, it's not "really" going to be 285V with the load on it, unless you took that reading when the motor was running. Did you? If so, that's a problem and might contribute to some of that roughness. A severe voltage imbalance makes the motor create what's called "negative sequence currents" that then create counter-rotating torque in the rotor, so the motor is essentially fighting itself a little bit to spin, which then means more heat in the rotor.

Other issues:
Are you sure the motor is strapped for 230V and not 460V?
How confident are you that the motor is good?
How confident are you that the RPC is good?

If any of the "ancillaries" are connected to anything but L1 and L2 that might be a problem as well.

I would just reiterate that make sure "ancillaries" are NOT on the generated leg as jraef said.
Rob

Firstly, Jraef and Rob F., thank you for your replies.

In answer to your queries, the motor OF THE RPC was running, but not the motor of the lathe when these readings were taken.

I pulled up the wiring diagram for the lathe and if I can will attach below.

As I stated earlier, I am no electrician, but as I read this I do indeed, assuming my electrician hooked up L1-T1, L2-T2, and L3-T3, have "ancillaries" being pulled from L3, the "manufactured" leg. These ancillaries consist run off of a transformer which provides 115V to the DRO and power to the disc brake, which has a rectifier converting 24V AC to 24V DC. Although I disconnected the brake and still had the problem I guess this could be the problem. If so, it appears to me that the best move would be to switch so that L3 feeds T2 and L2 feeds T3. Is this something that is OK to do? That is, do things get out of phase or whatever?

Thanks for your replies to this,


Glenn

I am not electrician either but do run off a RPC. I dont think the readings mean as much if only the RPC is running compared to when the lathe is running and the RPC has a load on it. If you are right and L3 (or L1) is the generated leg the yes it is a simple matter to switch it with L2. That will probably reverse the motor rotation though which you could correct at the motor OR then switch the new L1 & L3 with each other. In case you dont know, to change rotation direction on a 3 ph motor you just switch any two legs. In your case you would need to do that twice, once to get the generated leg where it will not mess with the electronics which reverses the motor, and secondly to switch the remaining legs to correct the rotation.
I hope this is a help. If your generated leg is not on L3 (or L1)
Rob

First thing I would do is reconnect the ancillaries to the solid legs. The voltage on the manufactured leg is unstable and depends on the load. You need to measure the voltages and currents while the motor is starting and running. Open circuit values are rather meaningless.

Tom

GBewley2 said:

View attachment 62662

Click to expand...

You do not want to connect your generated leg to L3 on the drawing. The reason is that L1 and L3 are connected to a control transformer.
Connect the generated leg to L2. Also you should try to use a few capacitors to balance your L1,L2,L3 from your RPC. Measure
the L1,L2,L3 voltages when the tool motor is running.

It also looks like you have a set of contactors for reversing the direction of rotation. If the forward/reverse switch makes the
motor operate backwards then just reverse the connections to L1 and L2 on the drawing.

You should also make sure that the transformer primary tap at 230 is connected. Just because the drawing shows it that way
does not mean that someone did not change it in the past.

GBewley :

A If you take picture from the motor nameplate and post here, the " diagnose " will be precise. Do it.

Take new voltage measurements between the phases ( phase converter running the 7.5HP ) and let us know. The voltages will be more pacified.
At this time, record the phases current with a clip on ampmeter. Let us know...

If you have another 3phase motor, connect it to the phase converter and check the voltage and current readings

Regards

Newton,

Which motor nameplate? Lathe or RPC?

Glenn

Newton said:

GBewley :

A If you take picture from the motor nameplate and post here, the " diagnose " will be precise. Do it.

Take new voltage measurements between the phases ( phase converter running the 7.5HP ) and let us know. The voltages will be more pacified.
At this time, record the phases current with a clip on ampmeter. Let us know...

If you have another 3phase motor, connect it to the phase converter and check the readings

Regards

Click to expand...

When the 7,5 Hp will be running together the Phase Converter the voltages will be more pacified. Take voltage reading and let us know.
At this time, take measurements of the motor currents, use a clip on ampmeter.
You may conect another 3 phase motor to the Phase Converter to evaluate the situation.
Please, thake a picture of the motor nameplate and post here.
The Converter manufactured phase as to be connected to the lathe phase L2, this way the anciliares are free of the Converter beavior.
The manufacturer comom practice is provide motor connetion to the highest voltage, check inside motor connection box.
Regards
Newton

I think Newton is wanting to be sure you are not trying to feed 220v to a machine wired 440v??
R

Rob F.

Rob F. said:

I think Newton is wanting to be sure you are not trying to feed 220v to a machine wired 440v??
R

Click to expand...

Thanks for help.

Yes, My concern is that the motor is connectd in 460 or 575V, and the supply is 230V. Twelve leads motor .

Thanks Glenn,,

The lathe motor nameplate will give lot of information re the motor and required power supply.

By the way, a picture of the nameplate of phase converter would be nice....

Edit: Glenn, I am new in this forum and not familiar with the " forum surfing" . I am affraid to lost the contact with you. If you do not get the answers for your questions, you may relay yourinfo to my email, [email protected].

regards

Some updates starting here. Firstly, some images that may be of use and which have been requested:

More images...the rest of the electrical schematics for the lathe.

OK, with those images posted, here is where I am:

I changed the connections around, at first swapping L2 and L3 from their respective places. Had to also swap L1 and L2 so that the motor didn't run backwards from the controls.

This improved start up dramatically, but two things happened, one of them a continuing problem.

Firstly, the spindle will still not come up to speed in it's top gear, which is 2240 RPM. No trouble at 1400, the next speed down. Of course, no problem for the motor to get to speed if the gearbox is in neutral. When in top gear, the motor doesn't get to speed quickly enough and contactors 1CR and 2CR are tripped.

I also seem to have lost power to the DRO. What's interesting is that the fuse 8FU is not installed in my machine although it was originally supposed to be there it would appear. Then again, the machine doesn't have the optional worklight, which was supposed to be fed by this fuse. Hopefully the fuse in the DRO has protected it.

So that is where we stand. A couple of notes...the motor is so buried in the machine I could not see the nameplate so had to just shove my smartphone in there and pray. Hope the pic is good enough. I also haven't been able to remove the connections cover on the motor to check it's wiring but have to ask if 230 would even make a motor wired for 380 or 460 run at all.

I am happy to take measurements with the motor running if anyone can tell me where to do this...I would prefer not to short the entire lathe out.

All additional help STILL appreciated.


Glenn

I would want to verify the wiring at the motor, just to eliminate the possibility....I think the motor may run at wrong voltage.
Is it cold in your shop and the oil in gearbox to thick to let it spin up fast? Can you heat the oil to test that, simple 100w bulb under it may be enough if overnight.
Are there adjustments on the control relays that set the overload rating? Usually a little dial.
If the transformer is wired for 230 it is a good bet the motor is as well.
Rob

My thoughts exactly on the transformer/motor situation, Rob. I'm liking your idea of adjusting the overload rating, although I'd be slow to do so without talking to Romi, who, btw, have been very helpful (tech guy named Clayton). If the oil is the problem, it seems to me everything is cut a bit too close...reminds me of a recent flight I was on where they asked two passengers to get off in order to be light enough for take-off. Yeah...well, let's not run quite that close to the bone!

GBewley2 said:

Some updates starting here. Firstly, some images that may be of use and which have been requested:

View attachment 62773View attachment 62774

Click to expand...

Did you take the cover off of the motor and verify what voltage it is jumpered for? I see you have 3 voltages to pick from... If you change from a high voltage to a low voltage and have a motor starter with heaters like an AB starter the heaters will be the wrong size and it will trip out until you provide the proper heaters.

John

OK, John...let me first make a statement to be sure I understand your question, then answer that and ask another.

If you mean the lathe motor, as I said I can't really get at it. Yes, it would be best to get in there and check, but this is essentially a new lathe from the factory and the handwritten tag an every other hint says it is set up for 230V. I really am not scoffing at your suggestion, I just don't have the means easily available to lift the motor out or the lathe off the motor.

Now...tell me about motor starters with heaters? I have no idea what you are speaking of. I do know that there is a tag atop the motor which says "Thermostat/Thermostato 130C" A photo of this is below, but as the contactors kicking out are on the lathe electrical panel, I do not think this has to do with the problem.

Then again, I'm a babe in the woods here.