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European Electric Motor 380v 3 Phase Running Slow in USA

Wak

Plastic
Joined
Jul 8, 2021
Background: I have been dealing with a company in Turkey for some time. The last time I purchased small lathe machines the motors attached to them were 220v single phase. Over the years the motors (50hz) have gotten worse (slower rpm) probably due to the electric supply being 60hz. I had a licensed electrician do the wiring for them and spoke to him about this issue, he wasn't much help and didn't offer any solutions. This is not my field of work so I have been using them while they degrade with the passage of time. I intend to replace them soon with motors from the USA.

Current situaion: I needed more of the lathe machines so I spoke to them about the 220v 50hz motors not working well here. Their recommendation was to use 380v 3 phase motors and suggested I would not have a problem with the hertz if I went that route. I was hesitant but it's not easy talking to the company because they do not speak English and their translator doesn't always understand what I say. So, fast forward, I have the machines now and tried to get them running. The problem is that they run very slowly. I can stop the motor shaft from spinning with my bare hands. I have gotten in touch with the company and asked them for help on the matter. Due to the time difference, they will get back to me tomorrow. I also contacted the motor manufacturer for advice and I am waiting on that end as well. It took over a year for me to get these machines so the person I had hired to do the wiring is not immediately available either.

I am attaching pictures of the motor tag and the setup. If anyone can point me in the right direction, the help is appreciated. I am trying to better understand what the problem is. If it is out of my hand, I will wait for my electrician and the company to get back to me.
 

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You are in new jersey? And have a 3 phase motor as shown in the photo is connected for high voltage, which is nominally 480v 60hz or 400 volts 50hz for that motor. Delta voltages would be 230v 50hz or 277v 60hz

Your wall outlet shows 0.460 volts on the dmm.

I doubt you have 3 phase at that outlet but rather 120/240v.

Buy a vfd and connect the motor for low (delta) voltage
 
Thanks for replying and my bad. I have edited the first post to attach the proper voltage reading from line to line - it shows 210V. There are three lines with current and the fourth is the ground, line to neutral shows 120V.
 
Connect the motor for delta.

But you need more volts. 210v 60hz is pretty low and the motor will run hot if operated at more than half load.

You will have better luck with an american 9 wire 240/480v 60hz motor, than a 277/480v 6 wire motor on 208/120v service.

Personally i would use 3, 24v:120v transformers wired as auto transformers to boost your 208/120v to something more like 250v/144v.

200v 60hz motors do exist but are hars to find. They are intended for 208/120v operation.

Most american 240v/480v 9 wire motors say "useable at 208", some list higher temp rise and higher amps. Or they have a lower service factor for 208v.
 
Your 308V motor is currently wired for wye. That is the high voltage wiring. It gives compatibility to 380/220V power. You have 210/120V power.

Reconnect for 220V delta, as shown in the motor housing cast-in diagram.

That will be 220V compatible, and you will be 5% low.

The difference in Hz will cause an additional "lowness" (it would actually be compatible with 260V, so would be better with real 240V 60Hz). Will it "work"? I do not know.

You seem to have 208VAC nominal, which is one of those problematic USA things..... it does give 120V circuits, but just is not right for a 240V or, worse, a 260V compatible motor.

Overall, since I assume you are running these machines, not selling them on to end customers, the best solution is to boost the voltage as suggested, and re-connect the motors as shown for the lower voltage..
 
There are three lines with current and the fourth is the ground, line to neutral shows 120V.

Can you expand on this more? Which wires have 210v between them?

Based on your picture of the wiring coming into the box and what you said here, I have to guess that you maybe do not have 3 ph here but rather a 1ph 220v with a neutral (to get 120v).

I will also add that just because someone is a liscensed electrician does not mean they know anything about wiring up 3ph equipment. Most of them who wire up homes never do that type of work to learn anything about it. (this I know from experience)
 
my thoughts were a competent electrician that used 12/4 or 14/4 wire for a 3 phase circuit would have taped the white wire blue....
 
my thoughts were a competent electrician that used 12/4 or 14/4 wire for a 3 phase circuit would have taped the white wire blue....

and secondly,

it is possible that he doesn't have 3 phase.

but rather 2 legs of 208/120 Y. the white wire may have 0.46 volts to ground as originally photographed.
 
If you didn’t have 3 phase it would not turn at all, so let’s move off of that concept.

You have 208V (nominal) 3 phase power, very common here.

Motors create torque based on their design ratio of voltage and frequency, missing that ratio by more than +-10% affects the torque output capability of the motor and if the load doesn’t change, the result can be that the motor appears to run slower, but in reality it is also burning itself up.

So when you were getting 220V 50Hz single phase motors from them, the design ratio was 220/50 = 4.4 V/Hz. When you connect it here to a 208V 60Hz supply, the ratio is 3.47 V/Hz, far far too low. When the ratio is low like that, the peak torque capability of the motor, that which is used to accelerate it, drops at the SQUARE of the ratio difference. So you were at 3.47/4.4 = 79%, so your peak torque was .79 squared, meaning your motors were only capable of 62% of their rating. That then means that your 1/2HP motors were putting out less than 1/3 HP and probably failing to fully accelerate the lathe, which you were interpreting as “running too slow”. They were actually overloaded and would have tripped on OL (at best) or burned up eventually.

Your new situation is even worse. You now have a 380V 50Hz motor, 7.6 V/Hz, being fed with a 208V 60Hz supply, 3.47 V/Hz, so the difference is 3.47/7.6 = .46, so the peak torque is now .46 squared = 20% or rated, or from a HP standpoint your 1/2HP motor is now a 1/10HP motor. That’s why you can stop it with your hand, it’s like a sewing machine motor now.

The good news it though that the cure is simple. Instead of reconnecting the motor for 220V and trying to find an electrician savvy enough to set you up with a buck-boost transformer, simply get a very commonly available 208 to 480V three phase transformer and feed the motors with 480V 3 phase. 480V 3 phase has a V/Hz ratio of 8:1, close enough to the 7.6:1 design ratio (within 10%) to not matter to the motor. You will get full power, 20% faster speed.
 
If you didn’t have 3 phase it would not turn at all, so let’s move off of that concept.

if he connected his three phase motor to two legs of 208/120 thinking its 3 phase, it will generate torque and run, but not much.

if you draw the vectors out as 2 phase equivalent, he's got 208 on one phase and 60 volts on the other.

with three phase 208, the motor should have come up to full speed even with only 46% design voltage
 
If you didn’t have 3 phase it would not turn at all, so let’s move off of that concept.

It would not start the motor turning, but if anything else in the process is giving the motor some starting rotation it would indeed turn while single phasing. (as simple as OP fiddling around turning something while switching the electric)

He shows a picture of 3 Conductors entering a box (plus the bare copper ground to the box), and says that there are 4 wires. One is a ground, and then conflicting info states that there are 3 lines with current, but also a neutral that shows 120v between it and another line. That does not add up, and I think it is reasonable to want to clear that up before moving to more complex issues.
 
It would not start the motor turning, but if anything else in the process is giving the motor some starting rotation it would indeed turn while single phasing. (as simple as OP fiddling around turning something while switching the electric)

He shows a picture of 3 Conductors entering a box (plus the bare copper ground to the box), and says that there are 4 wires. One is a ground, and then conflicting info states that there are 3 lines with current, but also a neutral that shows 120v between it and another line. That does not add up, and I think it is reasonable to want to clear that up before moving to more complex issues.

I agree. The three wires and a ground, red, black and white appears to be a standard 240V single phase configuration in a residence.

The voltages on his wires also match for a 240v single phase outlet with issues. If he really has 208v 3ph, then he would likely have 4 wires and a ground, not that he would have to.
 
This is what i think OP has, and why his motor spins slowly.
2 legs of 208/120. Starting to be common in many appartment complexes.


20210709_124039.jpg
 
I appreciate all the input I am getting. Today has been a busy day and I could not sit down to give an update until now. Sorry for the confusion I am causing with my wording. I am a layman when it comes to this and I'll try to explain myself again (I might very well be explaining it wrong or misunderstanding what is happening).

First of all, I had been doing a bunch of reading before posting here and was leaning towards trying the delta connection but wasn't sure if it would harm the motor. Johansen saying to connect for delta gave me hope that the motor would be fine so I tried that and it worked! It was moving way faster. I have not been running the motors but for a brief period to check in case something is horribly wrong - I don't want to fry them. As JST, Jraef, and others have pointed out, it is still near 208v and not what the motor requires (255v) for this delta connection at 60hz per the motor tag.

As for the wiring, according to my understanding the three wires have 120v and the fourth is the ground. So wires A, B, C each have 120v. In the voltage picture, I am simply testing between A and B (210v). AC and BC also show 210v. A, B, or C to the fourth wire which is the ground (this is the confusion) shows 120v. I think I am calling the ground a neutral connection when there is no neutral. There are 4 holes in the outlet, 3 for the live wires and one that I will now call ground. Please correct me if I am wrong with the above but that appears to be 210v or 208v 3phase setup?

I like the simple cure, the easier the better. The past year has been tough. I had placed this order nearly a year and half ago and just got them now, business is hurting. I got 5 of these 3 phase machines, 2 are in one room and 3 are in another room. Is it better to buy a transformer for each room or just one at the electric panel? Can one transformer supply power to the different motors? All the motors are the same as the one in the original post. How powerful should the transformer be depending on how many are needed?


Lastly, for the 220v 50hz motors that have gotten slower over the past 5 years or so, would getting a transformer appropriate for them now bring them back to their former glory or are they in a sense ruined and it would be better replacing them entirely? They are still in use but the difference in speed is very noticeable.

Again, thank you for all the help and advice. You have offered more help than the people who sold these to me.
 
As for the wiring, according to my understanding the three wires have 120v and the fourth is the ground. So wires A, B, C each have 120v. In the voltage picture, I am simply testing between A and B (210v). AC and BC also show 210v. A, B, or C to the fourth wire which is the ground (this is the confusion) shows 120v. I think I am calling the ground a neutral connection when there is no neutral. There are 4 holes in the outlet, 3 for the live wires and one that I will now call ground. Please correct me if I am wrong with the above but that appears to be 210v or 208v 3phase setup?

Correct that is 208v 3ph. It was a bit confusing to me going off the picture and the wording in your previous post.
 
Actually, I like the idea of putting in a single 208-480V transformer, if you can find a suitable one, and leaving the existing connection of the motors. That avoids the re-connection, and is less hassle and less confusing than the boost transformer idea.

For rating the transformer, add up the currents for the motors you need to run at once. Multiply by the 480V.

The result will give the minimum "VA" rating of a suitable transformer. You may want to add some extra for any more machines you may want to add, to allow for expansion. It is wise to go a bit higher than minimum just on general, even if you do not plan expansion.
 
If you didn’t have 3 phase it would not turn at all, so let’s move off of that concept.

You have 208V (nominal) 3 phase power, very common here.

Motors create torque based on their design ratio of voltage and frequency, missing that ratio by more than +-10% affects the torque output capability of the motor and if the load doesn’t change, the result can be that the motor appears to run slower, but in reality it is also burning itself up.

So when you were getting 220V 50Hz single phase motors from them, the design ratio was 220/50 = 4.4 V/Hz. When you connect it here to a 208V 60Hz supply, the ratio is 3.47 V/Hz, far far too low. When the ratio is low like that, the peak torque capability of the motor, that which is used to accelerate it, drops at the SQUARE of the ratio difference. So you were at 3.47/4.4 = 79%, so your peak torque was .79 squared, meaning your motors were only capable of 62% of their rating. That then means that your 1/2HP motors were putting out less than 1/3 HP and probably failing to fully accelerate the lathe, which you were interpreting as “running too slow”. They were actually overloaded and would have tripped on OL (at best) or burned up eventually.

Your new situation is even worse. You now have a 380V 50Hz motor, 7.6 V/Hz, being fed with a 208V 60Hz supply, 3.47 V/Hz, so the difference is 3.47/7.6 = .46, so the peak torque is now .46 squared = 20% or rated, or from a HP standpoint your 1/2HP motor is now a 1/10HP motor. That’s why you can stop it with your hand, it’s like a sewing machine motor now.

The good news it though that the cure is simple. Instead of reconnecting the motor for 220V and trying to find an electrician savvy enough to set you up with a buck-boost transformer, simply get a very commonly available 208 to 480V three phase transformer and feed the motors with 480V 3 phase. 480V 3 phase has a V/Hz ratio of 8:1, close enough to the 7.6:1 design ratio (within 10%) to not matter to the motor. You will get full power, 20% faster speed.

Spot on...........
 








 
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