Phase Converter question - 1ph to 3ph

[ExpatIreland]

I am in Ireland (230 v / 50 Hz). At my home shop I have single phase power. I'm buying a large coffee grinding machine with a 5.5 kW (7.5 hp), 3 phase motor . So obviously I need a phase converter. I am looking at a 7.5 kW rotary phase converter with a motor start capacity of 5.5 kW. Before I invest £8,000 in the converter and machine can you give me any tips on the best type of phase converter to buy and any questions I should be asking the manufacturer of both the machine and phase converter?

Also I am purchasing a weigh and fill machine for coffee bags from the U.S. It is standard 110 V / 60 Hz power. The motors on this machine are small, like 1/2 hp to run a small belt drive and a small air compressor. I have a 1 ph converter here in Ireland that is Input 230V / 50Hz and Output 110V / 50 Hz. Should I use this converter? Or should I put a frequency converter in-line that takes the power from 50 Hz to 60 Hz? Or should I buy 1 converter that is input 230V / 50Hz and Output 110V / 60 Hz?

Thanks in advance for your help and suggestions!

 

[edison123]

Wouldn't it be easier and cheaper to ask your utility to convert your supply to 3 phase, 4 wire system? Even if you spend that money on a converter (which is a complicated system for you to maintain), the power has to still come from your present single phase supply. Will your existing wiring take that kind of load amperage?

Muthu

http://www.edison.co.in

 

[ScottyUK]

For the grinder a VFD would work out a lot cheaper than the phase converter. OTOH that feels like a lot for a phase converter (too many zeros).

I like Edison's idea though - speak to the utility and see what a TP&N service would cost.

 

[waross]

Note re Standard US voltage. The standard voltages are multiples of 120 Volts (Plus the √3 related voltages of 208V, 277V and 347V)
Standard motor ratings are multiples of 115 Volts, 115V, 230V, 460V, 575V.
For the coffee machine; the cheapest will be to use an auto-transformer to drop the 230V to 115V. If the transformer has taps, set the output voltage as low as possible. The 115 Volt 60 Hz motor will only want 96 Volts at 50 Hz. Investigate the possibility of changing out the motor for a 50 Hz rated motor.
A 1/2 HP motor will be an induction motor. The motor will run at 5/6 of the rated speed.
Given the jump from 1/4 HP to 1/2 HP, 1/2 HP motors are often somewhat oversized. Consider changing a pulley to restore the speed to rated speed.
The compressor is an unknown. Compressors depend on inertia to carry them through the compression cycle. It will probably work on 50 Hz. If the compressor develops issues on the lower frequency, consider adding a (larger) fly wheel to the air compressor.
I agree with Scotty; VFD The DOL starting surge of the 7.5 HP motor may be over 150 Amps.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ExpatIreland]

Gentlemen, thank you very much for your comments. Here's what I can tell you . . .

On the suggestion of bringing in 3ph power that is not in the cards on several levels. (Remember, this is Ireland) -- The closest 3ph power (I am told) is about 1.5 km down the road from me, so you can imagine what the electric company is going to charge to bring it to me. Also, as soon as the county council gets wind of someone needing 3ph power they are going to want to swoop down and stick their nose in my business AND give me an annually recurring tax bill because I run a business out of my home. The last space I was in, which was similar in size to my current workshop, cost me about 60 quid a month just for the joy of supporting the county council.

The converter portion of my spend, by the way, is around £1.5k. Not a cheap piece of kit but much less expensive than bringing in power and much, much, much less headache than getting the county council involved. Besides them charging me 'rates', once I apply to get 3ph power the electric company will want to know if I have planning permission and then to get that I've got to go hat-in-hand to the local council and . . . well I think you can see where all this is going. On top of that I rent my space from an absentee landlord living in Australia so to get all these disparate people to agree and see things my way will be a tall order to fill. I figure that if I went that route it would be late 2019 before I got 3ph power. And I'd have a huge bill from the electric company. And I'd have a yearly tax bill from the council and nothing in return for the privilege of paying the bill. And no doubt I'd move premises soon thereafter just to try and lower my high blood pressure caused by the intervention of all these 'helpers'.

As to my home, mains power is 60+V. The main breaker is 63V. The 3ph converter specifications ask for 60V and run the power to the converter with a 10mm line. The local electrician says he can put a 60A box in and we can run the wire to my workshop, less than 10 meters from 60V circuit to end point, where I can plug in the converter.

On the VFD suggestion I will look into that for the coffee weigh/fill machine. That could give me the exact power the equipment asks for and save me from problems down the road.

Thanks again for your input and suggestions!

 

[jraef]

So if you go the route of a VFD, you will need to buy one that is twice the size of the motor at a minimum, so a 15HP VFD. The reasons are lengthy and you have to understand power conversion, but trust me, this is what all of the VFD manufacturers will tell you.

In addition, the output of the VFD cannot be used for ANYTHING other than the induction motor in your grinder. So if the grinder has a control panel, and inside of that control panel they tap off of the incoming line conductors to power controls and electronics, you cannot tap off of the VFD output. That then means you (or your electrician) must have the skill set necessary to properly identify and separate these circuits, then feed the controls with your "real" 230V power and have the VFD feed ONLY the motor. In addition, if there is already some means of turning the motor on and off now, which is a same assumption, then interfacing that with the VFD is also something that must be done carefully or you could damage the VFD. No offense intended but given that you had to ask this question and that you refer to your power as 63V / 60V, not 63 or 60A, I'd venture to say you are going to be relying on the electrician very heavily for this and if he didn't already bring it up, that points to his not being qualified either. Learning curves with VFDs can be very costly...

So one positive aspect of the Rotary Phase Converter is that from a standpoint of usability, it's a bit simpler to implement. You do still have to make sure your controls are tapped off of the "real" legs of 230V power, but that's just a matter of moving the phases to the right place. After that, everything else remains the same. Most decent electricians can handle that.

As waross said, the 115V motors will run slower and likely warmer, but should be fine for the reasons he stated. But when they do die, replace them with local motors.




" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[waross]

Consider changing the motors for 50 Hz motors. You may be able to use a 5 HP motor for the grinder and drop the grinder speed with pulleys if it is a belt drive.
Better informaion yeilds better answers.
Our answer are based on some assumptions because we don't have the full picture.
If you post the make and model numbers of the equipment that you intend to use we may be able to give you better advice.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[TugboatEng]

Even if changing the motor to 50hz a rotary phase converter is still required. The voltage really shouldn't be an issue. All of the Baldor motors I buy in that horsepower range are rated to operate on 208-240 volts (somebody at my company managed to special order a pair of 208v only motors for a 480 volt boat hut those are a rare breed). If you're not operating in high ambient temperature conditions or running above the full load rating of the motor you can fudge the voltages a bit. The static phase converter or VFD seems like the way to go here. Transformers are cheap to run the lower voltage components.

 

[waross]

Some of the motors are single phase, Tug.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[zlatkodo]

Regarding the 5,5 kW motor.
Why not to try with the most primitive and cheapest method:
connecting a three-phase motor to a single-phase network using a heap of capacitors (especially if the three-phase motor is designed to work in the Wye connection)?

 

[ExpatIreland]

Jraef, no offence taken. None at all! You hit the nail on the head, I am going to be relying on the electrician. And that is just it, a single person -- my electrician -- usually has one way of doing something but here, with multiple minds at work, I can see several ways of doing something and then decide on the best approach given circumstances, budget, etc. So I really appreciate EVERYONE's feedback. I'll talk with my electrician and see how familiar he is, and how comfortable he is with the VFD solution. As to 'using a heap of capacitors' I don't know, although I appreciate your out-of-the-box thinking. If I was the electrician and could figure the multiple capacitor system out and maintain it then I could see myself pursuing it -- I like cheap -- but since the machinery I'm using constitute my livelihood I'm going to lean toward the conventional, or more conventional solution.

 

[jraef]

The "heap of capacitors" method means having to de-rate the motor capacity or risk it overheating. So if your 5.5kW motor only needed to be 3kW that would be fine, but if that were the case, the OEM likely would have used a 3kW rated motor to begin with.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[zlatkodo]

The method I mentioned is not unconventional. It has been known in theory and practice for more than 100 years. This is so-called Steinmatz connection. The best outcome is if the three-phase motor is designed to work in Wye-connection .
Of course, this is not technically the best solution.
As you already know the best solution is genuine three-phase power supply .
As for overheating, it can be reduced by the correct choice of capacitance (depending on the load), as well as with additional external cooling of the motor.
Another option could be to redesign / rewind motor to single-phase winding, if you have a reliable service center nearby.

Tech Support in Motor Repair and Winding Design

 

[waross]

I'm always up to learn something new.
We have had at least one discussion as to whether it is possible to determine if a motor is connected in wye or in delta by electrical testing of the three line leads. The consensus was that it is not possible.
Is there a way to use capacitors to determine if a motor is wye or delta, having access to the three supply leads only?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[zlatkodo]

It is very likely that 50 Hz motor has 6 leads out .

 

[waross]

I agree that the motor will likely have 6 leads, however;
The available voltage is 230 Volts. It is unlikely that the motor will be rated for 133:230 Volts.
It is a safe assumption that the motor will be used with a delta connection.
Is there a version of the Steinmetz connection that uses the wye point?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Hi Bill,

Star-connected machines are pretty common in small sizes - below about 5.5kW or so - which gives options of either 400 or 230V. Above 5.5kW a delta connection is more common, giving options of 400V or 690V. It is certainly possible to obtain star-connected machines for 400/230V in larger sizes, but they aren't the default offering. I've always assumed this is because the delta winding is easier to manufacture because the conductors are smaller for a given power output, but I could be wrong.

ExpatIreland - any chance of a photo of the maker's plate on the motor? That might end the speculation.

 

[waross]

Thanks Scotty. The point is, with 230 Volts available, I doubt that the motor will be wye at 230 volts.
I am wondering why a star connection works better with a Steinmetz connection.
My thoughts were that a delta connection would see rated voltage across one phase and no shift in the angle on that phase.
The capacitors would "Pull out" the delta. Once the motor is up to speed, the back EMF will be close to the correct hase angles for three phase. Any current not supplied to the second and third phase windings by the capacitors would would be supplied by the back EMF.
I thought that the pase angles with a wye connected motor on a Steinmetz connection may be less well defined.
But I may be wrong.
Is there any reason why more capacitors may not be used to increase starting torque if they are cut out of the circuit as the motor comes up to speed?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Oh right, I see your point now Bill. Yes, agreed - it won't be a 230V star connection.

Intuitively, and at this point I admit that I haven't tried to analyse properly, it feels like the star-connected winding works better in a Steinmetz connection because the capacitor is in series with a single winding, not the common point of two windings where the capacitor carries the vector sum of the two winding currents. With a star connection the capacitor produces a near-90° shift in the current for the single winding; I'm less certain what the phase shifts would be in the two windings of a delta-connected motor.

Perhaps someone feels like sketching the vector diagram out... right now I'm more concerned with where my next beer is coming from! Cheers folks.

 

[waross]

Thank you for that insight Scotty.
As to the phase shift for a delta:
Draw the vectors vertically.
When you apply single phase current across one phase (A-B), the other two phases are in series and at the same angle.
The capacitor is connected to C and pulls the windings to the right to form an isosceles triangle.
The displacement is at 90 degrees to the supply voltage.
I think.
There may be some vector similarities to the Scott, Fortescue and other connections used to convert between two phase and three phase, and with the three phase "T" transformer.

Bill
--------------------
"Why not the best?"
Jimmy Carter