Single Phase to Three Phase Converters

[jartgo]

I am working in the periphery of a project where a vendor supplying pumps to replace existing, is proposing to do so with three-phase pumps, where single phase pumps are existing. Since there is no possibility of three phase power being run to the site in this scenario, the vendor is proposing a "three phase transformer" to be provided with the control panel.

I had never heard of this but through google have learned a little about them. Seems a little odd, but I certainly haven't seen everything. I would like to see what you all think about the use of three phase converters and what their proper application/limitations are, particularly with respect to water/sewer industry.

I understand that the pumps are three-inch and considering that the existing pumps being single phase...I'd guess that these new pumps are 7.5 HP or less.

Unless the pumping conditions have changed, or the existing pumps just weren't getting the job done, it seems a bit confounding to me to propose a three phase converter, at this point.

Thanks in advance.

 

[waross]

There are lots of three phase transformers available in all sizes and voltages. Unfortunately, as the name may imply, a three phase transformer won't work well on single phase and won't develop three phase power from a single phase supply.
Look into the use of Variable Frequency Drives. There are quite a few available in the smaller sizes that will accept a single phase supply and output three phase power to a motor. Some models may need to be de-rated.

Bill
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"Why not the best?"
Jimmy Carter

 

[ScottyUK]

For any given rating 3-phase motors are cheaper, lighter, and more rugged than the single phase equivalent.

Personally I'm not really a fan of phase converters, never had much luck with them on the few occasions I've tried. In the size range you're looking at you can probably get a single phase VFD which will generate a synthesised 3-phase output, both allowing you to use 3-phase motors and also giving you variable speed control. There are a couple of caveats: 1) if you have a lot of these on one supply then you may find problems with harmonics which can affect other loads; 2) water, and especially waste-water, installations often have gases like H[sub]2[/sub]S which can attack metals used in electrical equipment. The problem is much more severe in electronic equipment such as a VFD unless measures are taken to mitigate it.


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If we learn from our mistakes I'm getting a great education!

 

[PersonalProfile]

Given we are talking about 7.5 hp why just just strongly suggest the supplier supplies single phase?

The solution may be different if they were say 10 or 100 times larger.

Regards,
Lyle

 

[jraef]

Lylebrown00,
In the wastewater industry, some of the largest suppliers of submersible pumps are European and only make them with three phase motors. The pumps must be certified by various agencies around the world for being explosion proof at great expense, so they do not offer single phase versions just to satisfy a relatively small portion of the North American market that has no three phase service. They make us deal with it at our end. So it's entirely possible that this vendor has no true single phase option.

Jartgo,
There is no such thing as a "single phase to three phase transformer" but your vendor may have been using that term inappropriately thinking you would not question it further, they get like that after spending a lot of time explaining this to people who usually don't care anyway. What they will give you is a single phase to three phase converter. You need to ask which type, each comes with it's own set of problems. I and others in here can tell you what you are in for, but I'm too lazy to type that much on my iPad keyboard. Find out what kind of converter they plan to offer and we can fill you in on what to expect, or maybe demand.



"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[MAGTiger]

A 15hp 3 phase VFD can be supplied from a single phase source then provide a 3 phase output to the motor at 7.5hp. This is a fairly common application. Should work well as long as you don;t need to change voltage.

Neil

 

[Skogsgurra]

There used to be rotary DC to three phase converters. They took DC via a commutator and made the rotor spin - very normal design. Then, and this is not seen everyday, they put three slip rings on the shaft and picked a three phase voltage from three evenly spaced bars on the commutator. I was asked to find the reason why one of this animals didn't work so well. I chose not to show my ignorance and fixed the brushes and commutator which were in a terrible shape. So, I'm the expert now

Robust machines that you may be able to build from an old DC motor. Just add slip rings and three connections to the commutator. Then feed your single phase supply via a rectifier and perhaps a starting resistor to the motor. Lean back and enjoy.

(There will probably be a few quirks along the rod, but this was done Before VFD and can probably be done again).

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[Motorwinder]

Even if you can get the pumps in single phase, 7½ hp single phase motors are pricey.

Here's a link for, in my opinion, is the best phase converter on the market.

http://www.phaseperfect.com/

 

[Skogsgurra]

Found these. Looks like they are still made!

http://www.americanrotary.com/products/phase-converters/rotary-phase-converters

Total surprise to me - but good for you

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.