A decorative fountain at a shopping center has a 3 HP, 3 Phase, 208-240 volt pump.
The control box lists 10 amps for the motor.
The "factory test" sticker shows L1 @ 6.3amps and L2 & L3 @ 5.6 amps.

Since only single phase power is available, a Phase Converter (rotary) was installed.

The converter output voltages are all about equal (230-235 volts) but the pump draws 13 amps on L1 & L2 and 7 amps on L3, which is the "manufactured" phase.

Pump company says they "don't recommend" phase converters and tweaking of the vonverter capacitors may be necessary. Phase converter company says that since voltages are good, something may be wrong with the pump. They spoke to each other for me and decided that I should try adding a 22 mFD capacitor to help.

I think the darn thing should work as is.

BTW, changing the pump is not an option.

Any thoughts?

Thanks!

[This message has been edited by Redsy (edited 07-14-2006).]

Is changing just the pump MOTOR an option? Would be the simplest fix.

Why the differences in current draw between the 3 legs? Does the unit incorporate some control gear as well as the motor?

Get a new pump! I wouldn't want to instal this thing without GFI protection- and that motor is plenty small to be available in single phase.

BTW, there is no way a 3 hp pump pulls only 5 amps a leg. Look at your lift and flow- I bet you can get the same results with a 1/2 hp pump.

[This message has been edited by renosteinke (edited 07-14-2006).]

The whole thing is a brand new, unitized pump/fountain unit that floats in a retention basin.
It was specified and bought by the site manager, and installed in the pond by a different electrician. The phase converter was specified by an application salesperson, and installed by me.

I don't know why the current imbalance. The measurements are taken at the pump cable, and no other load is applied to the cable.

It's not a complicated installation. I believe it should work as installed, with equal current distribution.

[This message has been edited by Redsy (edited 07-14-2006).]

I suspect that the angle between the phases is different from the 120 degress that it should be.

Perhaps a VFD could be used to generate a good three-phase feed for it?

If you run the pump dry, under no load, then what is the reading?

Thanks for the input guys.

The unit is a UL Listed pump / aerator that comes as a package with a control cabinet, 3-phase GFCI and all the necessary controls. Replacement of components is not an option.

The converters troubleshooting guide suggests that the converter may need to be upsized, or capacitance added.

I think a mis-application has occurred.
If I was there initially, I would have insisted a single-phase unit be purchased.

I guess I'm headed to the "capacitor store".

A VFD was the answer, even if you neve change the speed. Most VFDs 3HP and uder can accept 1 phase input and give 3 phase output without derating. I think PRCs are a waste for anything 3HP and under.

Definitely looks like a Capacitive Reactance Tweek is needed here!

I bet the 22µF Capacitor brings the load levels on L1 and L2 down to the 10 - 11 Amps range, and the "Pseudo-Phase" L3 may drift around the 8 - 9 Amp level, which would mean it might actually start doing some work!!!

As it is now, only L1 and L2 are doing any work - L3 is kind of slacking off (insufficient KVA available).

With additional XC (Capacitive Reactance), the "Pseudo Phase" L3 can contribute more work, therefore bringing the polyphase loads more into a balance.

Just do not expect a completely balanced load value here!
The polyphase motor is being driven more from 1 phase apparent power, than polyphase apparent power.
The "Pseudo Phase" L3 does not follow the same power curves & all that silly E-lecktricul Injunearring type stuff, as the lines derived from the Transformer - and the real disappointing thing: they are still only a Single Phase!

This setup really should have been specified to use a 1 Phase 3 or 5 HP Motor - a Capacitor Start-Run type would have been a good choice too!

I realize the design and ordering of the pump equipment was in the hands of others, so maybe some "constructive critsism" should be delivered to the specifying party(s).

Something like:
"I feel sorry for that poor Motor, being subjected to that crappy power quality from the Phase Converter"


Scott35

See here:
http://www.aquamasterfountains.com/Pages/Classic-Home.html