# 3 phase convertion



## A Little Short (Nov 11, 2010)

inventor said:


> Hi
> I have a 3 phase electronic cooling unit for testing electronic components with 1/2 HP motor in it and I use GWM model # DP 256 3 phase converter to power it but the third leg from the converter is giving me 220V to the ground the other two legs measure 120V to the ground the manufacture is telling me that "Yes that is correct. In the phase converter world the manufactured leg is a “wild leg”. That being said the third leg should only be used by a motor on the load (never connected to any controls)".
> So the question is how to convert the 240v single phase power supply to a suitable 3 phase?
> 
> ...



If it's just one piece of equipment, you would probably be better off with a VFD.


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## CMP (Oct 30, 2019)

You need to examine the schematic/requirements of your cooling unit, to see if it is compatible with the phase converter output.


All rotary phase converters produce a center tapped delta output, with the wild leg.


Typically you would connect the load, so that the wild leg only powers the internal 3Φ motor. The remainder of the internal controls would only be powered from the 120/240V 1Φ legs, that supply the converter.


Powering the cooling unit from a VFD, may not be feasible, depending on what it's internal makeup is.



Since you can't yet post a photo, can you provide a link to a drawing of your cooling unit, so we can see what your working with ?


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## 460 Delta (May 9, 2018)

ONLY test voltage leg to leg, not to ground, this aggravates me to no end in MCC's and other places 3 phase exists and guys take their meter and check to ground.


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## paulengr (Oct 8, 2017)

460 Delta said:


> ONLY test voltage leg to leg, not to ground, this aggravates me to no end in MCC's and other places 3 phase exists and guys take their meter and check to ground.



That will get you in trouble. Many VFDs have MOVs wired line to ground with tighter voltage levels. Also industrial plants almost exclusively talk phase to phase voltages but utilities almost exclusively talk phase to neutral voltages.

ALSO it is a normal (standard) troubleshooting procedure to check voltage to neutral to find floating neutrals never mind ground faults on deltas. And it is a requirement to test before touching anything because you might have what appears to be zero volts phase to phase everywhere but the reality is only 2 of the three phases disconnected and the other two are floating so touching the remaining live phase is potentially deadly.

Plus is this a good idea on a wye wired three phase motor, especially if the wye is grounded which some are or is set up with differential relaying?

I agree that it is very useful to check the delta line to line voltages to make sure a three phase load is getting the correct (balanced) voltages but this is only half the picture and even on three phase delta-like loads it’s a bad idea.

Even on what appears to be a balanced 4 wire wye system I’ve had some surprises like when the utility had a blown BAY-O-NET primary fuse so we had “480” line to line but the regenerated phase was high impedance...essentially noise so no load would run on it. The only tell tale sign was the screwy line to ground voltages with a wild leg. The plant spent hours on it. I found it in 15 minutes. If I just measured line to line I never would have found it, especially because the utility didn’t even know the transformer had BAY-O-NET fuses. They kept checking the cutouts.


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## 460 Delta (May 9, 2018)

Paul, we aren’t talking about finding a bad/loose/high impendance neutral here, we are talking about the balance of a three phase circuits’s voltage. Phase to ground isn’t really relevant here. If you have a star system, or a grounded B delta, then a test to ground is somewhat relevant, but I have plants that are still on floating deltas so I don’t test to ground out of habit. When it is time for work on a MCC, I’ll test to ground eminently before work commences. 
I know you hate on solenoidal testers, but a K-60 Knopp would have found the ghost leg from the bad Bay O Net pretty fast.


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## tmessner (Apr 1, 2013)

https://www.phasetechnologies.com/phase-conversion These people make a digital converter that puts a "perfect" 3-phase wave form. It also consumes very little power when on there is no load.


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## inventor (Jul 22, 2012)

CMP said:


> You need to examine the schematic/requirements of your cooling unit, to see if it is compatible with the phase converter output.
> 
> 
> All rotary phase converters produce a center tapped delta output, with the wild leg.
> ...


Thanks CMP I will get the schematic for you


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## CMP (Oct 30, 2019)

tmessner said:


> https://www.phasetechnologies.com/phase-conversion These people make a digital converter that puts a "perfect" 3-phase wave form. It also consumes very little power when on there is no load.



The output of their converter is also a center tapped delta output, just like a rotary is. Clip from their manual.




> The three-phase output is delta configured. While the phase-to-phase voltages are equal, the phase-to-ground voltages are not equal. Phase-to-ground voltage for both T1 and T2 should be approximately 120V. Phase-to-ground for T3 should be approximately 208V. For three-phase loads that are designed for delta connection, the load derives its voltage phase-to-phase, so the phase-to-ground voltage should not affect the operation of the equipment.
> 
> If the connected load has a neutral connection and requires wye configured power, the output of the phase converter must be passed through a delta-to-wye isolation transformer before connection to the load.


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## tmessner (Apr 1, 2013)

Ok. point made. It still is a constant voltage, sine wave output. a rotary converter has a very unstable voltage and amperage output very dependent on the load applied. And it consumes a fair amount of power even in the standby mode.


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