Compressor requires symmetrical 3-phase power?

Picked up a used Kaeser rotary screw air compressor. Was perusing the manual in anticipation of installing it. The manual says (paraphrasing): "The machine requires a symmetrical 3-phase power supply transformer with a WYE configuration output. Do NOT operate package on any unsymmetrical power supply."

We have 240V 3-phase high-leg delta in our shop -- clearly unsymmetrical. All of our heavy machinery (primarily older grinders of one type or another) operates very happily on this diet.

The compressor is a 208V 3-phase compressor.

My question is: Is this something that can be ignored, or are we seriously jeopardizing the health and life of this compressor by hooking it up to high-leg 3 phase? If so, are there VFDs that can convert high-leg to symmetrical? Don't want to throw a bunch of extra money at this used compressor, so trying to figure out if we should sell it and move on, or if there is some easy way to ignore or fix the problem.

Thanks in advance for any replies.

As long as your voltage and current are balanced the motor won't know the difference, unless of course it actually needs a neutral connection. (120v for controls or something?)

don't run it on 240v, get the buck boost transformers configured properly and run it on 208

johansen said:

As long as your voltage and current are balanced the motor won't know the difference, unless of course it actually needs a neutral connection. (120v for controls or something?)

don't run it on 240v, get the buck boost transformers configured properly and run it on 208

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Thanks for your reply. Questions (excuse the ignorance):

1."as long as voltage and current are balanced" -- Hmm. Do you mean the line to line voltage and current? Because each leg would have different voltage and current?
2. If run the three legs through a buck transformer, would the resulting feed legs out be equivalent in terms of voltage, or would there still be a high leg?

I would contact Kaeser and get their opinion, since you picked it up second hand I am guessing their are no warrantee AKA CYA on Kaesers end. So you might get a more honest answer from them. There also maybe a tolerance factor as well, for augments sake say +/- 0.05% wiggle room.
Do you know what type of motor is in the unit? Knowing that may give you some insight.
Let us know what you find out, I would be interested from an academic point.

I have contacted the manufacturer, but no word yet.

Have been looking into buck boost transformer options. What am I missing -- the ones I have been able to find are all about $1500+? That is almost as much as the compressor?

Check my math: (240v-208v)x28fla of compressor = .9KVA. I have been searching for "240V DELTA TO 208V WYE 3 PHASE TRANSFORMER", and only new ones show up, and they are expensive. Should I be looking for a VFD? Would they put out WYE configuration power?

This is why.............

VOLTAGE UNBALANCE (Electric Motor)

markz528 said:

This is why.............

VOLTAGE UNBALANCE (Electric Motor)

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At the risk of causing a holy war, why has high-leg delta been a mainstay of medium to smaller industrial shops in America for decades if voltage imbalance is an issue? All the electricians that I have spoken to say that 3-phase machines generally operate robustly on 240V delta?

Theoretically, why does this German motor in the compressor not like 3-phase high-leg, when, to my knowledge, all of the other 3-phase machines in our shop, and others, happily thrive on it?

Ther is really zero difference between a proper high leg system and an other 3 phase as far as the relation between the 3 phases are concerned.

However:

Some high leg systems are "open delta" and are not well balanced between legs.

And, because the grounded conductor (neutral) is on the center tap of one delta winding, the voltage to ground is higher on that leg. Something like a VFD, or other thing that has MOVs or other surge protectors, may be sensitive to the highest voltage to ground. In normal 240V 3 phase that is about 140VAC, but in high leg it can be over 200V.

Yup, many drives have jumper-screws that need to be removed to disable the line-to-ground MOVs and (sometimes) RF filters, if fed from an asymmetric or ungrounded supply. On some drives these are permanently connected.

If the drive has MOVs that kick in at 170VAC line-ground, there will be smoke if it's supplied with the 120/120/208 of a 240V high-leg system.

Palak said:

Theoretically, why does this German motor in the compressor not like 3-phase high-leg, when, to my knowledge, all of the other 3-phase machines in our shop, and others, happily thrive on it?

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My guess is that the compressor motor is sized razor thin built to IEC standards. It probably has very little wiggle room on performance because it is designed to use almost all of its hp on a continuous basis, therefore if the power supply is not well balanced the motor will easily overheat.

Your other NEMA motors are probably not running near full load amps during continuous duty, and even if they are, NEMA motors are a heck of a lot more beefy than an IEC motor and can take a lot more abuse.

markz528 said:

My guess is that the compressor motor is sized razor thin built to IEC standards. It probably has very little wiggle room on performance because it is designed to use almost all of its hp on a continuous basis, therefore if the power supply is not well balanced the motor will easily overheat.

Your other NEMA motors are probably not running near full load amps during continuous duty, and even if they are, NEMA motors are a heck of a lot more beefy than an IEC motor and can take a lot more abuse.

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Thanks for all the additional replies.

You are right -- for the grinders, most of their load, in my estimation, is during startup, especially with those running heavy wheels where there is considerable inertia when starting. Once they are spinning, I bet the amps fall to 20-40% of full load.

BTW, for future reference, I have found that we cannot use a buck transformer to go from 240V to 208V, because buck/boost transformers will not successfully effect a change from delta to wye power, which is required by the picky German compressor. We would have to install a full sized transformer.