Compressor 3 phase 230/460 volts

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Fordean said:
How would you continue. Please be detailed

Thank You Can you attached a model number. I can't return the unit they ordered it a while back. Why would they make 230 volts Its dual rated at 230 /460 but wired at the 230. Most know 208v are in the buildings. It this more European designed? Like to know why a 230 volt available. Mechanics order this stuff with no knowledge of power available. Motor say 7.5 HP 230volts 20 amps
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This has nothing to do with European equipment.
In the US, we build motors with nameplates showing the voltages they expect to see at their terminals after all of the voltage drop in the building wiring (this is called utilization voltage), while our building power systems use nominal voltages. This gives us motors with 230/460V nameplates intended for use on 240/480V systems.

The two values, 230V and 460V, come from simply being able to connect the motor windings in series or in parallel. It costs more to build a motor that can accept 3 voltages, so most manufacturers don't do it.

208V has been a common voltage for more than 60years, so there is no excuse for people ordering the wrong motors.
 
winnie said:
Assuming a pair of 2 KVA transformers to take 208V to 230V. This gives a load current of 75A, somewhere in the 25 or 30 Hp range.

Figure the transformers will have 5% core loss, running 24x7. So I estimate 200W * 8766 hours = 1750 kWh just to have the transformers present.

Figure the transformers will have another 10% copper loss when the load is on. So 400W * 12 * 6 * 50 = 400W * 3600 hours = 1440 kWh of losses when the transformers are loaded.

The load itself is assumed to be 24 kW, so 24 * 3600 = 86400 of real consumption.

So tacking the buck-boost transformer on adds 3.7% to energy use.

More realistically, the compressor won't be running full time during a shift. So the 1440 kWh of copper loss and the 86400 kWh of consumption both go down proportionally with run time. But the core loss is constant unless you put the transformers downstream of the control contactor (meaning the contactor has to deal with transformer inrush and higher current, not a good idea). Say the compressor runs 30% of the time...that core loss factor has now jumped to nearly a 7% energy use adder.

So IMHO the additional losses to using buck/boost transformers with the 'wrong' compressor are not huge in a relative sense, but also not insignificant.

-Jon
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Your loss values seem to be extremely high. I am used to see core losses of <.75% and conductor losses of <5%.

The buck boost transformer arrangement probably has much less in rush current than a full size isolation transformer, it should not present much of additional starting current, so switching it with the motor is not much of an issue, except for sizing the overload protection.
 
jim dungar said:
Your loss values seem to be extremely high. I am used to see core losses of <.75% and conductor losses of <5%.

The buck boost transformer arrangement probably has much less in rush current than a full size isolation transformer, it should not present much of additional starting current, so switching it with the motor is not much of an issue, except for sizing the overload protection.
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The 2 kVA was a WAG, based on an assumed motor size. We found out later it's only 7-1/2 HP. 22FLA nominal at 230V so the autotransformer is in the 0.5 kVA range. Negligible losses IMHO.
 
Fordean said:
Why would they make 230 volts Its dual rated at 230 /460 but wired at the 230. Most know 208v are in the buildings.
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They make 230V motors because it is trivial to design motors for full and half voltage. They target 460V in the design (for 480V systems) and 230V is a freebie.

If you want to keep the warranty, use buck/boost transformers. You would need a pair of 0.75 kVA units.

But I'd be inclined to go with @ptonsparky , give up on the warranty, run at 208V, and replace the motor when it dies. This is one of those 'out of spec but safe and will probably work' situations.

It might not work; if the compressor starts frequently and runs against the load (not properly sized, no 'unloading valve') then the motor will be heavily stressed. If the compressor runs infrequently and the plumbing is proper then the motor will run a bit less efficiently and a bit hotter than ideal.

There might also be problems with controls, either because of higher than expected current for dumb controls or lower than expected voltage for smart controls.

-Jon
 
jim dungar said:
Your loss values seem to be extremely high. I am used to see core losses of <.75% and conductor losses of <5%.

The buck boost transformer arrangement probably has much less in rush current than a full size isolation transformer, it should not present much of additional starting current, so switching it with the motor is not much of an issue, except for sizing the overload protection.
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I couldn't find good numbers on losses. Your loss numbers are in line for larger transformers, but transformer designs tend to get less efficient as they get smaller. On the other hand a b/b transformer is usually run at lower than design V/Hz, which will lower core losses.

Agreed on the lower inrush relative to total load.

-Jon
 
Bet it lasts a long time.

Neighbors irrigation well across the road from my house was converted from diesel to electric 10 years ago. The existing setup required 125 hp. POCO no longer allows across the line starting for anything over 100 HP. They decided they could change sprinkler package and make 100 HP work. I connected it up was drawing too much current, I told him he still had too much load and if I set overload as it should be it will be tripping every time he uses it, if I bump it up to where it will hold it will shorten life of the motor as it will be running too hot.

It ended up being bumped up to where it will hold. 10 years and it still is original motor on there. Been long enough ago I can't remember just how much overloaded it was, I kind of remember it was still within service factor amps though.

This thing only runs between May and September for the most part, but can be going nearly all the time in the hottest parts of the summer.

An air compressor may be used year around but unless there is high demand for air does probably cycle off quite often
 
winnie said:
I couldn't find good numbers on losses. Your loss numbers are in line for larger transformers, but transformer designs tend to get less efficient as they get smaller. On the other hand a b/b transformer is usually run at lower than design V/Hz, which will lower core losses.

Agreed on the lower inrush relative to total load.

-Jon
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My numbers were for transformers at least as small as 30kVA and prior to the latest DOE requirements.
 
ptonsparky said:
Google 'sizing buck boost transformers '
FPE has a link for sizing them. Opting for lower voltage output changes the size of the transformers.

I tried to paste the link but failed.
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I know Square D has an online calculator and so does Automation direct. Other transformer manufacturer/distributors likely do as well.
 
winnie said:
That is a job for proper labeling and documentation...and a problem with whomever ordered the wrong thing in the first place.
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If this organization practiced proper labeling & documentation, and effective internal communication, we wouldn't be having this discussion. We ain't 'zackly talkin' about an ISO 9000 facility here.
 
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