"They" say it will work fine . . .

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j_a_wolfe

Member
We have moved a piece of older equipment from another location that was powered from the grid at 240VAC. The new location has 480 VAC and the plan is to power the equipment via a 480VAC Delta to 208/120VAC wye general purpose transformer. Output of said transformer will be routed through a 3 phase load center. Although the engineer says there will be "no problem", I'm not getting warm and fuzzy. Will universal motors rated for 230VAC run properly (albeit slower) at 208VAC? I'm not sure why but I seem to remember something about phase angle issues between 208 VAC derived from 3 phase supply and "normal" 240 VAC single phase. I'm not well versed in proper use of transformers but something sounds fishy here. Can someone shed some light?
Thanx,
Jim
 

M_A_A

Member
Location
Western MA.
I would check to be sure the motor(s) spec plates have the 208v rating on them. A lot of older ones don't. If they do they will put out less horsepower at 208. If they are only rated for 230 or 240 I would say they won't fair well at 208. I believe they overheat and the insulation will break down. The dual voltage 208/240 motors are made to handle the strain and heat of lower voltage.

Also I would suggest that the transformer be sized properly for the load.
 

WIMaster

Senior Member
Location
Wisconsin
No load speed will be the same, Horsepower will be less. I might be concerned with motor life depending on the application.
Full load speed may be less due to increased slip due to the decrease in HP.
Will they work yes, will they work well???
What is the aplication?
 

iwire

Moderator
Staff member
Location
Massachusetts
I would voice my concerns on paper and if told it will be fine I would gladly wire it up.

If it works, or not, or let's smoke out will be the engineers issue. I try to avoid pissing contests at work.
 

iwire

Moderator
Staff member
Location
Massachusetts
For what it is worth we had the same issue with an old elevator in an upgraded building.

The engineers had us resupply it with 208 and it would not work with a full load of people. We had to change it to a dedicated 240 volt transformer.

It was a seven story building owned by an electrical engineering company. :p
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
No load speed will be the same, Horsepower will be less. I might be concerned with motor life depending on the application.
Full load speed may be less due to increased slip due to the decrease in HP.
Will they work yes, will they work well???
What is the aplication?
Parts of this I am reasonably sure of, from my old manuals and training. I remember the speed of an AC motor is dependent on the frequency, number of poles and slip. So no change there. Horsepower is less though? My recollection is that amperage is higher not that horsepower is lower. I don't remember exactly where the information comes from, but I thought that the way a motor was rated for 208/230 vs. straight 230 is that the winding wire is sized to carry the increaseed current required by the decreased amperage for the same work (horsepower, and wattage) output.

I had a motor manufacturer tell me that most motors made today (in the 90's) were already equipped with 208/230 capability whether stamped or not.

Someone much more educated on motor theory than me please clarify this.
 

Jljohnson

Senior Member
Location
Colorado
HP should remain unchanged but......
Amperage will increase, thus increasing the heat on the windings and shortening lifespan, by how much???? Not sure of that. Look at a 5 HP just for arguements sake to understand what happens with the undervoltage

5HP x 746 watts= 3730 watts
3730/(240 x 1.732)= 8.97 amps

3730/ (208 x 1.732)= 10.35 amps

Depending on the service factor of your motor, this may shorten the life considerably or not at all, best to consult the factory and get the scoop on the equipment direct from them or provide the nameplate rated voltage, in my opinion.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
The motor itself is one issue. It may be OK on 208, but as others have said, it may not be. If this involves a complete control system with the motor/equipment, you may run into other issues such as the control transformer will now put out 104 volts. If you go the transformer route to power the equipment at 240 volt, care must be taken on sizing to account for the inrush, especially if it is a high inertia load. All things to consider.
 

kwired

Electron manager
Location
NE Nebraska
When it is said the horsepower is less that means the motor will reach same operating temp at a lower hp output value.

Reality is the load still demands same amount of power and the motor will attempt to deliver it - but will do so at a higher current and will result in higher operating temperature. If the motor was not operating at/near full load values when it was connected to 240 volts it will probably be just fine operating on a 208 volt system. It will still draw more than it did at 240 volts though.

If your equipment involves heating elements they will have less output at a lower voltage. There again it depends on how closely the elements were sized to the demand of the application as far as how effective they will be when operating at 208 volts.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
We have moved a piece of older equipment from another location that was powered from the grid at 240VAC. The new location has 480 VAC and the plan is to power the equipment via a 480VAC Delta to 208/120VAC wye general purpose transformer. Output of said transformer will be routed through a 3 phase load center. Although the engineer says there will be "no problem", I'm not getting warm and fuzzy. Will universal motors rated for 230VAC run properly (albeit slower) at 208VAC? I'm not sure why but I seem to remember something about phase angle issues between 208 VAC derived from 3 phase supply and "normal" 240 VAC single phase. I'm not well versed in proper use of transformers but something sounds fishy here. Can someone shed some light?
Thanx,
Jim
Assumption: By "universal motors" you mean standard Design B induction motors.
Following discussion is limited to standard stuff - Design B induction motors

Adding to all of the good comments:
Yes, engineers are whiley, slippery sorts. I certainly would not trust anything one said in a blog conversation.

That aside, what you are discussing is operating 230V motors on 200V - yes, "200V". That is the standard winding voltage if one is planning on using on a 208V system.

Here is the basic model:
1. Induction motors have to run within their rated slip - generally 3% - 5%. Even if the voltage is lowered, the speed has to remain about the same.

2. The available torque drops linearly with the voltage.

3. If one wants the horsepower back up to nameplate, the current has to go up.

So, what happens if the voltage is dropped from 230V to 200V?
The motor will only produce 87% rated power at FLA. If the motor is not loaded over 87%, the application is as okay as it was before.

Supposing the motor was loaded to 100%. To make up the power the current has to go up - about 16%. And that puts the application just over the top of an sf 1.15 motor. Probably still okay, but the motors will run hot. My inclination would be to buy 200V rated spares.

If the motors are 1.0 SF, they will run hot enought to burm skin. They won't last. I'd be buying new or rewinding for 200V (and 1.15sf)

Now add in a change in ambient to from okay to hot - say 20C to 40C. This is a problem. Conventional wisdom says the motors will fail in 1/4 normal time. A twenty year motor will now last 5 years. It's an accounting decision as to replace, buy new spares now, buy new later.

:angel:
As for the phase angle change through the transformers - that's a problem. One has to make sure the Sympathetic Inrush Harmonizers are adjusted correctly, or the inrush current can easily trip the feeder CB. :huh:

ice
 

Mike01

Senior Member
Location
MidWest
Voltage drop

Voltage drop

That's provided the voltage is always 208V if you have voltage drop in the building possibly caused by a voltage fluxuation on the utility side you may see an even lower voltage. Even if the 230v motor is rated at a voltage of plus/minus 10 percent thats 207V (@-10%) if you allow for a building voltage drop of 5% that puts you at 197.6V(208V Bldg. voltage) not including any additional utility voltage conditions, so a 200V motor would be a better solution, however as others have stated send in the RFI to the engineer record the response and wire away......
 

Cmdr_Suds

Member
If you have to buy a new transformer, why don't you just buy a 480D to 240D transformer? they don't cost any more although they might take a bit longer to get.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Lots of good stuff said here, some not as good but I think only because of semantics. Everyone seems to grasp the concept, but a few statements seem to reflect what may be someone interpretting terminologies slightly differently.

But first off, you used the term "universal motors". Maybe this is your own semantics problem, but a "universal motor" is technically an AC/DC motor with brushes, basically the type you find in portable power tools like drills and circular saws or small appliances like vacuums and blenders. If you meant to use that term in this true sense, then it is a different issue than what most everyone has been assuming. Please clarify that seemingly minor point.
 

j_a_wolfe

Member
"Universal" motor

"Universal" motor

First of all, thanks for the input. Most of what was offered was where I was but it's good to have some consensus.

Secondly, the term "Universal Motor" was taken from the motor nameplate. Without doing further research, I believe this to be more of a marketing term rather than an accepted naming convention. There is no mention of any operating voltages other than 230VAC.

Third, The application is 4 fractional HP motors running as drivers for small, centrifugal circulation pumps. The decision was made to run them in the current configuration, being aware that their service life may be reduced and replace with more accurately specified motors when replacement becomes necessary. Application questions were noted and made a part of the installation notes so there should be no finger pointing down the road.

Item, the last, Voltage measurements were taken at various points to determine if this was the only area of concern. It seems that all control voltages and power voltages are nominal. I think this unit must have been setup similarly in a past life and they just missed the circulators.

Thanx,
Jim
 

iwire

Moderator
Staff member
Location
Massachusetts
Adding to all of the good comments:
Yes, engineers are whiley, slippery sorts. I certainly would not trust anything one said in a blog conversation.

To be clear, my comments about EEs had to do with work in their own building. It seemed that they just did not take their own building as seriously as their normal projects.

The firm is a large and professional engineering firm and I don't recall having such mistakes on jobs outside there building.

Just like ECs buildings are often hacked up wiring. :D
 

iwire

Moderator
Staff member
Location
Massachusetts
That is because they have to do their own building with leftover parts from other jobs.

The last large company I worked for had built their own building.

The 1200 amp switchgear was used and had duct tape covering the selector knob for the ammeter, It had a note not to use or it would trip the GFP main. :)
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
To be clear, my comments about EEs had to do with work in their own building. It seemed that they just did not take their own building as seriously as their normal projects.

The firm is a large and professional engineering firm and I don't recall having such mistakes on jobs outside there building.

Just like ECs buildings are often hacked up wiring. :D

And just like mechanics often drive crappy cars.
 
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