3phase230v motor 208 supply

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wirebender

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Just had an architectural firm ask me if I knew of an inexpensive way to fix a problem. Problem is a lift station with 5hp motors ($18,000)and someone screwed up and ordered 230v 3 phase motors but the supply is 208. Any fix for this without replacing motors?
 
Re: 3phase230v motor 208 supply

Buck boost transformers would be the cheapest way out I know of.

You would need just two buck boosts per 3 phase motor and for 5 HP these will be small and cheap.

IMO a better way to go would be a 208 to 230 3 phase transformer and install a 230 straight 3 phase panel just for the motors.
 
Re: 3phase230v motor 208 supply

Thanks, Bob. I mainly do churches and schools with a few houses thrown in and don't have any experience with buck boost transformers but I'm not planning on doing this job anyway. My brother works for this architectural firm and I just wanted to tell him some options to look at. This in San Antonio and I'm in Ft. Worth and don't think I want to drive 300 miles for this. Appreciate you taking the time to respond.
 
Re: 3phase230v motor 208 supply

The May 2004 EC&M Mabgazine has an excellent artical "Understanding Induction Motor Nameplate Information" written by Ed Cowren of Baldor Electric Co.
It is to be noted that motors should be able succesfully operate at +-10% of their name plate voltage. So 230v x 90%= 207v.
However, that most important issue is will the 208 voltage drop below 207v.
The type of loads that are driven must also be considered.
At 90% NP voltage starting and maximum torque may be down 19%, slip may increase 20-30%, FL efficiency down as much as 2%, at 3/4 and 1/2 load less than 1%, power fact up to as much as 7%, at 3/4 and FL, and up to 10% at 1/2 load, FLA up 5-10%, starting current down 10%, FL temp. rise down 10-15%. and maximimum OL capacity down 19%.
If it can be assured that the voltage be maintained at 207v and above you may be OK.
 
Re: 3phase230v motor 208 supply

I would not trust a system to remain at the nominal voltage, remember the utility can be 5% below nominal.

Use a boost transformer arrangement ("buck" means to lower)with a target voltage of 229V (10% boost) or 236V (13.3%). My choice is usually based on transformer availability.

Here is a link to a Square D BB Calculator.
 
Re: 3phase230v motor 208 supply

Thanks guys, I'll pass that on. Jim, that link didn't work for me, just got a blank page with a little square with a red x in the upper left corner.
 
Re: 3phase230v motor 208 supply

Using a full 3phase transformer will have to be rated the full 3.73 KVA of the motor. with two boost transformers the rule of thumb for 208 to 230/240 is for a 5 hp. put a dot before the 5 and this will be the KVA of the boost transformer. This will allow a .5 kva rating for a 5hp. But it does depend on the manufacture too so check with there web site Like www.squared.com. Do a search on buck/boost and you will turn up many sites. and wiring diagrams.
Whoops I was doing a single phase it would be 6.45KVA

I have done many lift station's and most around here is 120/208. The 120 is used for the control's and the cell link,and the GFCI receptacle, and the 208 will feed the pumps rated at 200 volts 3 phase most are between 3 to 10 hp. Did do one that was a 3 phase 480 delta but that was because of the long run back to the last power pole. there was a 480 to 120 transformer in the control cabinet for the 120 volt items and the 120 volt GFCI receptacle. One thing that perplex's me is only one came with a light in the cabinet. We had to install one in the all the others via inspectors request. And 210.70(A)(3)

[ June 18, 2004, 11:53 PM: Message edited by: hurk27 ]
 
Re: 3phase230v motor 208 supply

Wayne,
Your rule of thumb works only if you are using a 10% buck-boost (208->229). At 10% the required transformer is 1/10 the "normal" size.

Wirebender,
The square with a red X means your web browser is not set up to view the HTML format of the web page (might be because of the applets on the page).

To get to this page try this route: Squared.com - US - Support and Resources - Free Software - Select a Tool.

[ June 19, 2004, 09:54 AM: Message edited by: jim dungar ]
 
Re: 3phase230v motor 208 supply

Jim, thanks, reinstalled java and the link works fine now. The calculator seems a little slow responding though, is this normal? Again, I appreciate everyones input on this.
 
Re: 3phase230v motor 208 supply

Originally posted by wirebender:
One more question, Bob. What would be the downside of the buck boosts as compared to the 208 to 230 trans?
I have been told that buck boosts affect the power quality in the buildings electrical system.

Perhaps we can both learn if that is true or not from one of the other members here. :)
 
Re: 3phase230v motor 208 supply

B-B transformers just "tweak" the voltage and provide no isolation while a 208-230v transformer provides isolation by establishing a separate source, that is insulating and isolating the primary from the secondary from one another. (Please note that the insulating and isolating terminology which is commonly used to describe a 1:1 transformer should not be limited those transformers only.) This term refers to transformers where the primary and secondary windings are electrically insulated, that is separated and isolated from one another. These transformers can be modified with electrostatic shielding between the pri. and sec. windings which causes this noise to be transmitted to the shield by capacitive action, passing it to the ground which reduced the amount transmitted to the secondary.
Another issue is the size of the transformer required if using a B-B or an isolation transformer. You will find that if you don't need isolation that a B-B transformer a much much??less expensive way to go because the transformer kva size is based upon only that which is need to either buck or boost the voltage and not the entire load as an isolation transformer would be.
One other advantage of an isolating transformer is the most have primary taps, such a (2)2-1/2FCAN and (4)2-1/2FCBN, which can be used to correct the secondary voltage should the primary voltage be higher or, more commonly lower than the nominal voltage but it is never be misunderstood that it will regulate.
 
Re: 3phase230v motor 208 supply

Don't forget the "neutral shift" between the 208 and 230 side. There was a lively discussion about this a week or three ago in one of the forums. I dont remember which, but some guy took a beating for wanting to use an open delta. I also believe there is a good article about this on the Square D website.
 
Re: 3phase230v motor 208 supply

Whoops forgot to mention I use the open delta buck boost and if used properly it works well. Templdl gave a good explanation of the difference.
 
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