Single Phase VS. Three Phase 4

[myancey]

I help design and build large Dairy Farms. Normally we use a 480 volt 3 Phase 4 wire system with a 400 amp Main. We've recently discovered that the utility company on one of our sites wants $130,000 to bring 3 Phase to the site. This is 3 times our normal expense and makes the use of 3 Phase prohibitive.

We have calculated the costs of converting the electrical loads to Single Phase 120/240 and this the most likely option from a cost perspective. Even with the additional cost of a phase converter for the one 40 HP centrifugal pump that will stay 3 Phase and additional expenses for single phase motors, the short term costs are still well below the $130K.

The question is what should be expected for long term expense as far as power consumption? Could the difference in efficiency over 5 - 10 years be enough to warrant spending the 130,000 now? And what factors need to be considered in that determination?

 

[busbar]

Could the extension fees be negotiated as part of a long-term power contract? Does the serving utility ever contract out poleline construction? Would the competitive bidding process be possible for the extension construction? Utility engineering fees are likely inescapable at any rate. (Deregulation spinoff?) Is future cost sharing of line-extension fees possible for ‘new customers’?

Compare 1ø motors vs. converter(s) and 3ø motors. Converters seem better suited for group-motor installations. Consider genset installation-/fuel-/maintenance-costs.

Take into account multiple converters–-milking period vs. 24-hr loads; i.e. refrigeration, well pump, water heating. High-current-density motors like submersible and hermetic-refrigeration motor warrantees may be affected if served via phase converters.

Factor:

Converter efficiency/losses (no-load and full-load) maintenance costs

Motor-starting voltage drop/power factor

For larger motors, current imbalance protection

Redundant converters and/or automatic alternator

If utility will not furnish single-phase service at 480V, would stepup transformer/smaller motor control be cost effective for larger motor(s)?

 

[BJC]

Check with the people who make VFDs ( veriable frequency drives) and softstarts ( Allen Bradley, Cutler Hammer, GE ,ABB etc). You need on that has single phase input and 3 phase output.
These divices have three parts- rectifier, DC bus and inverter. The rectifier inverts the DC into 3 phase output. It doen't care where the DC came from, it could come from 240 single phase, as well as a 3 phase 480 source.
I know Allen Bradley has these for small motors 10-15 HP but I am not sure how big they are available. The smaller ones are off the shelf and used for things like irrigation gate operators and fence gates.

 

[busbar]

myancey, when you have finsihed your design, I am sure there are readers here that be interested in your findings.

--busbar

 

[jbartos]

Suggestion/questions to the original posting marked by ///\\\:
We have calculated the costs of converting the electrical loads to Single Phase 120/240 and this the most likely option from a cost perspective. Even with the additional cost of a phase converter for the one 40 HP centrifugal pump that will stay 3 Phase
///Please, would you clarify what kind of existing service is to the dairy farm or what is the current situation. Normally, 40HP is relatively large load for 120V/240V, single phase, three wire, 60Hz power distribution system.\\ and additional expenses for single phase motors, the short term costs are still well below the $130K.
The question is what should be expected for long term expense as far as power consumption?
///There are more factors entering the scenario, namely, reliability of converters, life cycles, power quality motors are receiving, motor starting, etc.\\ Could the difference in efficiency over 5 - 10 years be enough to warrant spending the 130,000 now? And what factors need to be considered in that determination?
///The lower efficiency of the single-phase power distribution is just a portion of the concern. Other factors are maintenance and operation costs, life cycle of converters and motors, power quality motors are receiving, and any unforeseen additions/load growth that will require customization or converters.\\

 

[myancey]

busbar,

It seems that the utility company is, at this point, unlikely to offer any cost sharing solution. Aside from the deregulation issue there are some politics involved. These farms are far from popular and this particular utility company has not been very helpful as a result. There was another utility in the mix but they have backed out due to litigation problems with the first company I mentioned.

Contracting the pole/line construction has not been explored. That may be an alternative worth checking out.

As far as the use of mutiple converters, that option has been explored also. However, the vendors of the milking equipment normally supply farms that are serviced by single phase power. They are willing to convert the design to a single phase system with little increase in expense.

Therefore that leaves just one 3 phase load that cannot be converted, the 40 HP pump motor. I am presently contacting the vendor of that system to see if using a coverter will pose warranty problems.

From what I'm seeing so far it may. Other vendors we have contacted are refusing to warranty equipment supplied by a converter. That is a contributing factor to limiting it useage.

 

[myancey]

BJC,

We will be using a VFD on the vacuum pump system. ABB ACS 600 series. I looked at VFD's for other applications but the cost are prohibitive. It would be more cost effective to convert to single phase. ie fans, garage door openers.

 

[myancey]

jbartos,

The normal service we would install is a 400 amp 480v 3 Phase 4 wire system. Depending on the utility procedures they at times use a split neutral stepdown. We then would normally run a 75 KVA stepdown to supply 208/120.

Coverter reliabilty was a question we posed. I've found the reliability of converters to be fairly good from the sources I've checked. Most vendors offer a 5 year warranty on their converters.

Power quality however is an issue I've found little data on. Specifically, what effect will long term usage have upon the motor life. The load we intend to convert is a heavily used system designed to pump liquid manure.

I agree that increased operation and maintenance costs are a concern using single phase vs. three phase. However do you think they will outweigh $100K over a 10 year period? The 100K is what are estimating to be the short term savings after converting loads to single phase.

 

[busbar]

This might help a little…there was an article in the IEEE Power Engineering Review a while back about ‘written-pole motors’…for 1ø, up to ~60hp, IIRC. A google search shows some hits, with at least one pricing estimate.

(Like you mention, politics can be a big factor with utility policies but you’d think they would not have 3ø penalties for a >30hp connected load. Typical utility practice would prohibit 1ø service of that size. By “future cost sharing of line-extension fees” I meant that if, a new customer seeing the line is now 3ø and wanting service, would the utility reimburse your client for a portion of the $130k?)

One link that seems to have a lot of converter applications info is

http://www.gwm4-3phase.com

There’s surely others.

 

[busbar]

Pardon the blatantly obvious, but the NEC has a section devoted to phase converters –- Article 455.

Ironically, the 240V 1ø service-entrance breaker or switch, and maybe feeder overcurrent devices will likely only be available as 3-pole.

{What about a slick corporate sponsorship? If you could allow the phase-converter vendor to stretch the truth a bit, they could claim a $130K windfall by simply using their ‘very inexpensive’ products! ;-) }

 

[BJC]

Just curious.
How far out on the end of the line are you? Are you in an areas where wind snow etc. can take you out for a few days, weeks?
What are you doing for standby power? How many cows are there? How do you milk them when the powers off? Does Kelly girl have milkmaids?
There are some big dairy operations relocating near hear and they are using the methande to run generators. One group is going to build a ammonia plant using cow waste as feedstock.

 

[myancey]

I've actually thought about the "sponsorship" idea.... jokingly mentioned it to one vendor...not much response.

Article 455 on page 70-298 - 299 ....I'm very familiar with it.

Our normal vendor, Siemens, does make a Sentron Series MDP and main breaker in a two pole configuration the size we would need.

The lines are fairly reliable in this part of rural Ohio, although the winters get rough, lengthy power outages seem are few and far between.

This particular farm is a 800 cow dairy, small compared to the 36,000 head farm we just completed in western Indiana. There in lays part of the problem. Smaller dairy means smaller budget.

Backup power is provided by either a PTO driven or Deisel powered 150 KVA generator. Farmers choice.

BJC, I'd be interested in getting more info on the the methane powered generator you mentioned. Several of these farmers have inquired of these systems and we have toyed with incorporating it into our design. I know of one 2500 cow dairy in Wisconson that uses methane to power his entire farm, his residence, his herdsman house and sells on average $4000 of electricity a month back to the utility company.

If you could point me toward any info you know of...I'd appreciate it.

 

[BJC]

There were articals in the paper ( the Oregonian) here about the dairy and the methane plant. I think most engine manufactures ( Cat an Cummings for sure )make engines that run on metane. It's common at sewage treatment plants.
There are ads on TV here letting you know you can buy power made from cows.
Heres a link that mentions the dairy farm.

http://www.dairyfoods.com/articles/2001/0601/0601capital.htm

Columbia River cheese is part of Tillamook cheese. I think there was going to be something like 10,000 cows over there.
Here's another artical I found

http://www.dairycares.com/news/SJdairies.htm

If you do a google search on "Cow manure power" you'll get enough reading to keep you up all night.
Any reciprocating engine that burn methane is going to be big and expensive ( lots of piston displacement required to burn gaseous fuels).
I think the installation in eastern Oregon were almost force to utilze theire manure due to ecological concerns, It was cheaper than any other means of treatment.
If I see more on this I'll send you the links.

 

[busbar]

myancey, try a Google search on ‘biomass digester gas’

http://www.eren.doe.gov/power/repi.html

http://www.green-e.org/ipp/standard_for_marketers.html

I’m at busbar@@nikola.com

 

[jbartos]

Question: Could the 40HP pump be propelled by a diesel or gas engine?

 

[BJC]

Here is an artical that was in the paper here today.

http://oregonlive.com/science/orego...dard.xsl?/base/science/100203926225265348.xml

 

[jbartos]

Suggestion to the previous posting: The article may have overlooked the ecological aspects of farming. This means that rather than to burn potential fertilizers, it is better to return them to mother nature where they belong.

 

[don01]

hi myancey
my first comment from my end of the world is " they want how much to supply???????" It's no use to you but the fee to POS down under is only hundreds of dollars. you pay from the boundary.
Now I will make a couple of assumptions.
1) you won't use anything near 400Amp @ 480v ( 40 hp motor is biggest?)
2) you can get 1 ph to the installation at a sensible price?

There is an old fashioned device which may do the job and merge into your back up system neatly -the rotary converter.

Essentially this is a motor generator set. The speed will be basically mains controlled and coupling to other motor / methane eaters etc may be physically easier (peak load capacity).

Now keep a fair bit of single phase where you can and top up off the rotary converter(s) for the 3 phase (i would envisage a couple of sets)

This was how all the electric train and traction systems were done until the advent of easy 3 phase and reliable electronics.

Any way it sounded like a good idea.
please keep us informed and stick it to the power co.

regards Don

 

Have a look at our web site , this a common problem here in Australia & we have supplied many converters to this sort of application.

http://www.polyphaz.com

Regards
Peter Taylor