3 phase

Is 3 phase power available to a residential electric utility customer, or to a small shop? Is it prohibitively expensive to have installed (brought to the meter, that is) or to pay for on an ongoing basis? If you had 3 phase power to a shop could you use one leg of it and a neutral for 120V circuits, 2 legs for 240V circuits? Or would you need to have separate single phase service?

What about workarounds like a phase converter, or using a motor to provide a third phase? Difficult, expensive, dangerous, more trouble than it's worth?

Thanks in advance, Stan

If I was going to buy one book on electricity it would be;

Moderen Refrigeration
Goodhart & Wilcox
ISBN 0-87006-642-0
About $50.

This one book has the best explantion of basic to advanced electricity and how to apply that knowledge to many different applications.

The way the info is presented, it's very easy to understand. Alot of therory will not make any sense at first from any text but if you just believe what your reading, you will soon realize what they were trying to teach you, will be explained latter on in practical experience.

T_Bone

I especially like your comment about ".....how to apply it". In coming up thru the educational system, early on, I had no idea what you did with all the stuff they were trying to teach me.

Had they subscribed to what you said, I may have been more interested (gee I'm gonna need this stuff so I'd better learn it) and my education would have gone much smoother.

Mark

Ya I had a real hard time trying to comperhend all the info at first as I kept asking why. I then made up my mind just to believe everything I was being taught as I would find out why at a latter time.

With my new AA (attitude adjustment) I found out I moved quickly ahead and it was actually enjoyable to be able to use what I had learned. The first couple years I kept saying "oh that's why they said to do it that way"

T_Bone

My problem was that I didn't want to do it (schoolwork) and needed some motivation and had they told me that it may have provided some motivation that was sorely needed. But it worked out ok after all and I agree; putting to use what you had learned and seeing things work like you had predicted is really cool.

Mark

You would think that they would do it for free with all the power we were going to need, but na-da.

For a farm shop I doubt you'll get it free.

Mark

• 3 phase converter

The phase-to-neutral voltage is 120, so 120 volt equipment is fine connected to one leg of a three-phase service.

Three-phase power is normally used in shops that have a lot of rotating equipment (lathes, mills, drill presses, etc.). Three-phase power does not suffer the 120 cycle per second power fluctuation of single phase power, which translates to much less vibration.

Interesting what you said in your last paragraph. Explains why a 1/2 hp drill press would be on 3 phase. Makes sense.

We used 400Hz 3 phase in our electronic equipment. Not because of the power consumption, but like the precision machines, it was smoother and for us, easier to rectify and filter into DC and when weight and space are issues, that is important.

Mark

It sounds like you've worked on military aircraft. I think the use of 400 Hz 3-phase in aircraft is driven by the need to generate the various reference voltages used by synchro repeaters. Of course, the availability of three-phase makes it possible to have small, powerful AC motors, very desirable in an aircraft. (Since three-phase motors require no starting circuits, unlike their single-phase counterparts, three-phase motors can be quite compact.)

Just a bit of trivia: Multi-phase power was invented by Nikola Tesla before the turn of the century. Had Tesla (or someone else) not invented it, it's likely that today we would be using DC power exclusively! Tesla licensed his patent to George Westinghouse, but when the royalties exceeded what even Westinghouse could afford, Tesla signed over his rights to Westinghouse for free. So Tesla earned almost nothing for his invention that is the backbone of the world's power distribution.

Stan

If you google on "tesla", you'll find all sorts of bizarre anecdotes on this subject. Wireless transmission of power was one of his dreams; while Marconi saw the use of radio waves for communication, Tesla saw them as a conduit for power transmission. As I recall, he thought he could bounce power off the ionosphere to deliver it around the world. (I don't think he thought about how to meter it, though!)

Tesla experimented with wireless power transmission for years. Eventually one of his experiments melted down the Colorado Springs municipal light plant; that was pretty much the end of his experiments as he was run out of town.

Course the sun does it all the time and it's obvious how ineffecient it is. (How big a solar cell do you need just to power an intermittently used gate opener.) Only difference between the sun and Tesla are the frequencies...and distance.

Mark

On the AC-DC thing, I heard that the folks trying to ship power across country learned early on that they could ship ac much easier and I am assuming that they were referring to the ability to run it through transformers, thus stepping it up to ungodly high voltages, with minimum I squared R losses and away they went.

Case in point on ac benefits. Local Rual coop had distribution problems. Had too many customers for the service.

Real simple solution. Doubled the voltage (7kv to 14 kv). All they had to do was put a 2 disc insulator on each pole rather than a single, and install a (new) transformer with half the turns ratio at each customer's house. Real fast and some of the (old) transformers were really old and probably needed to be changed out anyway. New customers needed a transformer anyway so they got the new ones. Slick!

Mark

Yep, the advantage of AC is the ability to easily transform to higher voltages for distribution. However, without multi-phase power, this advantage was moot because you can't build a big enough single phase generator to generate significant power without serious vibration problems. Tesla's invention of multi-phase power made ac power generation practical. Even after Tesla and Westinghouse demonstrated the superiority of ac power, Thomas Edison fought vigorously to discredit ac. Edison so far as to build an ac electric chair to prove how "dangerous" ac power was. (The electric chair was a failure: instead of instantly killing the condemned man, it slowly incinerated him.)

Today, interestingly enough, when power companies need to deliver power over very long distances (>200 miles, I think), they will often use DC transmission lines, converting ac to dc and back using large generator-motor sets. It turns out that dc doesn't have as much loss over a transmission line as ac, so it makes sense to use high-voltage dc in some cases.

Back in the 70's I lived in Denver and not far from the house was a small transmission building. From what little info I could gather, they were experimenting with microwaving electricity to NY City.

I stopped in to get more info but was promptly showed the front gate. lol

T_Bone

Check out the link below, to the Practical Machinist BBS covering phase conversion and VFD's:

I'm VERY lucky to have 3-phase at my farm shop, and have been able to get some bargains on 3-phase stuff. A neighbor (now deceased) had a Certified Seed cleaning plant on his farm, and no three-phase. He ran the cleaning mills and elevator legs for many years on a rotary phase convertor with no problems.

• Power IT UP

To install it, you indeed would need a special, very expensive circuit panel and breakers. In addition, you would need a single phase panel for ordinary circuits.

I have a friend who is a long ago retired Eastern Airline Pilot. He built a southern mansion like house (that would make Tara in Gone With the Wind look small) and had three phase run to the house to power the air conditioners and a few other items. An expensive way to go in the 1970's (or late '60's, I'm not sure which) and in todays dollars, it isn't worth it.

Businesses such as convience stores and fast food places can use three phase as they have lots of coolers and other equipment that use three phase. They also can use two of the legs, 277V for flourescent lighting, saving them big $ in the long run on electric service and operating costs, and equipment purchases (no motor starting condensors or other problems on three phase)

As noted, normal, single phase welders are not that expensive a proposition.

Charles

As far as a converter, on a welder you are talking about serious current. A converter will run a 1/2 hp lathe or something like that ok, but to get one big enough to supply a 200a welder you are going to pay some bucks.

My last stick welder purchase was a 200amp AC-DC and was a 230 volt Miller brand. Bought it from the local welding materials supplier. Cost was about $250 in 1995 dollars. Made to order, made for the farm and made to run on available juice.

You aren't going to get there fooling with that stuff on ebay.

My 2C

Mark