phase converter questions

On Tue, 31 Aug 2004 07:11:31 -0700, Eric R Snow vaguely proposed a theory ......and in reply I say!:

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Haha! _Building_ one is actually probably not illegal. I mis-worded!

But no, I could not hook it up, unless it had a plug to plug in, and a socket to take out. I cannot wire it in.

I realise it _may_ be hard to tell who did what, if it's a bought one. But a home-built one one would be a little easier to spot, even if well done. If anyone in control was suspicious, they could ask me to prove installation by a electrician.

Interesting about the search warrant. Firstly, if I had any work done by an electrician, he has to submit a "ticket" to say it's done. It can be inspected. He may also report what he sees, of course.

A story. A little while back, I was in a situation where my bush-pig neighbour was stealing water from my dam (he set fire to the place while he was doing it), and repeatedly dumping his household rubbish on my property. I reported this to the police, who took no action, and the Council, who sent the Health inspector out, accompanied by police. He had more powers of entry and search than the police. They were there to provide muscle, and to arrest the guy if he tried to stop the inspector. So he and other statutory folk often have more power than police!

I really think you ought to put one together and see if it works for you. Since your limit is power available, let me tell you of one I put together. It was for a fishing rod blank company that had a centerless sander. This was about twenty five years ago so I may remember somethings incorrectly. But I think the main motor on the sander was a 5 hp three phase motor. I used a 7.5 hp three phase motor and a two hp single phase motor with a belt drive between the two. I forget the size of the breaker, but it was just big enough after some fiddling. The pulleys were adjusted until the current drawn by the single phase motor was about 85 to 90 % of the name plate current. Some capacitors were connected between one of the hot legs to the leg not connected to facility power. As I remember the current drawn by the single phase motor decreased as caps were added and then started to go back up. So some caps were removed so current was a minimum. Then some caps were added across the power line for power factor correction. I never try to completely correct for power factor. If you plot current as you add pf caps, you will see the first one drops the current a good deal, the second one drops it less. The third one even less. And remember that power factor correction only decreases the imaginary current. The real current varies with the load. The imaginary current does not vary with load. But for your case where you are current limited, reducing the current when unloaded, will cut the heating of the breaker and wires when you are not loading the output. And helps keep the breaker from blowing. Anyway I played around with caps of a couple of hours, and the guy used it for over twenty years ( But only used the sander maybe every ten days, it was not 8 hours a day 5 days a week ).

One thing to remember about RPC is that they are only generating the current and voltage for the third leg. So if you can get two thirds of the power out of a three phase motor running it on single phase power, you only need to generate one third of what a three phase generator would have to generate.

Dan

Old Nick wrote in message news:...

Actually the power factor correction does not change at all with load. Changing the load only changes the real power and the power factor caps only change the imaginary current. The effects of power factor are much more obvious at no load, so do power factor correction at no load. If there is always going to be a good sized load, then power factor correction is a waste of time.

If you measure the current to just a PF cap across the line, you will know the imaginary current that goes thru that cap. ( slightly off for puritans, but close onough for the real world ). Then measure the current of the motor with no load and no PF cap. Then put the PF cap across the input to the motor and measure the current. Now plot a triangle with the side proportional to the three currents you just measured.

Now rotate that triangle so the imaginary current is vertical ( the current to just the power factor cap ). Now draw a line horizontal from the angle of the triangle that is away from the imaginary current line. And extend the imaginary current line down to the horizontal line. The length of the horizontal line is the real current. And by now it ought to be obvious to the most casual observer that it isn't worth correcting the power factor completely.

Dan

That's because here, there is no such thing. I pay for the kW-hours I use and at normal domestic tariff. Period. In fact I also have a 240V off peak metered supply that I can use for water heating and other approved activities. Funnily enough my water heater is installed with a 20A plug rather than being hard wired.

Precisely what I mean about you guys being screwed over on your power systems. First you have 110V meaning you need much heavier cable to get any decent amount of current and second your suppliers screw you over on the tariffs. We have neither problem so faking 3 phase is generally a waste of effort.

PDW

Yeah but - you've got what, a single 33kV line coming to a 33kV-240V transformer now? On poles? Running the extra 2 phases isn't that big a deal.

Been there done that, cost $12K back in 1984 for the same sort of distance. The property cost $40K at the time.

Ah, the clause in the supply agreement giving the power company unfettered right to run a ROW anywhere they like to connect neighbours to the supply as a condition of giving you (or a previous owner) supply? Sorry, got little sympathy for you if so. Choice over where the ROW goes is a different matter but there are so many people with the 'stuff you Jack, I'm OK' attitude in the country these days that running power becomes even more prohibitively expensive. If you have a serious problem with allowing power ROW you can always cancel supply altogether, go solar/wind and have them remove the gear. This might not void their ability to use a ROW tho. Also the $30K for 3 phase may seem cheap when compared to solar/wind/diesel etc even for 240V 90A supply ....

So

Heh. I have a 110kV line across the front of my NSW place. They'll relocate it when hell freezes over I reckon. Then Telstra laid fibre-optic along the powerline ROW and there was nothing I could do about it either. Too bad I'd put a big dam right in the middle of the ROW under the powerlines some 10 years previously. Shrug. I knew the conditions when I bought the place.

Part of the social cost of *you* getting on the power grid is being a good citizen so others can get on the grid. I suspect from the above that you wanted the 33kV line moved back to the other side of your boundary just because someone else wanted the line extended to their place through your place. Somewhere or other, up the line, it probably crosses someone else's private land. Where would you be if they did the same thing?

Sounds familiar. However they're responsible for installed plant so you can see their reasoning. You ask for their opinion on their gear in writing then ask the area manager why it was so bad, nothing had been done? No?

Why? I had a licensed electrician check, sign & certify all work. That's all you need for anything past the electricity meter as long as you do it to code. I have a number of contractors pretty well permanently working for my group so getting stuff done isn't a problem I'd admit, but it's never been an issue on my NSW place either.

Here in Tas Aurora Energy (ex HEC) is pretty good. Their linesmen are cooperative, their staff are helpful and I have zero problems with them. I had the same experience dealing with people in NSW.

Building a

Hunt up a big VFD and use that. I got given a 4kW one. It's 3 phase in/out tho.

If you're running a farm, business etc I'd argue that it still is.

I've been thru it with the logs too. Depends if you're sawing lumber or firewood maybe. For lumber you still need to lift the log to the saw carriage & feed it thru the blade regardless of where the mill is and IMO it's easier to set up the lifting gear next to the carriage once than move it all, re-level it etc etc. A local here has a Lucas mill and for building size lumber this is a lot faster than I can haul/cut timber with my circular mill rig. In fact I buy my std size

Had my NSW place 20 years then decided to relocate to a civilised climate next to the water and play boats. Now I'm doing it all over again :-( 6 cubic metres of machine tool accessories, the small lathe and small mill just arrived. Another 10 cubic metres of machine tools still to come as that stuff is hard to replace here. I think the tractors & sawmill etc will stay on the NSW place until I decide what I'm going to do with it. 3 places is one too many.

Anyway, if you see yourself as stuck with single phase only then you are. The rotary converters don't look all that hard to do & they obviously work. As I said I'd prefer a single phase in 3 phase out VFD but I'm used to having them about the place on ships etc.

PDW

Ah haaa. Here one begins to understand why there's such a proliferation of home-brew approaches to generating three phase power in the US - a peak demand meter is invariably installed with polyphase service around here, with the idea that the user is commercial by definition if they run three phase machinery. The cost can be staggering.

Well, the utilities are pretty consistent in their treatment - we all get stuffed equally, alike - for the most part.

Jim

So, if it can be plugged in, why not plug it in? I am probably missing something here but it seems to be the obvious solution. In my shop some of the machines are plugged in. The largest plugged in machine is only 5 HP but the outlets and plugs I'm using have the capacity to be used with my 10 HP 230 volt machines. Eric

On 31 Aug 2004 19:03:48 -0700, snipped-for-privacy@krl.org (Dan Caster) vaguely proposed a theory ......and in reply I say!:

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Yes. I suppose I absorb the time, build a small one, and see what happens.

I would have to go larger for welding, though.

As I said, I saw some figures that showed that these things are not nearly as twitchy as I thought, from what I had read. They also said that welders (including GMAW etc) are fine. Electronic gear needs more care. But then I would not run a lot of electronic gear on most alternators that I could afford!

They actually seem to be far more efrficient than motor-alternators. I did not realise this as I thought it was all about money up front (which policy I applaud, but in this case could not entirely live by)

OK. Interesting.

On 31 Aug 2004 20:58:06 -0700, peter_d snipped-for-privacy@hotmail.com (Peter Wiley) vaguely proposed a theory ......and in reply I say!:

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I penned several replies to this, dealing with each statement you made. In the end I gave up.

Just this in the end. I will have to live with your judgments of me as a country citizen. You seem to have the wrong end of the stick about my situation from the comments you have mde.

On Wed, 01 Sep 2004 07:05:12 -0700, Eric R Snow vaguely proposed a theory ......and in reply I say!:

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There seems to be a misunderstanding here, to the point of discomfort. I am not deliberately being illogical. I actually regularly break this law, but some things get under the radar, others do not.

Build - If I buy one, and it can be plugged in, I can plug it in. * Buying one is an expensive option. I have seen them here (Oz) for $2000 or so for any reasonable size. I _have_ to buy motor and all, as otherwise, if I add my own motor, and any wiring, I am building it....

- If I build one and wire OR _plug_ it in, it's illegal. * Not to build (as far as I know), but to plug in. I have a 12KVA

I use tractors without ROPS, PTO shafts without covers etc etc. But as I said, some stuff slips under the radar. For some reason electricity is a very hot topic. There is a powerful trade incentive there, for a start, and it has a very high horse from which to dictate terms in order to protect itself. The building trade here is much the same. Owner building is _very_ difficult to do here.

Before you scream "nanny state" read a few of the posts about boat building in the US. We don't have anything _like_ half the rules about that here. shrug.