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Thread: Clarifying 3ph Motor connections
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1st Feb 2014, 07:17 PM #91
I am starting to get a slight inkling of the picture. I think I know what is being said, maybe.
OK I get it.
Thanks. At least I have not let earth shattering news pass by without noticing. Now I can breath easy. Nobody likes to look like a fool.
On another related note, I took the fire truck out for a test run today and while I was testing the water pump, I noticed that there were "3", yes "3" power wires above, just as I hit one of them with the jet of water. Oops. This means, to those who don't remember every post I have written (everyone including me) that 3ph power is only 4.5km from my place. That shouldn't be too expensive to arrange should it?
Dean
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1st Feb 2014, 08:20 PM #92Most Valued Member
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1st Feb 2014, 09:01 PM #93
No sweat Stuart. If the price was right today they would be a good option for drill presses and other small machines that are suited to a vfd. I was just checking that I had not made a mistake.
They will not handle 7.5hp and that is that.
I would like to fit a vfd to a drill press. Just not the one I have now. It is not good enough and it is single phase. If I manage to find a good drill press (Waldown) I will fit one. The price will decide what type.
Dean
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1st Feb 2014, 09:08 PM #94
Hi Dean
I am pretty sure there should be 4 wires for 3 phase power lines-3 phases and neutral. I have four coming into my meter box. All the machines i have only use the 3 phases, no neutral. the voltage difference between each phase is 415v, from any phase to neutral is 240v.
Not sure why you would have 3 wires?
Ew1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.
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1st Feb 2014, 09:14 PM #95Most Valued Member
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Hi Dean,
I seem to have confused you. They are available "up to at least 7 1/2 Hp".
They infact make them up to at least 20hp
Drives Direct - Digital Phase Converters - Digital Inverters 240 - 415 (scroll down for prices)
items in Drives Direct Inverters LTD store on eBay!
7½ HP 220V to 415V 3 PHASE DIGITAL INVERTER CONVERTER | eBay?
Still doesnt make them cheap
Stuart
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1st Feb 2014, 09:19 PM #96
Must be a Canberra thing!
I have to say that I don't really know. I do know that all the power lines I am used to seeing along the road (in S.A.) have 3 wires. The ones I mostly see in Vic have 1 wire. The one wire is SWER. Single wire earth return. The neutral is under your feet. You're standing on it. That's the my limit of knowledge.
Dean
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1st Feb 2014, 09:24 PM #97
Ok, so our power lines are 240V local grids with transformers for each grid/section. SWER runs at a much higher voltage and has a tranny at each break out point. Makes sense for long runs where the cost of the 2nd wire is more than the cost of the tranny.
Our ground my not be conductive enough either-don't know.
Ew1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.
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1st Feb 2014, 09:33 PM #98
No Stuart. That would have been a result of reading this quote from a previous post.
Where a normal VFD uses a full-wave bridge rectifier to convert 240VAC ac into 340VDC (240*1.41=338.5), these VFD's use a half-wave voltage doubler circuit to convert 120VAC into 340VDC. As far as I know, these VFD's are only manufactured for very low horsepower motors. They are paticularly popular in the USA, where many houses are only fed with 110 or 120V. These household powerpoints are limited to 15A. 15A*120V=1800W or 2.4HP, less the losses in a VFD makes for about max 2HP drive power. Due to the larger capacitors needed, such VFD's will be a little larger and more costly than plain 240V input VFD's. ChrisChrisdid say "As far as I know".
Prices are not massively more expensive. Only about 4 times what I have paid, although I have not got a 7.5hp unit. I am still happy with what I have got for now. I will remember about them though, as I may be richer at some stage in the future.
Thanks for the help Stuart andChris.
Dean
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1st Feb 2014, 09:51 PM #99
The 3 wires run parallel to the border with SWER lines from there, down roads that lead towards the border and maybe the other way as well. I haven't actually looked. About 11.5 km for our road. Correct regards the trannies/wires. No-one important lives down there anyway!
I am not sure about your ground, but have you any idea how conductive dry sand is? That is what we have during the summer. I could use the soil from some places for cement! At my last place I did. In winter it is water logged sand and in between it is well, in between.
I believe that SWER has safety issues that make it better not to use it in residential areas. I guess that means that we are not important enough to get safe wiring. Goes back to bang for buck. I think the safety issue is for people working on the power lines so they have to take the correct precautions. They will not work on live power lines, but I think that may be more common all over now anyway. The one major problem with SWER is that it is not able to carry 3ph.
Dean
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2nd Feb 2014, 01:01 AM #100
Hi Guys,
Excuse this pommy sticking his neb in !
I think you will find that those three wires are probably 11Kv or there abouts and at the end of those three wires is a transformer reducing the voltage to 440/415 three phase. Its at this point you can choose a neutral connection at the star point and get the 240v from phase to neutral. This now becomes four wires. I don't know about OZ but in the UK the neutral gets earthed either at the distribution transformer or at the home/dwelling to create a safety earth connection.Best Regards:
Baron J.
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2nd Feb 2014, 08:12 AM #101
As I have said, I am not an expert, but I do think you are right Baron. I would guess there are some differences with country/city arrangements due to cost and suitability.
11Kv? Again, probably right as I thought the wires looked pretty small while I was hitting one of them with the jet from the fire pump. I think in the case of the SWER line that a single phase of the 11Kv line would be used for each of these. I doubt that 415v would survive 14.5km. There is also a fuse that connects the line to my transformer which is about 600mm long. I have seen a linesman replacing this at about Midnight after a sugar glider got crisped. A tricky job. All done from the ground with a long and extremely flexible, extendable (about 8 sections) fiberglass (guess) pole. My point is that a fuse of this size would not be needed for 415v. It is supposed to fall off when blown, but in this case it stayed in place making the job harder.
Dean
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2nd Feb 2014, 09:07 AM #102Cba
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Some info on digital phase converters from an Assie maker:
Phase Converter Info
and some good info from Drives Direct on digital phase converters:
Drives Direct - Digital Phase Converters - How To Choose
A digital phase converter is not always also a VFD. A digital phase converter normally produces a fixed 50Hz three phase output (without the pwm modulation and frequency contol etc that a VFD has). That you can use to attach one or several fixed speed motors, and/or one or several VFD drives.
There are also voltage step-up digital phase converters. I would recommend to check if the same result cannot be obtained cheaper by using a simple and long lasting step-up transformer before (single phase) or after (3-phase) a digital converter.
Digital phase converters that can do in one box the 3-pase conversion AND voltage step-up AND also have a VFD output are something new I was not aware of. Hopefully prices for these will come down once the novelty effect goes and more makers offer this combination. Chris
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3rd Feb 2014, 01:41 AM #103
Hi Dean,
Its unlikely that a SWER would be used at 11Kv over any distance. SWER would be where the transformer at the end of the line dropped the 11Kv down to 440/415 for distribution to a local area. Even then in the UK it would only be at the 240V level for local distribution.
Re the fuse: That sounds about right. The 11Kv pole fuse should fall away when it blows. The idea being that it creates a large gap between the load and supply. Sometimes the top of the fuse gets spark welded to the horn when the fuse is replaced if there is a load still on the line when its done.Best Regards:
Baron J.
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3rd Feb 2014, 08:33 PM #104
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3rd Feb 2014, 10:27 PM #105
Clearly different countries have different standards or policies. Our power supply is via SWER line and comes form 12km away from a 50kV transformer....
Cheers, Joe
retired - less energy, more time to contemplate projects and more shed time....