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Forum Index : Electronics : suppy line difference
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| brucedownunder2 Guru  Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
I wonder if some of you out there could help?? We've now got the chance to use 7 Phase , but most of us would have to rectify this up at the gennie. Would anyone have any thoughts on the overall benefit or disadvantage of which way to go by running 7 ac cables to the control box ,say 100 Metres, or leave it the way it is and run the 24v dc 100 Metres to the control box ?? Thanks Bruce Bushboy |
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi Bruce Hows the weather down there, been pouring up here for the last few days, dont think its stopped once since Monday. I run the AC down the mast, and have my recitfier at the tower base. I used 7 core trailer wire down the middle of the tower. Watch you dont buy the cheap stuff, very little copper. At the tower base I used a 7 pin trailer plug connector so I can unplug the cable when I need to untwist the drop wire, about once a week. Then I have the 7 phase bridge rectifier in a box, and finally the two wire to my shed and batteries. Having the rectifier at ground level means if there is a problem I can get to it easily. The 7 phase conversion has made all the difference to my windmill, its now runs most of the day. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Megawatt Man Senior Member  Joined: 03/05/2006 Location: AustraliaPosts: 119 |
G'day brucedownunder2, In broad terms, you'd need two wires 14 times larger than each of 7 conductors, in order to have the same voltage drop. That's because for the 7 phase balanced current arrangement the sum of the neutral conductor current is zero, so there's no neutral conductor voltage drop - and you don't even need a neutral conductor. When you add all the currents from each phase together after a set of rectifiers, there have to be two conductors of course and you are requiring each one to carry 7 times the individual phase currents. If you chose to use the same size conductors as in the 7 phase arrangement, there'd be 7 times the volytage drop in each of the two DC legs. I said broadly at the start because of inductive reactance, that isn't too much of a problem when the conductors are all close together. Also the high frequency ripple component of the 7 phase rectified output is pretty small, so won't make too much difference to the DC voltage drop. Another factor against only two wires, even if they are 14 times larger, is that the power loss in the two conductors connecting cables is double that for the 7 phase case. Megawatt Man |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
OK, Thanks Guys. I would place the rectifiers at the base of the tower (and might do so later), but my tower is on a winch and is quite easy to erect and lower,a matter of minutes. I've got 16mm square copper hard line wire (plenty) ,and at present run just 2 conductors about total 100 Mtrs for the dc and 3 conductors if I'm running 3 Phase to the conrol box . I think I've seen in the 2 wire ,dc set a total loop line resistance of .5 Ohm Now I'm thinking I maight as well use the rest of the line wire to run a total of 7 /16mm harddrawn wires to my control box -this way I'll have the rectifiers at the control box . What do you think of this idea. (just wondering if I'll be any better off). Bruce Bushboy |
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| Megawatt Man Senior Member Joined: 03/05/2006 Location: AustraliaPosts: 119 |
If your total loop resistance now is only 0.5 ohms, then the difference for running 7 wires up the tower rather than 2 won't make much difference. also the mechanical forces in your hjeavy copper conductors could lead to grief without sliprings. In my last post, I mentioned that in the case of a balanced multiphase load you don't need a neutral conductor. That's right, but if you need to provide protection for overload and possible shock, the neutral is used. Megawatt Man |
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| brucedownunder2 Guru Joined: 14/09/2005 Location: AustraliaPosts: 1548 |
Thanks Megawattman. I have spliced a multi-core flexable 2 mtr length at the top to take up any rotational action. Been blowing fairly well down here at Mt.Tamborine last couple days ,so I'm sort of getting a feel for the different configurations of the 7 Phase windings. A thing I'm finding is the lower output from these latest type magnetic rotors- Even in gale force wind I only saw 280 watts.. I,ve seen 700-800 watts out of my home made Neo rotor, but then there's the cogging restriction, but in a gale you don't get that.(we don't get many days of high wind here). If the wind continues for the next couple days ,I'll be able to compare the different configurations. Bruce Bushboy |
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