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Forum Index : Windmills : Why Low output voltage for wind turbine
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darcyrandall200 Newbie  Joined: 17/01/2009 Location: AustraliaPosts: 34 |
Hello, Why is the output voltage for wind turbines typically small? I understand that obviously a smaller output voltage is safer but I was wondering if there is any law here in Australia that requires the backyard turbine to have a low output voltage. Amoung a number of other benefits, a larger output voltage would mean less I^2 R losses and we could skimp on the cable. Thankyou. Regards Darcy Randall, Perth Western Australia |
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Madness Guru  Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
High voltage for most wind installations would mean a lot more expensive batteries. 110 Volt wind systems where around in the past. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Conventional power transformers designed for 50/60 Hz mains frequencies will work quite well at much higher frequencies, and even at lower frequencies if the operating voltage is reduced in proportion. Which tends to be the case with a wind turbine. For serious low loss ac power over reasonable distances, the cost of transformers at BOTH ends can easily offset the cost of the copper to do it at low voltage. The automatic shifting of voltage taps can also introduce some interesting possibilities. Cheers, Tony. |
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wallablack Senior Member  Joined: 10/08/2011 Location: AustraliaPosts: 164 |
IMO: Not to be taken as exact figures but a vague generalization on the DC side of things. Don't ever assume low voltage is safer.....it aint. Low voltage and high amp can be dangerous! Low Voltage - Good for charging a battery bank. Watts / Volts = Amps. Example: 1000W / 12V = 84 Amps 1000W / 24V = 42 Amps 1000W / 48V = 21 Amps Cable is rated to carry a rated amount. Fat cable carries high amps, thinner cable carries low amps. Fat cable is expensive, thinner cable is cheaper. High Amp equipment is dear, low amp equipment is generally within budget. High Voltage Turbines - Grid Connect. Say a 2Kw Wind Turbine for example. 2000W / 24VDC = 83 Amps. 2000W / 350VDC = 5.7 Amps. Grid Connect Inverters do not like high amps so therefore the high voltage (350VDC for example only) turbine produces low amps....producing the same watts. Of course a turbine requires a Turbine Controller and Dump Loads in most cases pre GC Inverter. Foolproof systems do not take into account the ingenuity of fools. |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi All High voltage is better for efficiency but several other issues make it impractical, one is the dangerous nature of high voltage DC, in the past the 32 volt system was based on the safety of unskilled operators any higher required a licence to install and maintain. Even a 32 volt system can give you a nasty shock when charging and I speak from experience on this one, had the voltage been much higher I wouldn't be here writing about it. I had a high voltage licence in Victoria many years ago and used to service up to 110 volt systems and to do this you must be super careful, make sure that the isolators are all open and keep one hand behind your back when not in use. Rubber floor mats and rubber sole boots also help but will not save fools. It is the current going across the chest from one hand to the other that stops the heart and paralyses it so it wont restart without outside help, I am not sure of current laws on HV DC but it was that when you where working on them that you always had an assistant in case of accident. Where the distance is such that it is better to transmit power in high voltage from a mill it is better to use AC and use transformer to reduce before rectification, 3 torriodal transformers and a set of rectifiers works very well but there will be some losses to consider. The other point is that there are plenty of useful devices readily available for 12 and 24 volts and to some degree for 46 volts so it is more cost effective to run a compromise system with no fried kids or grand kids. The battery issue is another cost consideration as a mini 12 volt system can be run off a 100 AH deep cycle battery to provide basics such as light (LED) and run a radio, stereo or small TV and a 12 volt pump to top up a gravity water system. Not much with our present power consumption, but in the past that would have been considered a luxury compared to candles and a kero lamp. To comply to law as I understand any work or installations of high voltage equipment must be done by a licensed person and at this time the course to get licensed is a 12 month night school, with a prerequisite of a electricians licence. My friend has just finished his course in Toowoomba and he charges $80 dollars an hour base to base so it can end up quite expensive, Can you do it yourself?, of course you can and we all do to some extent, but if something happens you are in deep sh*t not to mention loosing any insurance policy coverage on public liability or home and contents. All the best Bob PS Hi Pete Like the stubby idea but I am suspishious that you have to empty the stubbies personally before use and that is the main attraction. Foolin Around |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The only time you need a licensed person is if the equipment (whatever it is) is permanently hard connected to the power grid. If it plugs in, or has nothing to do with the mains utility, no license is required. You still have legal responsibility to take due care, just as you have driving a vehicle and many other potentially dangerous activities. But you can still change a light bulb, fix a fuse, or fit a new plug onto your electric toaster without needing an electrical license. Cheers, Tony. |
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| MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819 |
I'm not sure that that is correct in SA. I am not connected to the grid but as I understand it from speaking to local electricians ANY 240v type installation must be performed by an appropriately licensed electrician. Mind you, I used to hold a full sparkies license so did all my own wiring of the house and all anyway. My main concern is the insurance issue because I let the license lapse years ago, I'm no longer self certifying. David M. David M. |
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fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
I think we need to define the difference between ELV , LV and HV as stated in AS3000 or where I have more to do with " The Coal Mining Safety and Health Act ( 1999) ELV ( extra low voltage ) - means a voltage less than 50V ac , or 120V d.c LV ( low voltage ) - means voltage of at least 50V ac , or 120V d.c , but not more than 1,200V ac or 1500V dc HV ( high voltage ) - means voltage greater than 1,200V ac or 1,500V dc As Bob has said , even ELV has the potential to give a nasty shock, disrupt the hearts rhythm, and the human body is a good conductor and even better when wet with sweat etc. Where I work , any HV switching or isolation's are performed by 2 "compentent" persons who also must be current in Low Voltage Rescue/CPR . ELV which I would think most here would work on and note would need to be taken on the AC from the Wind being 50V ac for a 48Vdc. PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Yes Bob it can be a hazardous job, as by the 10th cell, it is possible one might put the beer in the battery and drink the acid. 
Although its one task that there is always volunteers to help out with the job.  Sometimes it just works |
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liqud Newbie Joined: 11/08/2009 Location: United StatesPosts: 22 |
Building battery banks is something I have personally abandoned strictly for maintenance and initial cost, it is not a great idea for me. I live in Chicago IL USA we may occasionally experience a power outage once a year at most for a few hours. so naturally feeding back into the grid is the sole purpose of my endeavors. High voltage in the rectified form of 180vdc feeding to an inverter that can handle 30-600vdc (that i got at a reasonable price) and outputting to the grid at a nice clean 240vac 60Hz. I do have an anti-islanding inverter as not to hurt the linemen in case of repairs to the grid. This is not the ideal situation for most low power producers I did have a 12vdc and a 24vdc set up. With no feasible need to use low voltage I kept my larger wire and produced a high voltage stator. I now have less loss with #2awg wire and higher voltage. wattage divided by voltage equals amperage Finding the correct controls and protection was not as hard as i had thought most industrial hardware you can find is rated for HVDC as well as HVAC (not all, read the datasheets first!). Other components i.e. dumpload had to be handmade and works excellently so. I am a commercial and industrial electrician in Chicago and have a lot of experience with HV AC/DC. Proper shielding and grounding is the biggest concern when working with HV. Using hard pipe EMT RGD is a great Primary Ground but always use an appropriately sized and marked secondary ground wire. Keep DC and AC grounded separately and always a good idea to have a lightning arrestor on your pole. In response to VK4AYQ If at all possibly do not work on HOT circuits. if you are working on a wind turbine turn on your brake pull your utility disconnect and work in a safer environment. The mortality rate in the electrical field is high mostly due to carelessness. wooden or fiberglass ladders proper gear as VK4AYQ has said. put these safety measure in place and you will be glad you did. most places wont let you grid tie in until you do anyway. I have included a short read on arc calculations. http://www.arcadvisor.com/faq/dc_direct_current_arc.html] hope this helps im a little late on the posting here anyway. Shawn C Real power is not given its made... |
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