Posted by jackinok on September 12, 2012 at 12:05:45 from (162.58.82.136):
In Reply to: Re: OT Windmills OT posted by ldj on September 12, 2012 at 11:20:28:
your confusing transmission lines with distribution lines. transmission lines generaly come out of a power plant run for miles and miles sometimes coast to coast,which is why a power plant failure in arizona causes a blackout or brownout in new york city.common voltages would be something on the order of 169000+.the voltage have to be that high to make up for power losses due to the miles they run.these are normaly all overhead simply for ease of repair and fault finding. once they reach a distribution point they run into substations which lower the voltages normally in the 7200-20,000 range. lines out of the substation are very often underground,simply because if theres a failure its localized.these lines are called distribution lines.and the distributing system starts with them.these are the lines that you see beside the road running to the transformer on you pole,or to the pad mounted transformer on the ground.the transformer simply lowers voltage even further to the ones used in your shop or home. on a wind generating system since it is a multiple source system these lines can run under ground( though they often are in large conduits) even though voltages are high, simply because if you lose one it just shuts down and load switches to another local source. if these same lines running from a single source such as a generating plant goes down the tremendous loads on them often cause a cascade failure that takes out switching systems , other plants ,etc etc. and has at least the potential of taking down electrical systems in a large portion of a state or the country. normally,if their is such a thing, a wind farm would be wired into the distribution side of this so they could run a localized area,therefor relieving the load off the transmission system.but they can be miles and miles from the end energy user,and tie into that grid. another reason line are not overhead in a wind farm generally is they would be in the way of the mill tracking the wind.law requires these lines be a min of so many feet off the ground( used to be 25 feet at their lowest point) by having them overhead blade tip hieght would have to be more adding greatly to the cost of the towers etc.
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