Re (2): UPS with earth leakage device.
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From: GangGreene on 9 Jan 2010 08:24 ArameFarpado wrote: > Em Sábado 09 Janeiro 2010 11:52, Henrik Carlqvist escreveu: > >> ArameFarpado <a-farpado.spam(a)netcabo.pt> wrote: >> >>> Em Sábado 09 Janeiro 2010 05:28, jellybean stonerfish escreveu: >> >>>> On Sat, 09 Jan 2010 00:05:57 +0000, ArameFarpado wrote: >> >>>>> Em Sexta 08 Janeiro 2010 18:28, jellybean stonerfish escreveu: >> >>>>>> On Fri, 08 Jan 2010 13:17:38 +0000, ArameFarpado wrote: >>>>>>> anothter question if you don't mind: >>>>>>> a lightning bolt falls in the ground at 6 meters from you and a cow, >>>>>>> you suffer nothing while the cow gets electricuted and dies... why? >> >>>>>> Tennis shoes? >> >>>>> bare feet just like the cow >>>> >>>> 2 legs?? >>> the man has 2 legs and they are standing more or less at the same point, >>> the cow has 2 legs about 1 meter apart from the other 2... ring any >>> bells? >> >> <OT> >> >> If both the cow and the man were standing on their legs instead of lying >> flat on the ground or even better in some pit below the ground surface >> the lightning would not hit 6 meters from them. Instead the lightning >> would hit the highest point connected to the ground which would probably >> be the mans head. So my guess is that the cow has the best chance of >> surviving after all. >> >> </OT> >> >> regards Henrik > > you are driving away from the problem: > the bolt didn't hit the human or the cow, it hit the ground or a tree at 6 > meters from them, the man only gets scared while the cow dies > electricuted... why? > > this is all related to the fact the earth's electrical potential is not > the same in every place. It depends upon the reference point.
From: jellybean stonerfish on 9 Jan 2010 12:25 On Sat, 09 Jan 2010 11:19:39 +0000, ArameFarpado wrote: > Em Sábado 09 Janeiro 2010 05:28, jellybean stonerfish escreveu: >> 2 legs?? > the man has 2 legs and they are standing more or less at the same point, > the cow has 2 legs about 1 meter apart from the other 2... ring any > bells? > OK, I understand your hypothetical. > >> On the side, just to keep this post entertaining... >> >> Q: Why did the cow say "Mooooove" ? > don't know, no cow ever spoke to me... :) A: Because she didn't have a horn.
From: ArameFarpado on 9 Jan 2010 13:40 Em Sábado 09 Janeiro 2010 13:22, GangGreene escreveu: > ArameFarpado wrote: > > [putolin] > >>> >>> Guys/Gals Please >>> >>> One question.... >>> >>> How many wires from an electical substation to the trasformer on the >>> pole? >> >> 3 life phases, each AC with it's sinosoidal wave lagged 120º to the >> others. every time 2 phases are positive there is one negative and >> vice-versa. >> >> no need for neutral here. >> >>> >>> Answer One. >>> >>> There is no neutral. >>> The power is returned through the earth, through a ground system. >> no. the electric circuit is closed between those 3 phases >> >> there is a triphasic wave form here >> http://www.animations.physics.unsw.edu.au/jw/images/power_files/3phase.gif >> >> notice when 2 phases are positive there 1 negative and so on. >> there is allways tension between them. >> >> http://www.windstuffnow.com/main/3_phase_basics.htm > > You are mixed up. oh really > I am talking residential power distribution you are > talking appliance distribution. quoting you: >>> How many wires from an electical substation to the trasformer on the >>> pole? substation to transformer is residential distribution? since when? > Notice only one leg of the 3 phase is coming down from the overhead 3 > phase lines over head to the xmfr on the pole. what poles are you talking about? high tension or low tension? > If it was as you believe then two legs of the 3 phase would be in use. > It's not. what poles are you talking about... ? http://images02.olx.com.br/ui/2/52/03/34504903_2.jpg these ones? > So tell me why is one leg used on the xfmr and one bare copper line going > from the xfmr down the pole to a ground rod beside the power pole for > then? aren't you imagining things? > Also when talking polyphase power distribution why then is a grounded > conductor used/required on the service entrance drop from the pole to the > residence? tri-phasic residential distribution is done with 4 wires: 3 phases and 1 neutral, the neutral is necessary for monophasic devices. in europe we have 400volts between phases and 230volts between any phase and neutral, if you have 400volts light bolbs then you can connect them between 2 phases, but all monophasic devices are 230volts over here, so the distribution company must provide the neutral along with the phases. it is also common to see 3 phases and a neutral entering a bilding only for monophasic service, that's about balance the phases: 1 phase feeds 1/3 of the apartments, the 2nd fase the other 1/3 and the 3rd phase feeds the last 1/3 of the apartments. the electrical company don't provide the earth wire, every bilding has it's own and it is not requered for things to work, it's only a safety protection that you should connect to the body of any metallic electric device. notice that the neutral isn't just a ground connection; it is a central point of the secundary of a triphasic transformer whose coils are connected in "star" mode like this http://www.cefetsp.br/edu/jaan/mestrado/Image63.gif A,B and C are the phases, and N will be the neutral, it is not represented but the N line to became a real neutral needs to be grounded also. > > If it worked as you say it would only require two conductors to be brought > to the residence. > > http://science.howstuffworks.com/power.html > > http://www.howstuffworks.com/framed.htm?parent=power.htm&url=http://www.epanorama.net/documents/groundloop/mains_connectors.html here you go, your link has a squematic showind the star center connected to the groung but still moving on to it's destiny as a neutral wire.
From: Moe Trin on 9 Jan 2010 16:40 On Sat, 09 Jan 2010, in the Usenet newsgroup comp.os.linux.hardware, in article <4b47c84e$0$272$14726298(a)news.sunsite.dk>, ArameFarpado wrote: >Joe Pfeiffer escreveu: >> I guess I wasn't explicit enough: it's bonded to ground at *your* >> *house's* service panel -- i.e. the "breaker box". The whole point >> is to avoid having neutral at a different potential than ground. >No it isn't, not in europe anyway... That's another point - the _world_ doesn't follow European standards any more than North American, Chinese, Brazilian or Algerian standards. >neutral comes from the outside allready a neutral, it's discharge is >done right in the secundary side of the transformer that feeds the >bilding or block of bildings. and that is done with several copper >rods sticked in the ground "discharge" of what? Neutral is only relevant when there are more than one phase - another word used is "common". >then every bilding has it's own copper rod, and it's earth does not >connect with neutral... it's commom to have about 2volts between >earth and neutral over here. That's a European custom - it's not how it's done elsewhere, including most specifically in North America. The ground and return lead (what you keep referring to as the 'neutral') MUST BE joined in the distribution panel. It's a legal requirement here. >>> a lightning bolt falls in the ground at 6 meters from you and a >>> cow, you suffer nothing while the cow gets electricuted and >>> dies... why? >you don't know why? No one is interested in games. I assume you are thinking that the legs of the cow are straddling a potential difference, but that is equally likely for the person. >most home ups aren't really ups at all, some of them can't even feed >the pc after the main power is gone, they are isolation transformers. Then you should not be buying something from such a fraudulent supplier. Isolation transformers are not sold as an UPS - which means Uninterruptable Power Supply. Consult your lawyer. Old guy
From: Moe Trin on 9 Jan 2010 16:42
On Sat, 09 Jan 2010, in the Usenet newsgroup comp.os.linux.hardware, in article <4b47d15a$0$270$14726298(a)news.sunsite.dk>, ArameFarpado wrote: >Moe Trin escreveu: >> So by your definition, there can not be a "neutral" in a car or >> airplane. >no neutral, cars and planes have a body and one if it's poles is >connected to the body, usualy the negative pole. The metallic body (more correctly the frame) is being used as a conductor. Most cars do not have multiple electrical systems. Planes with more than one engine ALWAYS do - and even single engine aircraft often have more than one electrical system. Something like an airliner will have a minimum of three electrical systems (a legal requirement), often more. Each has it's own generator or alternator (28 VDC or 115/200 V3Phase400Hz). Some _may_ also have a very limited amount of 50/60 Hz single phase in the lavatories for passenger use. >planes have a kind of stick that touches he ground (and some cars >also) to put the body at the same potential as the ground they are >standing; I am a commercial airplane pilot, and have had my license for over 30 years. You are absolutely wrong in this statement. There is no "stick" and never has been - simple mechanical problems like the compression of the tires, and wind resistance preclude it, never mind the considerable maintenance issue of constantly replacing it when it would be knocked off by the ground contact. >planes must have this or people could get electricuted by touching >the plane body after a landing... What is the resistance of the rubber compound used in tires? Assume an aircraft with a surface area of 350 square meters sitting 2.0 meters off the ground (equivalent to a capacity of ~1600 picofarad) and a tire resistance of 250 MegOhms. Do you know how to compute (electrical) discharge time constants? How many seconds will it take to dissipate a static charge (math: 1 TC ~ 0.25 seconds)? The only time airplanes are intentionally connected to an electrical ground is during refueling operations - the plane gets grounded, as does the fuel truck or hydrant, and a separate ground connection is made between the fuel hose and the aircraft before the host/nozzle is allowed to touch the aircraft. This is to prevent static discharges from causing a spark and igniting the fuel vapo[u]rs. >some people more sensitive to estatic also place this sticks in >there cars so they don't get shocked when they touch them or when >the put the feet on the ground getting out of the car. Quite a lively imagination you have - same problem as with the "stick" you claim is on aircraft: compression of the tires as well as the movement of the suspension system, and the maintenance issues. It used to be common for fuel trucks to have a length of steel chain dragging on the ground to discharge any static build-up. The end of the chain would eventually wear enough to allow the chain to break, often leaving sharp pieces of metal on the highways. This discharge function has been transferred to the tires, which are slightly conductive due to the carbon black material used in creating the tire. When the fuel trucks are loaded or unloaded, they have the same grounding wire technique used with aircraft. Next time you see petrol/gasoline being delivered by truck at a gas/petrol/fuel station notice the grounding wires connecting the truck and hoses to the ground lugs. Old guy |