Archive for November 30th, 2010

Electric Train Sets For Sale

November 30th, 2010 dwalton
... Rails Electric Train Set

Electric arc

Author: tianli

Overview

Electricity arcs between the power rail and electrical pickup "shoe" on a London Underground train

Electric arc between hairs of multistranded wire.

The various shapes of electric arc are emergent properties of nonlinear patterns of current and electric field. The arc occurs in the gas-filled space between two conductive electrodes (often made of carbon) and it results in a very high temperature, capable of melting or vaporizing most materials. An electric arc is a continuous discharge, while a similar electric spark discharge is momentary. An electric arc may occur either in Direct current circuits or in alternating current circuits. In the latter case, the arc may re-strike on each half cycle of the current. An electric arc differs from a glow discharge in that the current density is quite high, and the voltage drop within the arc is low; at the cathode the current density may be as high as one megaampere per square centimeter.

An electric arc has a non-linear relationship between current and voltage. Once the arc is established (either by progression from a glow discharge or by momentarily touching the electrodes then separating them), increased current results in a lower voltage between the arc terminals. This negative resistance effect requires that some positive form of impedance to be placed in the circuit, if it is desired to maintain a stable arc. This property is the reason uncontrolled electrical arcs in apparatus become so destructive, since once initiated an arc will draw more and more current from a fixed-voltage supply until the apparatus is destroyed.

Uses

An electric arc can melt calcium oxide

Industrially, electric arcs are used for welding, plasma cutting, for electrical discharge machining, as an arc lamp in movie projectors and followspots in stage lighting. Electric arc furnaces are used to produce steel and other substances. Calcium carbide is made in this way as it requires a large amount of energy to promote an endothermic reaction (at temperatures of 2500 C).

Low-pressure electric arcs are used for lighting, e.g., fluorescent tubes, mercury and sodium street lamps, and camera flash lamps.

Formation of an intense electric arc, similar to a small-scale arc flash, is the foundation of exploding-bridgewire detonators.

Electric arcs have been studied for electric propulsion of spacecraft.

Undesired arcing

Arc damage to a CEE 7/7 plug. The discharge path was formed by a conductive liquid seeping into the plug-socket assembly.

Undesired or unintended electric arcing can have detrimental effects on electric power transmission, distribution systems and electronic equipment. Devices which may cause arcing include switches, circuit breakers, relay contacts, fuses and poor cable terminations. When an inductive circuit is switched off the current cannot instantaneously jump to zero; a transient arc will be formed across the separating contacts. Switching devices susceptible to arcing are normally designed to contain and extinguish an arc, and snubber circuits can supply a path for transient currents, preventing arcing. If a circuit has enough current and voltage to sustain an arc formed outside of a switching device, the arc can cause damage to equipment such as melting of conductors, destruction of insulation, and fire. An arc flash describes an explosive electrical event that presents a hazard to people and equipment.

Undesired arcing in electrical contactors can be suppressed by various devices, including:

immersion in oil, inert gas or vacuum

arc chutes

magnetic blowouts

Arcing can also occur when a low resistance channel (foreign object, conductive dust, moisture...) forms between places with different potential. The conductive channel then can facilitate formation of an electric arc. The ionized air has high electrical conductivity approaching that of metals, and can conduct extremely high currents, causing a short circuit and tripping protective devices (fuses, circuit breakers). Similar situation may occur when a lightbulb burns out and the fragments of the filament pull an electric arc between the leads inside the bulb, leading to overcurrent that trips the breakers.

Electric arc over the surface of plastics causes their degradation. A conductive carbon-rich track tends to form in the arc path, negatively influencing their insulation properties. The arc susceptibility is tested according to ASTM D495, by point electrodes and continuous and intermittent arcs; it is measured in seconds to form a track that is conductive under high-voltage low-current conditions. Some materials are less susceptible to degradation than others; e.g. polytetrafluoroethylene has arc resistance of about 200 seconds. From thermosetting plastics, alkyds and melamine resins are better than phenolic resins. Polyethylenes have arc resistance of about 150 seconds, polystyrenes and polyvinyl chlorides have relatively low resistance of about 70 seconds. Plastics can be formulated to emit gases with arc-extinguishing properties; these are known as arc-extinguishing plastics.

Arcing over some types of printed circuit boards, possibly due to cracks of the traces or the failure of a solder, renders the affected insulating layer conductive as the dielectric is combusted due to the high temperatures involved. This conductivity prolongs the arcing due to cascading failure of the surface.

See also

Arc transmitter

Marx generator

Spark gap

Vacuum arc

References

^ A. H. Howatson, An Introduction to Gas Discharges, Pergamon Press, Oxford pgs. 80-95

^ Principles of Electronics By V.K. Mehta ISBN 8121924502 pages 101-107

External links

Wikimedia Commons has media related to: Electric arc

Unusual Arcing Photos

Some more info about making electric arcs using a welder.

Videos of 230 kV 3-phase "Jacobs Ladder" and unintentional 500 kV power arc

High Voltage Arc Gap Calculator to calculate the length of an arc knowing the voltage or vice versa

Electric Arc Calculator

Categories: Electric arcs

Article Source: http://www.articlesbase.com/sales-articles/electric-arc-2803840.html

About the Author

I am an expert from China Suppliers, usually analyzes all kind of industries situation, such as vintage yamaha parts , pit bike graphics.



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Electric Train Sets For Children

November 30th, 2010 dwalton
Cast G-Scale Electric Train ...

How to Cut Your Electric Bill In Half

Author: Kyle

America uses up a lot of todays energy. But not for free! That electric bill nagging you month after month is a result inefficient use of energy. It is time to act and cut down your electric bill by 50% or more. Heres how you can do it:

 

Use full loads when cleaning dishes or clothes. What do you think consumes more energy, running the washing machine twice with two half loads, or once with a full load? You should always wait until you can completely fill up your dishwasher or washing machine. This will not only save energy, but also heat, water, and soap.

 

Don't just turn off, unplug. Never leave any devices (like computer monitors) on. But don't stop at just turning it off, unplug it! A lot of things do not actually turn “off” when they are powered down, they actually enter into a standby phase. Likewise, they eat up a ton of energy throughout the year just sitting there. The best way to unplug is to buy power strips. After attaching all your electric accessories to the power strip, all you have to do is unplug this power strip which will cut off the flow of electricity.

 

Use common energy sense. Everything you do will require energy, but be “energy smart”. Here are some simple ideas to help cut down your electricity use: Instead of using warm water to wash clothes, use cold. This will eliminate the energy used to heat up the water. Always air dry your dishes. Just open the dishwasher door and let it sit for an hour. Use oven heat for your house, when you need your house warmer, leave the oven door open after cooking something. Don't let that heat go to waste. Take short showers, not baths. This uses up a much smaller amount of water and energy. Use fluorescent light bulbs. These might same more expensive, but in the long run, you will save a lot of energy with those. Also, don't forget to turn out the lights when you leave a room! These are just a few ideas to reserve energy, there are a lot more!

Article Source: http://www.articlesbase.com/tools-and-equipment-articles/how-to-cut-your-electric-bill-in-half-1219153.html

About the Author

Don't miss out, completely eliminate your electric bill with solar and wind energy! Most solar panels cost over twenty-thousand dollars to buy and install! That is not affordable, and is a big waste of cash! Now, get your whole house solar and wind powered by making solar panels for as low as thirty dollars! Its incredible! Check out this finally revealed secret at: http://7192ah2n2zxggr99lf0a7u2nf0.hop.clickbank.net/


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Electric Train Sets For Kids

November 30th, 2010 dwalton
... set on Flickr

Electric Generators Give Home on the Range a New Meaning!

Author: Abigail Franks

Power generators are one of the most valuable pieces of equipment when they're needed. During power outages or in locations where plugging into the electric grid is not an option, a portable power generator can come in real handy. Unfortunately it also can be a very bad neighbor due to the noise factor. Imagine traveling out to the wilderness only to listen to the generator roar from the neighbors camp set up. Not good. So if you're considering getting a generator, be very aware of the operational noise and select a high quality, quiet electrical generator.

If you are considering buying a generator, make sure that you take the time to consider a Honda power generator. The Honda power generator has superior insualative properties over most other brands so it runs very quietly. Many people may not think that spending extra money on a generator just because it is quiet is prudent, but a quiet generator is very important in many cases. Tailgating and camping are two of those cases.

Tailgate parties are usually thrown during sports seasons where people get together at the stadium to have a cook out prior to enjoying the game. Although 110 volt electrical power is a great convenience, it's also very noisy if you select the wrong power generator source.

A couple years ago, we went to a local football game even though we had no tickets just went to enjoy the pre-game festivities and food. We decided that if we did not find anyone selling tickets in the parking lot, then we would just watch the game on the television located in the camper on our truck. Short story is that we didn't get tickets and were able to use our quiet generator to view the game in the comfort of our own recreational vehicle.

We soon discovered the benefits of having a quiet generator like the Honda power generator because we had the benefit of a quiet generator. The television required electricity. There was no way that we were missing the game so we just powered up the generator and had all the comforts of home right in the back of our truck.

We had no noise complaints due to the quiet operating generator. The people in an adjoining motor home however weren't so lucky. They're gen-set was an older unit that was noisy and clanked away while still generating the electricity. These poor folks had others coming over and complaining all the time because of the noise. It just wasn't worth the problems or ugly behavior so they had to turn off their power source.

The moral of the story is that it's not good to pay to little for a generator but it's also not good to pay to little. Get the best value once again pays dividends for the life of the purchase. Consider a quality, quiet electrical power generator for your next outing.

Article Source: http://www.articlesbase.com/home-improvement-articles/electric-generators-give-home-on-the-range-a-new-meaning-38196.html

About the Author

Abigail Franks writes on many subjects dealing with home, pets, and family. To find more nformation on Electric Generators visit http://www.generators.outsidemagic.com



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