Saturday, 5 March 2011

Kill an elephant to prove a point – best system AC or DC

Arguably Thomas Edison's best success was his ability to maximize his profits by establishing mass production systems as well as intellectual property rights.  By 1887, there were 121 of Edison's power stations that were delivering electricity to customers in the United States

He continued to promote DC electricity rather than AC electricity.  This continued to be a competition between Edison and Westinghouse, who preferred AC electricity which could be raised to high voltages with the use of transformers and sent over cheaper wires. 

In order to demonstrate his view of AC electricity and his dangers, employees of Edison would publicly electrocute animals.  One of these animals was Topsy the elephant at Luna Park following Topsy's killing of several men. 

Thomas Edison filed for a patent for his carbon filament lamp.  In 1878, Edison formed the Edison Electric lIght Company with the assistance of several financiers.  He had a demonstration of the incandescent light bulb for the public on December 31, 1879.  In 1883, it was ruled by the patent office that Edison's patent was based on the work of William Sawyer.  Therefore, the patent was considered invalid.  The litigation on the case continued for six years.  Edison and Joseph Swan formed a joint company in order to manufacture the invention. 

On the other hand in Europe we have a different, some say better system
Electric motors, power generation, electricity delivered over great distances, radio and even those sparking towers in the Frankenstein films - a Yugoslav-born electrical engineer is the one to thank
Many children are familiar with the Tesla coil - used at science demonstrations and lectures to demonstrate what happens when you discharge a high voltage (but low current: it's current that kills, not voltage) over a small space. Films of Frankenstein often show, somewhat anachronistically, Tesla coils discharging lightning-like bolts like billy-o.
Tesla, an ethnic Serb from Smiljan, then part of the Austro-Hungarian empire, started out his engineering life working for a telephone company in Budapest in 1881, aged 24. He'd already studied physics and maths; While there - while walking in a park, in fact - he had an inspiration and solved the equations relating to a revolving magnetic field. Which he then drew in the ground with a stick and explained to a friend. Quite a patient friend, one suspects.
Not much to you, perhaps, but those equations govern the induction motor, which is now the most common form of electric motor: put three coils around an outside former, and put a rotating element inside. If you run a current through the outside coils, and get the timing just right, then you create a current (and hence magnetic force) in the coils in the inside. So the inside rotor turns, but it doesn't have to touch the outer part: less friction means less energy used. (Compare that method to the carbon brushes needed in standard DC motors, which wear away where they touch the inner rotor.)
But it's in the development of mains electricity - the underpinning of our modern age - that Tesla really rules. When Americans tell the story of Thomas Edison, the famous inventor of the gramophone, and whose name is usually attached to the invention of the light bulb, Tesla's name is frequently left out.
However Tesla, who became an American citizen in 1891, worked with Edison for years, improving many of the early inventions and turning them into something workable. (The two were introduced in 1884, when Tesla came to the US, by a letter from a mutual friend to Edison which read "I know of two great men. One is you and the other is this young man.")

Yet it's thanks to Tesla, not Edison, that we have electricity coming out of plugs, and that we even have power stations able to generate serious amounts of energy. He won "the war of the currents" with Edison, who was convinced that direct current (DC) - the sort that comes out of an ordinary battery - was the way forward for power generation and distribution. Tesla was able to show that alternating current (AC) - which swaps its polarity at a regular rate, 50 times a second in UK mains electricity - was far more efficient (you don't lose anything like as much energy in transmitting it over long distances).

Even though Edison took to electrocuting dogs in public displays to show just how dangerous AC was (no, really), Tesla won the day. Where DC could only be transmitted for a couple of miles before the resistance of the lines reduced it to nothing, AC can be transmitted at high voltages for many times that distance. (A side note: did you know that the distribution equipment - transformers, transmission lines - is 80% of the cost of running an electricity company? The power generation is only 20%. Which is why even if we had free electricity generation - say from nuclear fusion - the upkeep of the distribution network would still mean you'd get a bill every quarter. Quite probably it would still be for the house next door which isn't on the same provider, too.)

having said all this, Irony upon irony .... Just as his most famous stolen legacy, the incandescent light bulb, heads for extinction, his other great passion, direct electric current, is set to boom. The bulb that has dominated lighting for more than a century is now a pariah in the era of climate change and banned in many countries. Meanwhile, direct current - defeated by alternating current in the race to capture the electricity market in the 1890s - could help us hold back global warming.


No comments:

Post a Comment