Wednesday, March 22, 2006

Nicola Tesla had it right

It's interesting how we came to have our current mess of global voltage standards - a problem which every traveler deals with on a recurring basis. Nicola Tesla did some great empirical work in the 1860s to determine that 220vac at 60Hz was the optimal combination (at least for motors, which were the key to having an electricity business in the late 19th century) but Edison forced 110vac on the US because that's what his DC generators on Pearl Street in NYC ran at. And post WWII the Europeans decided to follow suit when they rebuilt, but wanted 50Hz because that fit with the 1,2,5 numbers in the metric system. But at 50Hz motor efficiency drops about 15-20%, which is especially a problem as you move further from the transformer and voltage drops, so they decided to go with 240vac to make up the difference. Who says it's science? Here's the full story.

The system of three-phase alternating current electrical generation and distribution was invented by a nineteenth centuryby the ideosyncratic electrical genius Nicola Tesla. Tesla was considered the reigning authority on alternating current in that day (Edison was promoting direct current systems, thinking AC too dangerous for commercial use). When air brake tycoon George Westinghouse invested in AC distribution systems, which could bridge the distance between his generators in Niagra Falls and his markets in New York City because of their low line losses, he consulted Nicola Tesla on developing a motor (a key part of the whole system, just as the light bulb was the key component in Edison's systems).

Tesla made many careful calculations and measurements and found out that 60 Hz (Hertz, cycles per second) was the best frequency for alternating current (AC) power generating. He preferred 240 volts, which put him at odds with Thomas Edison, whose direct current (DC) systems were 110 volts. Perhaps Edison had a useful point in the safety factor of the lower voltage, but DC couldn't provide the power to a distance that AC could.

Tesla built Westinghouse a prototype motor, optimized for 60 Hz and 240 volts AC. Westinghouse's original system ran at 133 Hz, and not surprisingly, Tesla's motors failed to put out any power at that frequency. Westinghouse's own engineers tried to redesign the motor (Tesla would have nothing to do with redesign, insisting that Westinghouse change his generating network to 60 Hz and 240 volts). The rest is history, as Westinghouse gave in to Tesla (and more importantly, the laws of physics) and changed is grid to 60 Hz - our standard today. Thomas Edison, the largest player in the electrification business in the US, initially conducted smear campaigns against Westinghouse's system (he even coined the term 'Westinghousing' for execution of criminals in the electric chair) arguing that alternating current was too dangerous for domestic use, sometimes accompanied by garish public electrocutions of stray dogs just to demonstrate. But Edison ultimately came to believe in the superiority of AC, and switched his 110 volt DC systems over 110 volt AC systems, which is where we get our US standard of 60 Hz and 110 volts AC.

When electricity was first introduced into households it was primarily for lighting, largely due to Edison's marketing of lighting as being the 'killer app' that would justify a households investment in electrification (motors were more important for industrial factories). All original electrical appliances had a screw-in light socket connector. However, as it became a viable alternative to other means of heating and also the development of labour saving appliances, a means of connection to the supply other than via a light socket was required. In the 1920s, the two-prong plug made its appearance. At that time, some electricity companies operated a split tariff system where the cost of electricity for lighting was lower than that for other purposes, which led to low wattage appliances (e.g. vacuum cleaners, hair dryers, etc.) being connected to the light fitting. Europe followed suit with adoption of 120 volt systems.

As the need for safer installations grew, three-pin outlets were developed. The third pin on the outlet was an grounding pin, which was effectively connected to ground, this being at the same potential as the neutral supply line. The idea behind it was that in the event of a short circuit to ground, a fuse would blow, thus disconnecting the supply.

The reason why we are now stuck with no less than 13 different styles of plugs and wall outlets, is because many countries preferred to develop a plug of their own, instead of adopting the US standard. Moreover, the plugs and sockets are only very rarely compatible, which makes it often necessary to replace the plug when you buy appliances abroad. In Hong Kong, we use the British square plug, which has a fuse built into the plug (thus allowing it to be used with the ancient wiring in buildings in the U.K. which might not be fused properly). This plug has three rectangular prongs that form a triangle. British Standard BS 1363 requires use of a three-wire grounded and fused plug for all connections to the power mains (including class II, two-wire appliances). British power outlets incorporate shutters on line and neutral contacts to prevent someone from pushing a foreign object into the socket.

The British domestic electrical system uses a ring circuit in the building which is rated for 32 amps (6 amps for lighting circuits). Moreover, there is also a fusing in the plug; a cartridge fuse, usually of 3 amps for small appliances like radios etc. and 13 amps for heavy duty appliances such as heaters. Almost everywhere else in the world a spur main system is used. In this system each wall socket, or group of sockets, has a fuse at the main switchboard whereas the plug has none. This is a clever system, and much more complex than in most areas of the world.

This is the way things stayed through the end of WWII. In the rebuilding of Europe after the war, companies had an opportunity to rethink the design of electrical distribution from the ground up. Unfortunately, they ignored Tesla.

When the German company AEG built the first European generating facility, its engineers decided to fix the frequency at 50 Hz, because the number 60 didn't fit the metric standard unit sequence (1,2,5). At that time, AEG had a virtual monopoly and their standard spread to the rest of the continent. In Britain, differing frequencies proliferated, and only after World War II the 50-cycle standard was established. Big mistake!

Not only is 50 Hz 20% less effective in generation, it is 10-15% less efficient in transmission, it requires up to 30% larger windings and magnetic core materials in transformer construction. Electric motors are much less efficient at the lower frequency, and must also be made more robust to handle the electrical losses and the extra heat generated. Today, only a handful of countries (Antigua, Guyana, Peru, the Philippines, South Korea and the Leeward Islands) follow Tesla’s advice and use the 60 Hz frequency together with a voltage of 220-240 V.

Originally Europe was 120 V too, just like Japan and the US today. It has been deemed necessary to increase voltage to get more power with less losses and voltage drop from the same copper wire diameter. At the time the US also wanted to change but because of the cost involved to replace all electric appliances, they decided not to. At the time (1950s-60s) the average US household already had a refrigerator, a washing-machine, etc., but not in Europe.

The end result is that now, the US seems not to have evolved from the 50s and 60s, and still copes with problems as light bulbs that burn out rather quickly when they are close to the transformer (too high a voltage), or just the other way round: not enough voltage at the end of the line (105 to 127 volt spread !).

Note that currently all new American buildings get in fact 240 volts split in two 120 between neutral and hot wire. Major appliances, such as virtually all drying machines and ovens, are now connected to 240 volts. Americans who have European equipment, can connect it to these outlets. Unfortunately, as we found out when we moved to Hong Kong, which adopted British standards, you can't hook American appliances such as washers to 240 volt systems. This is because some of the electronics actually use 120 volts on these appliances (thus use the center tap) and others take the full 240 volt spread.


Blogger Jerry H said...

I agree with most of your comments but I think that Europe had standardized on 50 Hz and 220 Volts (now 230V) BEFORE world War II. AEG seems to have developed 50 Hz equipemnt and Siemens as the biggest elevtrical supplier in the world seems to have helped make 50 Hz the standard in Europe and most of the world. Berlin seems to have led the change to 220 volts in 1899 as Berlin was changing from dc to ac and didn't want to rewire what was already there and upped the voltage to 220 Vac. THis spread all over Europe and then the rest of the world. The US never changed from 110V (excepting the change in the 1950's to 120V) and I wonder if the residue of the Edison-Westighouse clash on AC-DC safety which had no counterpart in Europe prevented the US from going to higher voltages early in the 20th Century (not after world war 2) as Europe did.

4:46 AM  
Anonymous Nazish said...

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11:39 PM  
Blogger ic7401 said...

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12:58 PM  
Blogger ic7401 said...

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12:58 PM  
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11:14 PM  
Blogger teknik said...

Yes - that is true, hopefully with the advent of universal power supplies in many new appliances today, North America may have another chance at introducing 230 volts. A peoples movement to do this from the Split Phase would be good. Or from a State basis, an education campaign, and having the right rules that new appliances sold must be adaptable for 230 volts, and the right electrical safety rules... Also the Australian Power Point (outlet) was designed and used in the United states, but is now used also in China, some parts of South America, and other countries such as PNG, New Zealand and Fiji. It has the flat pins in a V-shape and a flat earth pin.

10:15 AM  
Anonymous Anonymous said...

It is "Nikola" not "Nicola".

4:28 AM  
Blogger SEM said...

Hi. Can you tell me why it's better for equipment to have a high voltage? I gather it is because then there is a lower current, but why is that better? Are there fewer fluctuations in the output? thanks.

2:02 AM  

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