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Hot wires

 

Pushing a current through a conductor requires energy.  The difficulty in doing this is called resistance; and is measured in Ohms.  For each Ohm of resistance an electromotive force of 1 Volt is required to cause a current of one Amp to flow.  In other words Resistance = Voltage (drop across the conductor) divided by the current (Amps) in the conductor.  This is called Ohms law and is obvious, a priori, from the definitions of these quantities.

The important things to know about conductors are that: resistance varies depending on the material that the conductor is made from; and the electrical energy used to overcome resistance becomes heat. Read More...

Electrical conductors get hot depending on the current flow; and the heat generated goes up exponentially as the current increases in a wire.

Suppose the lead to a power board in your kitchen is carrying 2 amps and consuming 5 Watts per metre as heat.  This is so small you don’t even notice the lead getting warm. If you add a few more appliances taking the total to 10 amps the heat in the lead will jump, not to 25 watts per metre as you might expect (5x5), but all the way up to 125 watts per metre; at which point it will probably burst into flames. This is why commercial power boards have a big safety margin with wires around twice as heavy as those in this example; so there is only moderate heating even at 15 amps.

Resistance falls as conductors get fatter, in proportion to cross-sectional area. This is obvious because two identical conductors (or water pipes) side-by-side carry twice the current of one.

You may have noticed that the cord to some high current appliances, like heaters, kettles and vacuum cleaners, gets warm.  To avoid heating the wires in your house too much and possibly burning it down, properly installed wiring has current ratings well above a safe limit; electricians are careful that all strands of a cable are terminated; and the current is limited by fuses and other kinds of current breakers. 

 

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We often want some wires in home appliances to get hot:  electric heaters, kettles, toasters, and so on work on this principle; an incandescent light bulb generates so much heat that the filament glows white hot; a fuse wire melts if the current gets above a certain limit.

But unless you want a bit of extra warmth, heating wiring in buildings is wasteful and a fire risk.  It is particularly wasteful in the street or in wires running for miles in the country.  Many millions of kilowatt hours of electricity can be lost heating the countryside.

The actual losses are equivalent to approximately 10 percent of the total electricity transported between power stations and market customers.  In long links and in those carrying high currents, from time to time, the losses can be much higher than this.

 

 

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Travel

South Korea & China

March 2016

 

 

South Korea

 

 

I hadn't written up our trip to South Korea (in March 2016) but Google Pictures gratuitously put an album together from my Cloud library so I was motivated to add a few words and put it up on my Website.  Normally I would use selected images to illustrate observations about a place visited.  This is the other way about, with a lot of images that I may not have otherwise chosen.  It requires you to go to the link below if you want to see pictures. You may find some of the images interesting and want to by-pass others quickly. Your choice. In addition to the album, Google generated a short movie in an 8mm style - complete with dust flecks. You can see this by clicking the last frame, at the bottom of the album.

A few days in Seoul were followed by travels around the country, helpfully illustrated in the album by Google generated maps: a picture is worth a thousand words; ending back in Seoul before spending a few days in China on the way home to OZ. 

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Fiction, Recollections & News

The Time Lord

 

 

 

For no apparent reason, the silver haired man ran from his companion, shook a tree branch, then ran back to continue their normal conversation. It was as if nothing had happened. The woman seemed to ignore his sudden departure and return.

Bruce had been stopped in peak hour traffic, in the leafy suburban street, and had noticed the couple walking towards him, engaged in good humoured argument or debate.  Unless this was some bizarre fit, as it seemed, the shaken tree branch must be to illustrate some point. But what could it be?

Just as the couple passed him, the lights up ahead changed and the traffic began to move again. 

Read more: The Time Lord

Opinions and Philosophy

Renewable Electricity

 

 

As the energy is essentially free, renewable electricity costs, like those of nuclear electricity, are almost entirely dependent on the up-front construction costs and the method of financing these.  Minimising the initial investment, relative to the expected energy yield, is critical to commercial viability.  But revenue is also dependent on when, and where, the energy can be delivered to meet the demand patterns of energy consumers.

For example, if it requires four times the capital investment in equipment to extract one megawatt hour (1 MWh) of useable electricity from sunlight, as compared to extracting it from wind, engineers need to find ways of quartering the cost of solar capture and conversion equipment; or increasing the energy converted to electricity fourfold; to make solar directly competitive.

Read more: Renewable Electricity

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