A basic electrics question.

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swee'pea99

Squire
AC and DC transmission is interesting and something I am working on at the moment. Most power transmission is AC, but there are losses in the power lines due to the nature of the mutually generating magnetic and electric fields, leakage and partial discharge. DC transmission is much more efficient as the only factor to account for in Resistance (V=IR from schoolbooks). However only AC is generated, and all loads work on AC so you have to convert AC to DC, squirt it down the line and then change it back to AC at the other end. This conversion involves losses and with the present state of technology it is more efficient to transmit in AC for distances less than 1000km. High Voltage DC (HVDC) systems are used for transmitting power over long distances - for example in thr three gorges project in China where the supply is required 3000km away. HVDC is also used for power transmission under water where the permittivity of water is much higher than air leading to greater losses.The links between the UK and Europe are DC because they travel under water, and because if they were AC you would have to synchronise the phasing of the two systems.

AC to DC conversion is done in huge valve halls and is a bit more complicated than your basic rectifier bridge.

View attachment 378760

Each of the valves is built around a thyristor bank that is optically switched, I do the saturated reactors that limit the inrush current to the thyristors - they are the cast coil assemblies at each end of the valve. The whole footprint is about the same size as a caravan.

View attachment 378761

I realise my audience for this information is most likely limited to two people. :rolleyes:
But which is better to fry a horse, that's what the people want to know...

upload_2017-10-15_13-22-26.png
 

TVC

Guest
But which is better to fry a horse, that's what the people want to know...

View attachment 378772
QI covered this, Thomas Edison deserved a taste of his own medecine.

https://www.wired.com/2008/01/dayintech-0104/
 

subaqua

What’s the point
Location
Leytonstone
AC and DC transmission is interesting and something I am working on at the moment. Most power transmission is AC, but there are losses in the power lines due to the nature of the mutually generating magnetic and electric fields, leakage and partial discharge. DC transmission is much more efficient as the only factor to account for in Resistance (V=IR from schoolbooks). However only AC is generated, and all loads work on AC so you have to convert AC to DC, squirt it down the line and then change it back to AC at the other end. This conversion involves losses and with the present state of technology it is more efficient to transmit in AC for distances less than 1000km. High Voltage DC (HVDC) systems are used for transmitting power over long distances - for example in thr three gorges project in China where the supply is required 3000km away. HVDC is also used for power transmission under water where the permittivity of water is much higher than air leading to greater losses.The links between the UK and Europe are DC because they travel under water, and because if they were AC you would have to synchronise the phasing of the two systems.

AC to DC conversion is done in huge valve halls and is a bit more complicated than your basic rectifier bridge.

View attachment 378760

Each of the valves is built around a thyristor bank that is optically switched, I do the saturated reactors that limit the inrush current to the thyristors - they are the cast coil assemblies at each end of the valve. The whole footprint is about the same size as a caravan.

View attachment 378761

I realise my audience for this information is most likely limited to two people. :rolleyes:

Would I be one of them :smile:. They look like the DC rectifiers in one of the " cathedral" subs on the way out of Euston
 

TVC

Guest
Would I be one of them :smile:. They look like the DC rectifiers in one of the " cathedral" subs on the way out of Euston
Not sure where that one is, it's a stock photo from the Alstom (now GE) brochure. Seimens and GEC do similar systems.

Yes, you were part of my niche audience.
 

BrumJim

Forum Stalwart (won't take the hint and leave...)
Although I prefer my AC-DC-AC rectifiers and such like to fit into a box under a train, I still take an interest in transmission rectification, having worked for Alstom. A bit like the difference between an under-floor diesel engine and an Ultra Large Marine Diesel.

Count me in on the "interested" list.
 
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