20-04-2017, 07:29 AM
In the early days of electricity there was "the battle of the currents" with Edison behind DC and Westinghouse/Tesla behind AC. It was a pretty dirty war. The Edison DC model relied on numerous local power stations as there was no practical way to step up the voltage for economic transmission over long distance. Inevitably the Westinghouse/Tesla AC system won. As demands grew, town centre power stations became impractical so HV transmission was essential. In London Ferranti's Deptford power station was the pioneer project. Only possible then with AC.
The 3 phase system also gave simple and rugged motors and generators. However DC was still needed for motors (notably traction motros) that needed fine control, also for arc lighting. Hence DC mains available alongside AC for many years. I can remember DC at my late father's factory in Bishopsgate to supply the lift motors. That would have been there until at least 1970. Hence motor generator sets and mercury arcs. London Underground used large numbers of steel tank MARs.
Now it's all possible with DC. In certain cases such as data centres the main power distribution can be DC, thus simplifying the power supplies and reducing losses: http://www.datacenterknowledge.com/archi...fficiency/
The problem with 115V, AC or DC, is still the heavy cables needed. Others have mentioned electric kettles, toasters etc. For 2kW+ you really want 230V. For supplies to houses you need the US model of one transformer for every few houses. Might be feasible with DC distribution. Something like a 1000V DC local network fed from substations every few blocks and a small DC-DC converter for each house.
While it's fun to speculate it won't happen in the near future - plant and cables have very long lives. Much of today's work in local distribution is concerned with the effects of embedded generation such as PV. Keeping the voltage stable under these conditions brings new challenges.
A little obscure point. I once bought an Ekco AC74 console set in a junk shop. An ugly lump with a wooden cabinet and the same bakelite grille as its collectable cousins. Except it was a DC74. And not just a DC74 but a special variant of the DC74 with extra main filtering for areas where the supply was from MARs. So don't assume that DC mains will be nice and clean. There may not be hum but there will be loads of switchmode rubbish on it.
The 3 phase system also gave simple and rugged motors and generators. However DC was still needed for motors (notably traction motros) that needed fine control, also for arc lighting. Hence DC mains available alongside AC for many years. I can remember DC at my late father's factory in Bishopsgate to supply the lift motors. That would have been there until at least 1970. Hence motor generator sets and mercury arcs. London Underground used large numbers of steel tank MARs.
Now it's all possible with DC. In certain cases such as data centres the main power distribution can be DC, thus simplifying the power supplies and reducing losses: http://www.datacenterknowledge.com/archi...fficiency/
The problem with 115V, AC or DC, is still the heavy cables needed. Others have mentioned electric kettles, toasters etc. For 2kW+ you really want 230V. For supplies to houses you need the US model of one transformer for every few houses. Might be feasible with DC distribution. Something like a 1000V DC local network fed from substations every few blocks and a small DC-DC converter for each house.
While it's fun to speculate it won't happen in the near future - plant and cables have very long lives. Much of today's work in local distribution is concerned with the effects of embedded generation such as PV. Keeping the voltage stable under these conditions brings new challenges.
A little obscure point. I once bought an Ekco AC74 console set in a junk shop. An ugly lump with a wooden cabinet and the same bakelite grille as its collectable cousins. Except it was a DC74. And not just a DC74 but a special variant of the DC74 with extra main filtering for areas where the supply was from MARs. So don't assume that DC mains will be nice and clean. There may not be hum but there will be loads of switchmode rubbish on it.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
