High voltage dc

[nexium]

When we move into space there will be reasons for sending large amounts of electricity over a thousand kilometers or so. Three phase up to about 700,000 volts has been the upper limit for 90 years or so. Now an underwater cable will carry up to 3 gigawatts at perhaps three million volts dc at 1000 amps in the North Sea (north of England)<br /> There are several practical ways to produce three million volts dc, but how do you run refrigerators and hair dryers from three million volts? We can connect a million applances in series parallel, and have computers switch an applance every few seconds to a different leg or branch to keep approximately the correct voltage. Avoiding a leathal voltage above ground will be difficult, if not impossible, even if the system is grounded nowhere except though the human being electrocuted.<br /> We can connect 60 big dc motors in series, each designed for 50,000 volts. Each motor turns a three phase alternator which feeds the present 60 hertz grid. We may have to use more than 60 motors if 50KV proves more than practical. 70% efficiency is about the most we can hope for because of the very high dc input to the motors. Repairs to the motors will be dangerous unless the entire series string is shut down. Perhaps robots can do the repairs. Keeping the loads equal on the 60 alternators is almost as challanging as juggling appliences in the series parallel network.<br /> We can scale up the tuning capacitor as used in AM radios. At minimum capacity we charge the capacitor to 3 million volts. It stores one watt second. We now rotate the capacitor so the plates mesh, increasing it's capacitance by 100 times. the voltage drops to 30,000 volts which is much more managable. We are still storing one watt second. We can repeat this perhaps 60 times per second with 100 variable capacitors thus steping down the dc voltage at the rate of 6000 watt seconds per second = 21,600,000 watt seconds per hour = 22 megawatt hours per hour, if I did the arithmet

 

[bobw]

Inverters?<br /><br />I went on a tour of a little hydroelectric plant in Estes Park, Colorado. They have a series of dams and little lakes connected by tunnels to get energy from the same water over and over again. The cable that carried the electricity from the plant, 3 phase, was only about 4 inches in diameter but they had it in a conduit that they pumped high pressure nitrogen into to keep it dry and insulated. I'd be interested in the physical design of a 3 million volt underwater "cable". I bet it is more than just wire. <div class="Discussion_UserSignature"> </div>

 

[igorsboss]

Use the DC power to electrolyze seawater, then bottle the H2 to jumpstart a new hydrogen economy.

 

[bobw]

I don't know if that is a good idea. When I was very young I tried the electrolize thing with my chemistry set. The bubbles weren't forming very fast so I put in some salt to get better conductivity. I took a big sniff of my oxygen test tube and it was full of chlorine. I thought I was going to die. Pure oxygen might smell like that but I don't think so. Electrolize fresh water only <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[glutomoto]

Re: underwater cable will carry up to 3 gigawatts at perhaps three million volts dc at 1000 amps in the North Sea (north of England) <br /><br />That much d.c. voltage is not and never was intended for the consumer. It is just used for the long distance transmission of electricity, because d.c. is cheaper than a.c. for the long distance.<br /><br /><hr /><br /><br />Re: When we move into space there will be reasons for sending large amounts of electricity over a thousand kilometers.<br /><br /> Now if your talking about transmitting energy say from L5 to the moon. That can't be done with wires, but I hear microwaves can make it happen.<br /><br /><img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[siarad]

Don't know to which you refer but DC is used between here & France for basically two reasons:<br />Lower insulation, say 100VAC would need 142V insulation<br />to enable the correct phase on connexion to AC by inverters. It would be impossible to change every generator in a country to correct phase.

 

[vogon13]

I seem to recall a similar transmission line in the U.S. and they use the DC power to run a hulking big DC motor that turns a 3 phase AC generator. <br />Then of course, you could have some transformers and outlets and plug in your Okama Gamesphere. <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[pocket_rocket]

You could always use it to charge 250,000 car batteries. lol

 

[nexium]

Everyone made interesting comments. I considered almost that many12 volt car batteries in series to harness lightening. Robots could remove 18 batteries at a time to provide about 230 volts dc to run most home and business devices. The robots would then put 19 partially discharged batteries back in the series string. Near the end of their useful life, batteries return less than 1/2 the charging kilowatt hours, so the efficiency would be low and replacing marginal batteries would be a major over head cost by the third year.<br /> Transformers require ac, but rotary switches have been used to chop dc into square waves which will work marginally in transformers, but I don't think the idea has been tested over about 100,000 volts dc input. The converter of this sort would make lots of radio noise which is costly to surpress and the contacts need frequent replacement.<br /> Solid state inverters can be designed for up to about 1200 volts dc input. Is any one aware of commercially available inverters for more than 1200 volts dc input? Neil

 

[nexium]

Electrolysis cells need 2 or 3 volts each, but it may be practical to wire a million of them in series. Lots of low cost hydrogen available, would definately stimulate applications for hydrogen. I think hydrogen can easily supply 1% of the world's energy, which is a large scale up from present usage. The electrolysis cells convert about 1/2 of the energy to low grade heat, which could provide a warm water utiliy in a test community. A third faucet that supplied instant warm water would be a big plus in my opinion. Neil

 

[hayagreeva]

underwater cable.. 3 gigawatts at three million volts dc (1000 amps) in the North Sea (north of England) <br /><br />Incredible feat- As a Highvoltage Engineer with HV DC background, I consider it a a tremendous break for a neglected field over a century.<br />