History Re: [TCML] Kids class Project

[Ed Phillips]

The real big problem with HV DC lines is that they don't work with 
transformers.  You can use an AC xmfr from the generator and into the 
substation, jack up the voltage with an AC transformer, then rectify it 
with relative ease, and then transmit it at low loss over long 
distances.  The problem occurs when it gets to where it is going.  You 
can't use a transformer on a 750 kV DC line.  AC works fine with xmfrs 
but not DC, so you need a high voltage inverter to bring it back to 60 
Hz to operate on the local distribution legs and with the AC xmfrs at 
homes and factories.

Recently, with the advent of IGBTs and other transistorized devices, the 
power industry is coming around to using DC lines in certain applications.

Dr. Resonance"

    The "Pacific Intertie" between the northwest and Southern California 
is such a line.  First line was +/- 400 kV at about 1500 MW and more are 
planned.  Originally worked with thyratrons [ignitrons??] at the 
receiving end but now all semiconductor inverters.  In Tesla's time 
there was an experimental system in Europe which used series-connected 
DC genenerators to create "high" voltage DC with series-connected motors 
at the receiving end to convert the power.  Forget the name of the 
system but it was almost certainly never more than an experiment.

Ed