🚀 go-pugleaf

ers1@cbnewsm.cb.att.com (eugene.r.schroeder) writes:
>In article <1jmre4INNfks@rave.larc.nasa.gov> kludge@grissom.larc.nasa.gov (Scott Dorsey) writes:
>>In article <1993Jan21.095254.62979@cc.usu.edu> slmdj@cc.usu.edu writes:
>>>He is an assistant city engineer for Adelanto, CA, and told me that the way
>>>their power is distributed to a large substation is Direct Current!  

>>They do it with silicon, believe it or not!  They have thyristor switches
>>taller than a man, and switch the DC.  This way, they can run DC on the
>>long lines at high voltage, which is advantageous since they get more
>>power over the same wire (since the limiting factor on the lines is the
>>peak voltage before arc-over, and the peak voltage on DC is also equal
>>to the average).

       Yes, there are thyristors that big.  First big power application
was a power line across the English Channel (submarine cable).  The
Continental and British grids aren't synchronized, and the proposed
tie wasn't strong enough to keep them synched, so they had to use DC.

       Thyristors are now available in sizes suitable for locomotive and
elevator power controls.  BART was the first rail system with solid-state
power controls, and it was a big headache in the early days.  Earlier
rail systems worked by switching motor windings around through various
series-parallel combinations, giving a limited number of speeds and
jerkey transitions.  There were, though, some "electronic" locomotives
in the 1950s that used ignitrons, which are a mercury-vapor device that
works like a thyatron or SCR.

       Have elevators all gone solid-state, or are systems with motor
generator sets still being installed?  Classical elevator control uses
a motor-generator set, with an AC motor and a DC generator, driving a
DC elevator controller.  The field current of the DC generator is adjusted
to control acceleration.  A generator has "gain" when used in this way.
This seems an obsolete approach, but there are certainly many still running.

					John Nagle