Re: Impressions of the Gold Coast line

[jjjim <jjjim@bigpond.com>]

yes ,  It is used that way in Cordless drils too, Little wasted energy as aposed to
a resistor  But also used in AC motor control to alter the frequency of the
current,  keep in mind AC motors  are controlled by frequency. torque versus speed
characteristic can be changed thru frequency change  So i take it everyone uses the
term inverter for the above,  and chopper for modern DC control,   Fair enough :)

David Johnson wrote:

> Chris Downs wrote:
>
> > I thought a chopper literally chopped the current off for a short period of
> > time and this was done many times per second.  More current's chopped out when
> > starting giving the same effect as burning "excess" current with resistors.
> > As the train accelerates the chopper stops current for shorter periods of time
> > (like switching through resistors) until the point is reached where continuous
> > current flows, i.e. the chopper is off.
>
> A chopper is a Gate Turn Off Thyristor.   A normal Thyristor only turns on, then
> switches off when the voltage reaches 0.  As DC doesn't turn off, the GTO
> thyristor is used, which turns off when remove the voltage from the Gate.
>
> I think that is basically accurate, correct as necessary. :)
>
> --
> David Johnson
> trainman@ozemail.com.au
> http://www.ozemail.com.au/~trainman/
> ------------------------------------
> These comments are made in a private
> capacity and do not represent the
> official view of State Rail.
> C.O.W.S. Page 11.