Re: [NSW] Power of V-set traction motors

[usenet.spam@gunzel.net (Michael)]

Tom <gunzel3801@optusnet.com.au> wrote in article
<3adb9853$0$25472$7f31c96c@news01.syd.optusnet.com.au>: 

>So what are the difference betweem chopper motor sets and camshaft?

Camshaft control is power control by means of resistance grids. AFAIK, the 
camshaft itself will set the contactor to set the resistors up in series, 
series/parallel, parallel, which in turn varies the voltage being applied 
to the traction motor. 

Chopper control uses a thyristor to apply a constant voltage to the 
traction motor, but chop it up into on/off cycles. For lower speed, the 
power applied to the motor is on less than it is off, medium speed, the 
power would be chopped approx 50/50 (i.e. on 50% of the time, off 50% of 
the time). At a certain point, the chopper will cut out and you will have 
full DC being applied to the traction motor. 

Chopper has a number of advantages in both efficiency and passenger 
comfort. In efficiency, a lot is lost in the resistance grids (heat energy) 
on a camshaft control. In passenger comfort, you do not get the jerkyness 
of the series -> series/parallel -> parallel transitions in a chopper 
controlled train. Chopper control is generally computer controlled and 
allows for smooth transition of power application.

Hopefully this is clear and correct, if not, someone else can correct me (:

M.


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