Re: super series wheelslip control

[matthew@mail.usyd.edu.au (Matthew Geier)]

In article <FhFr6.3094$zW2.131764@ozemail.com.au>,
Chris Downs <cvdowns@ozemail.com.au> wrote:
>
>Always thought this'd be perfect for a retro-fit on V-sets, no creep of
>course, just match the power to stop wheel slip.
>
>For anyone in the know how does G7 (CityRail's AC motored set) deal with
>wheelslip compared with DC motored sets?  And of course what are the
>Millennium sets going to use (same as G7)

 It doesn't. The AC motor's rotational speed is directly controlled by the
frequency of the input power. An AC induction motor as used in these
applications can not spin out of control like a DC traction motor can, the
most it can do is lose the 'slip angle', which is only a few degrees, and
the smaller the 'slip angle' the lower the torque, so that will naturaly
fix it self anyway. (If the wheel starts to slip, the 'rotor' starts to 
'catch up' with the rotating (controled) magnetic field, the closer it gets
to perfect lock, the less the torque the motor generates so the less likely
it is to keep slipping at the railhead). If the controler says do 10RPM, the
motor does 10RPM, load or no load. (With in limits of course, you could always
load it until it stalls... :-)

 This problem with 0 torque at 1:1 magnetic fields between the rotor and the
stator is what made induction motors unsuitable for traction applications
until the advent of cheap microprocessor controls that can fiddle with the
motor coils and process the feedback as appropiate to get torque.

 The AC induction motor is mechanicly simple, the complexity is in the 
electronics that drive it. But the complex electronics is in an easly
field replaceble box and can be built to self diagnose. The motors that
need a heavy workshop to repair have a low parts count and don't need
as much maintence.

 They would be absolutely nuts not to fit VVVF AC drives to the Millennium
sets. The technology is pretty proven now. Lower maintence costs and lower
energy consumption.

 You could calibrate the throttle in kph on an AC motored train. Probably the
only reason G7 isn't calibrated like that is 1/ the drivers expect a 5 notch 
'power' throttle not variable 'speed', 2/ it has to interoperate with DC
motored sets. (Although they are call 'chopper' controlled, so their power
controlers could be recalibrated to 'variable speed' as well, the traction
management computer varying the power as appropiate).