[GreenKeys] Teletype Motors

[Douglas W. Jones]

On Mar 9, 2010, at 1:02 PM, WB6BLV ((DM06)) wrote:

> interestingly, for  many years the speed and torque of railroad  
> locomotives was controlled, to some extent, by switching the pole  
> configuration of the wheel motors...   a large number of poles  
> would provide tremendous starting or low-speed pulling torque while  
> switching to a configuration of fewer poles would provide increased  
> speed once accelerating the load had been accomplished and   
> therefore less torque was required...

The idea is hardly a thing of the past.  Look, for example, at
-- http://www.chorusmotors.com/technology/index.shtml
Their "Technical show" is a decent tutorial on how they're doing
this today (a 17-pole induction motor, with 17 variable frequency
inverters driving it, with electronic synthesis of what the
railroads used to do with mechanical switches.

> more interestlingly consider the task of the railroad engineer,  
> who, before the era of automation, had to manually throw all those  
> high-amperage switches to alter the pole configuration of the  
> locomotive's wheel motors...   talk bout the need for speed and  
> dexterity....

But, of course, the engineer didn't throw the switches, he just
turned a control handle.  Inside the box below the handle was
a stack of cams that switched power to relays (contactors) that
switched the motor power configuration.  On DC locomotives, the
traction motors were put in different series and parallel connections
for different speed ranges.  On AC locomotives the effective number
of poles on the motors was changed.  The details of the cams inside
the controller and the details of the relay bank varied significantly,
but to the engineer driving the train, it was just "notch 1 for
starting -- do not stay in notch 1 for too long", then "notch 2
for low speed running", then "notch 3 for accelerating -- do not
stay in notch 3 for too long", then "notch 4 for high speed running."

The controller settings with time limits involved series resistors
to limit the winding current at non-optimal speeds.  At their best,
these wasted power.  At the worst, the motor itself was prone to
overheating in these settings, so you were only allowed a minute or
two of operation at these controller settings.

		Doug Jones
		jones at cs.uiowa.edu