Traction Motors.
 

Having worked on the West Coast Main Line, as I did, and in the days of 84s, 85s, 86s and 87s and the 310 units which used to be on there, and living close to that line today , I hear the trains all day and night. But I know very little about todays modern electric traction....having said that when I listen to the Traction motors of some trains, they always seem to be "screaming", it is hard to describe really, but are the modern traction motors a lot different to the ones in the 70s and 80s ?
Perhaps someone who knows about todays trains can tell me ?

48111

Sorry Peter i cant answer you question on traction motors i wouldnt think they have changed all that much from the older motors but who knows.
I remember the 37s fitted with new motors a lot lower gearing for greater loads also the maximum speed was dropped from 90 to 80mph.

ccmmick.

Probably the difference between DC and AC motors and their control
systems
Or as someone wrote about the traction motor control
box " Here be majik"

Definitely AC motors so they dont have brushes and the speed is determined by the frequency of the applied voltage hence the screaming. As the motor speeds up the frequency changes in steps which are computer controlled. The driver just selects GO.

I was wondering if, The maintenance companies, actually kept some of the traction motors off the AC "leccys" that were scrapped ?

48111

Well strictly speaking it's still a notched controller as before.

So for example a new class 377 with AC motors has 4 notches of power and 4 steps of brake (3 plus Emergency) exactly like an old Class 319 with DC motors.

The 319 has two old fashioned handles, whilst the 377 has the more modern Combined Power & Brake controller.

But you drive each unit in exactly the same way (and as you would expect the 377 is just a little smoother & quicker - usually).


In fact AC motors have just about taken over nowadays, even Locos are getting them (Class 70). One advantage they have over DC motors is the ability to provide Dynamic braking, which is more effective (at speed) than friction brakes, and it saves on brake pad wear.

brake dust
 

And there is no more brake pad dust to drift absolutely everywhere especially on a windy day.:p

The normal method of controlling DC traction motors on units 304-321 was to use resistances, and or tap changer controlled by the cam shaft in the motor coach. There may also have been a form of field divert which controls the back EMF in the motor field windings
Electric locos had a form of tap changer control, this is tappings off the secondary windings of the main transformer. More modern locos class 90/91 use power electronics to control the motors. In the simplist form the control units compares a referance signal generated by the drivers power control handle to the speed of the vehicle. In either case the speed of the motors is controlled by changing the input voltage.
AC motors need electronic control as if you change the voltage of AC current you also change the frequancy. This can cause damage to the motors, so the electronics manage the frequancy to keep a more constant signal.
In real life the power control handle will show power steps, this is only a guide to the driver as the contol equipment is stepless. This is what gives a smoother ride, and has the advantage of preventing wheel slip in poor conditions