Johnny B Good wrote:

On Mon, 24 Apr 2017 12:44:26 +0100, Mike Clarke wrote:

I think they used to run pairs of motors in parallel on starting and
switch over to series at higher speeds. That was some time ago and I
don't know if they still do.

If true, the sequence would have been series for starting, then
paralleled for 'cruise speed'. Effectively a two speed "Electric Gearbox"
created out of nothing more sophisticated than a cleverly sequenced bunch
of contactor switches.

It is quite true, though the actual method is somewhat more
complicated. I was about to start writing a description, but it
is covered rather well he

http://www.railway-technical.com/tract-01.shtml

About the last UK stock to be built using this principle was the
1983 Tube Stock which was retired from service comparatively
early in 1998. Older examples are still in daily use.

Chris
--
Chris J Dixon Nottingham UK


Plant amazing Acers.