London Banter - View Single Post

Colin Rosenstiel · September 8th 04, 12:29 AM posted to uk.transport.london

In article ,
(Neil Williams) wrote:

If the electric motors are of the three-phase type often employed on
recent[1] rail stock, the "gear change" is actually a change in the AC
frequency being applied to the motors as they speed up. It (put
simply) has broadly the same effect as a gear change, but no physical
"gear" is being "changed" as such.

[1] While all EMUs built since the 1990s have this technology, it's
not always audible for various reasons. The Class 323 EMUs used in
the Manchester area seem the most obvious.

ITYF that the noise is more pronounced on older three phase designs.
Current production uses a later three-phase technology which has a less
pronounced "gear change" effect.

--
Colin Rosenstiel