Engines / transmission for electric multiple units

[GJEdmunds]

I'm curious about the London Midland trains which serve the cross city line between Redditch and Lichfield. When they set off they make a noise which sounds as if they are going through very many gears, like an automatic.

What type of engine and what type of transmission do these trains have? I'd like to learn how they work.

 

[507021]

I'm curious about the London Midland trains which serve the cross city line between Redditch and Lichfield. When they set off they make a noise which sounds as if they are going through very many gears, like an automatic.

What type of engine and what type of transmission do these trains have? I'd like to learn how they work.

Electric multiple units don't have engines, they use electric motors which power the driving axles.

 

[375610]

Hi, the trains are a Class 323. They are electric multiple units that have a single-phase AC input (25kV, 50hz) that powers three-phase AC motors via a Variable Voltage Variable Frequency (VVVF) drive of the Gate Turn-Off Thyristor (GTO) variety. The switching frequency of a GTO Thyristor is limited and so as the speed of the motor increases the GTO has to change back to a lower frequency with a longer pulse several times, thus the 'gear changing' noise.