GTO thyristors... how do they work???

[ECML43]

Are there any electrical traction boffs out there who can give me a brief insight into the GTO thyristors (at least i think that's what they are) that you get on all modern electric traction systems. the only other online info i can find is on Wikipedia and thats hardly brief. what puzzles me is how they all make different noises.
try not to be too complicated in your answer...

thnks

[wyvern]

They switch the current on and off very rapidly for varying periods according to the average that is required. When the current required is high they will be on most of the time As the demand falls it changes 90% on 10% off, through 50% on 50%off, to 10% on and 90% off and so on.

The thyristor itself does not make any noise but the magnetic and electrical fields as the current passes through various components produces mechanical vibration at a frequency (or pitch) which will depend on the rate of on and off switching.

[ECML43]

thanks Wyvern, now i think about it that's pretty ingenious. but tell me... (if you know) why does the thyristor on the 3/465 EMUs appear to have several frequency build ups one after the other each sounding the same. the LU 1996 (jubilee line) stock does this too.

[wyvern]

Sorry, you need a mechanic for that one, but I think they use field switching as well.

This may help http://www.railway-technical.com/tract-02.shtml

[Flying Pig]

Originally Posted by ECML43

thanks Wyvern, now i think about it that's pretty ingenious. but tell me... (if you know) why does the thyristor on the 3/465 EMUs appear to have several frequency build ups one after the other each sounding the same. the LU 1996 (jubilee line) stock does this too.

Networkers have asynchronous AC motors (even though they're DC stock, which means they have to use Invertors to convert DC-AC).

So to accelerate the train the traction convertors increase the frequency of the 3-phase current going to the motors. Thats what the increasing frequency of whining is. The motors don't run at exactly the same frequency as the supplied current, they lag behind a bit, depending on the amount of torque applied.

HTH

FP (ex Networker driver who got sick and tired of the whining noise ).