What does a rectifier do in an EMU?

Question

Also, what is the difference between a Silicone rectifier and an air cooled retcifier. i.e . is one better than the other and why is this the case?

Thanks.

Answer 1

A rectifier converts AC to DC.

For high current applications, an air cooled rectifier helps.

You can have Silcon, Mercury arc, Germanium or other sorts of rectifiers.

Answer 2

There is no difference - the silicon you refer to is what the actual rectifier is made of. All the "air cooling" you mention is the method of cooling the rectifier down - rather like a computer with a fan.

Answer 3

EMU - Electric Multiple Unit.

The Pantograph (shown here: http://www.old-dalby.com/images/SAR_Pant... draws off the 25Kv power from the overhead cable's.

Electricity is then drawn into a Rectifier which converts the power to 650 - 750v DC. (Direct Current)

If the track has the typical 3rd rail layout, shoegear (shown here:  http://www.geocities.com/tubeprune/73-TS... which are located on the bogie with a pickup beam  pick up the current travelling though the non running rail then same procedure applies.

Answer 4

A rectifier converts AC to DC, a simple low power one can be built using 4 diodes, however the high voltages and currents involved would require more complex systems (ie the Silicon and Air Cooled - I'm afraid I don't know anything more about the technical side of these types)

In the train the recifier would have converted the 50hz AC current into DC for the motors. But newer trains feed the rectified DC into a frequency converter (a Variable Inverter - again I don't know the technical parts) which generates AC at various frequncies to drive Asyncronous motors.