What causes the whining sound when a BART train starts up?

Question

What causes the whining sound when a BART train starts up?

Answer 1

High horsepower ac electric motors make a whining noise when they start up...nature of the beast...

Answer 2

Depends on the drive equipment. Modern Electric trains make some strange noises. Eg the Desiros used by South West Trains make a noise similar to a Flying Saucer in a B-Movie

A couple of examples are in the sources.

The noise comes from resonating electrical equipment as the frequency of the Three-Phase voltage is changed to adjust the motor speed. I'm afraid thats the limit of my understanding of modern motor control systems.

Answer 3

BART trains use a Direct Current power source. The noise comes from Thyristors (also known as "Choppers"). These are solid-state electronics which convert direct current into alternating current at varying frequencies, hence the change in tone as the train accelerates. This can cause problems with signalling apparatus which use alternating current. (Many track circuits use a frequency of 83.33 Hertz because this is not a harmonic of 50Hz.)

Answer 4

Air brakes is a possible. If it is a diesel it could be a turbocharger. If it is electric it may be tight bearings on the motors. But if it is steam it may be a pressure valve releasing after it gets up to pressure. Here in Victoria (Australia) we have a "C Class" diesel locomotive that gives off a heavy diesel hum with a turbocharger whistling behind the hum. It sort of sounds like a jet engine revving up. WOW awesome!!!

Answer 5

I am guessing that it is air brakes releasing

*