High pitched noise in Siemens Desiros

[Domeyhead]

Hi, can an electrical engineer or fitter explain the cause or purpose of the high pitched warble which accompanies Class 444 and Class 450 units when they first pull away? I assume it is related to their initial acceleration and it seems to give way to a steady whine as soon as the unit gets above around 5mph.
ta!

 

[westcoaster]

Modern traction motors that's all

 

[Geezertronic]

Is that the same type of noise for the 350s too?

 

[westcoaster]

It is yes, I believe it's because they are iirc 3 phase AC motors, but I might be wrong

 

[O L Leigh]

It's actually the control electronics that make the traction motors work that make that noise.

Networkers and Cl323's use Gate Turn-Off (GTO) Thyristors which is why they sound like they're changing gear as they accelerate and brake using the regen brake. Newer stuff like Electrostars and Desiros use the next technical development called an Insulated Gate Bipolar Transistor (IGBT). It does the same job as a GTO Thyristor but uses less current, switches faster and can be made smaller and lighter. They also sound very different making more of a whining noise.

O L Leigh

 

[Domeyhead]

THanks Mr Leigh. I was wondering whether the "warble" was because power to the wheels was being "pulsed" on startup to reduce or prevent slipping, and this is why the note changes to a steady whine as soon as the unit is moving smoothly.
I guess I am also interested in how solid state equipment such as thyristors and transistors can generate so much noise without being distressed! I (probably wrongly) still associate noise with movement but the Desiro thyristors or gate noise seems exceptional compared to whatever kinetic effect must actually be occurring within the motor. It is exceptionally loud on pull away as all commuters in SWT territory know well.
I expect Roger Ford has done this at some point but I must have missed it!

 

[O L Leigh]

You could always have a read of this and see how much of it makes sense.

O L Leigh

 

[captainbigun]

It's not the devices as such which are responsible for the warbles. The change in pitch is down to the frequency of the carrier used for the PWM. You may note that the frequency used for the Desiros is audible and that used for the Pendos isn't. All down to manafacturer choice.

 

[TomJ93]

This noise has earnt them the name "Sci fi" trains by my uncle!

 

[ChampsRacing]

The reason why our 444/450s sound like that for is when we first got them, if you took full power from a standing start a warning used to come up on the TMS about the motors overheating and being burnt out so to stop this they employed that system so you can take full power on the handle but the software stops the motors going straight into full power.

 

[Kneedown]

This noise has earnt them the name "Sci fi" trains by my uncle!

I prefer the term "Jimmy Saville's"

 

[Goldfish62]

It's not the devices as such which are responsible for the warbles. The change in pitch is down to the frequency of the carrier used for the PWM. You may note that the frequency used for the Desiros is audible and that used for the Pendos isn't. All down to manafacturer choice.

And also the same on the Juniper - all you hear is the traction motors (but if you listen carefully there's a faint buzzing in the background).