I'm kindly disagreeing, because I think we are misunderstanding each other.
It can't be the traction equipment because it is uniform whether the train is accelerating softly, fully, or whether it is at a stand.
Then I'm afraid you've confused the hell out of me.
I initially thought that you were referring to an "always on" background hum, but had been persuaded by your later posts that you were not. Which is it?
In either case, here is a list of the various hums one might hear on a Cl314 together with their causes.
1) Transformer - This is a constant hum that neither rises nor falls in pitch nor, it would appear, change in volume. The primary cause of this hum is actually not electrical but mechanical. It's the oil pump that keeps the transformer cool. As the transformer lives under the centre car, this is where it will be heard.
2) Rectifier - Like the transformer, this is a constant hum that you may hear in the centre car. However, the rectifier doesn't tend to be very loud.
3) Traction Equipment - This can be a very loud hum that neither rises nor falls in pitch. However, the volume can change dramatically depending on the power notch being used by the driver, with peak volume in notch 3 or 4. On a Cl314 the traction equipment is under the outer cars.
4) Motors - This hum rises and falls in pitch with the motor revs, though interestingly they don't seem to be any louder in a high notch than in a low one. Most of the noise is actually mechanical from the permanently meshed final drive gearbox and motor bearings, as the motors will continue to whine even when coasting. The motors are together with the traction equipment under the outer cars.
5) Heating - This is a constant background hum heard throughout the train. Cl314's don't have convection heating but instead circulate warm air through the vents between the seat backs. This requires fans.
Both the class 314 and 318 made the buzzing sound whether still or when accelerating in the centre car. Only the 314 made the buzzing sound at the front when accelerating. The 318 is silent. That's what I was trying to say. Also, the 318 middle car was a HELL of a lot louder than the 314. I could hear it over my iPod.
This is the difference between the two classes. A Cl318 has it's transformer, rectifier, traction equipment and motors all together under the centre car with the outer cars being trailers. The Cl314, by contrast, spreads it's electrical equipment around with only the transformer and rectifier under the centre car and the traction equipment and motors under the outer cars.
A Cl314 is formed Motor-Trailer-Motor while a Cl318 is Trailer-Motor-Trailer.
Well, if you remember back to this video:
http://www.youtube.com/watch?v=_owHcwQ89oY from the 22 second mark there's that loud buzzing sound that sounds like a big bumble bee in your ear.
There are two sounds on that clip. The loud constant buzz is the traction equipment while the whine that rises in pitch is motor noise.
I am 100% certain it is the AC power because when the train goes over a dead section, the buzz cuts out, only to cut in again when the dead section is over a second or two later. This is in the centre cars of the trains, under the pantograph.
When a unit goes through a neutral section, the VCB opens which isolates the entire train from the pantograph down from the overheads. When this happens, everything that runs directly from the transformer cuts out. About the only things that don't cut out are the control circuits and the lighting, which is run temporarily from the 110V DC auxilliary supply (batteries, essentially). Even the heating fans stop.
As far as the AC power goes, it comes down the HT cable to the transformer. All of the train systems use DC power except for the secondary circuits providing heat and light, and these run at 240V AC the same as your domestic household supply.
This sound that I am talking about, is clearly caused by the flow of electricity and the 60Hz hum that it causes by reverberations of the electrical equipment. It's the same sound caused by a ground loop or that you may hear at an electricity substation.
Leaving aside that the overheads provide power at 50Hz not 60Hz, comparing the sound of a unit to an electrical substation is meaningless. The power levels are massively different, as are the uses. You only have t compare the difference in size of the transformers to see that.
In any case, as I said before, a lot of the noise transformers generate is caused by the oil pump.
I hope I don't sound patronizing, or an a**hole, but I am really bad with my words, and I know what I am trying to say, it's just coming out all wrong. When I get my camera, I will just record all of the sounds that I mean, and then show you. But, I am convinced (so much I would put my house on it) that the sounds I am describing are purely caused by AC electrical reverberations and not the traction equipment which to me is more of a scream than a hum.
Maybe I am the only one who hears this immense hum that nearly all electrical equipment makes because I have hypersensitive ears...?
I don't think you're being patronising or arrogant. We're just having a chat.
However, at the risk of appearing both of those things myself, I do "sign" electric units and am very familiar with the virtually identical Cl315 units. In order to do my job I have to be technically competent and have a good understanding of how these trains work. Therefore I do have a pretty good idea what I'm talking about.
Regards
O L Leigh
