- #1
Crazymechanic
- 831
- 12
Hi , I observed an older type of electric train yesterday which is a DC train having a +ve overhead wire with around 3000v in it.
Now as I was sitting there I saw the capacitor banks below the train , probably used to smooth the incoming voltage for peaks and stuff to feed that further to the motors.
Now there are two things that come to mind , first one is usually a capacitor is charged using both + and - , in this case we have a +ve wire as the supply wire and then the whole train, chassis wheels and rails at ground potential.Now as far as where the power comes I understand , because of the +ve supply wire there is a potential difference but is that enough do charge a capacitor?
In other words if I would to take a capacitor and ground one plate while connecting the other plate at some + potential would that charge the capacitor?
I guess it should as the opposite charges from ground would flow towards the positive plate and the capacitor would charge right?
Also the other question that I have thought is what would happen in the case of an wire isolation breakdown , in other words if the overhead wire would somehow fall on the train chassis or just some train inner wire loose its insulation , the passengers inside the train wouldn't feel anything right ? Because firstly the whole train is grounded or at ground potential and the passengers are not part of a circuit and also because the train chassis forms a something similar to a faraday cage?
And even if one passenger would touch the train chassis while standing on ground , he would only feel a shock if the resistance through him would be smaller than that through the train wheels through rails to ground is that right?
Here is a link just for picture purposes of a similar train , an old dc train.
http://spoki.tvnet.lv/upload/articles/17/179646/images/_origin_Rigas-Vagonbuves-13.jpg
Now as I was sitting there I saw the capacitor banks below the train , probably used to smooth the incoming voltage for peaks and stuff to feed that further to the motors.
Now there are two things that come to mind , first one is usually a capacitor is charged using both + and - , in this case we have a +ve wire as the supply wire and then the whole train, chassis wheels and rails at ground potential.Now as far as where the power comes I understand , because of the +ve supply wire there is a potential difference but is that enough do charge a capacitor?
In other words if I would to take a capacitor and ground one plate while connecting the other plate at some + potential would that charge the capacitor?
I guess it should as the opposite charges from ground would flow towards the positive plate and the capacitor would charge right?
Also the other question that I have thought is what would happen in the case of an wire isolation breakdown , in other words if the overhead wire would somehow fall on the train chassis or just some train inner wire loose its insulation , the passengers inside the train wouldn't feel anything right ? Because firstly the whole train is grounded or at ground potential and the passengers are not part of a circuit and also because the train chassis forms a something similar to a faraday cage?
And even if one passenger would touch the train chassis while standing on ground , he would only feel a shock if the resistance through him would be smaller than that through the train wheels through rails to ground is that right?
Here is a link just for picture purposes of a similar train , an old dc train.
http://spoki.tvnet.lv/upload/articles/17/179646/images/_origin_Rigas-Vagonbuves-13.jpg