how do electrics work?

[justanotheruser]

Hi all
My wife asked me an interesting question today. She ased if I could ever remember an electrical problem shutting down large sections of a train line in Sydney. I could not remember such a thing happening in my 20 years of using trains in sydney*. There certainly were signal and electical problems but there was a way for trains to keep operating on another track even if it was the same track for both directions. So why is it when there is an electrical problem between darra and goodna we have the chaos like last week where it took three and a half hours to get from ipswich to milton? Are the electrics in brisbane set up differently and in a way that prevents other tracks from being used?


*the only major electrical disruption I remember in sydney was when the short section of power lines shut down by police order prevented the trains leaving the sheds at the beginning of the day. (A man was threatening to jump onto power lines from enclosed bridge)

[STB]

Queensland uses AC power while Sydney uses DC power.  I'm not sure if this would have anything to do with it, other than with AC power they can isolate and shut down these sections, hence the lights and/or Air Con going out along parts of the network for a short moment, also allows trains to power up better with less substations than DC.

Other than that I don't completely understand how it works though.  Just a suggestion.

Someone should be able to explain it better.

[somebody]

I remember heaps of occasions in the early 90s that the power lines fell down at North Sydney and caused chaos in Sydney.  Now that they've completely replaced most if not all of the old wiring this shouldn't happen nearly as often.  I think it's just a case that Sydney's wiring is now newer than Brisbane's.

[mufreight]

With the 1500volt DC power supply in use in both Sydney and Melbourne there are shorter sections on the overhead and adjacent lines are fed through sectioning switchs allowing easier isolation of affected sections of overhead.
With the 25.000 volt AC electrification in use here the sections are longer and while the switching of power can isolate a section of overhead, safety issues relating to the higher voltage require the adjoining sections to be isolated also to avoid any possibility of a train running into the isolated section and energising the overhead of the section being worked on despite the overhead being grounded while work is carried out.
25 KVA AC requires a higher standard of insulation than 1500 v DC.
Hope that this helps a little.

[justanotheruser]

thanks for the replies very helpful.


just for the record i don't remember any problems with wiring at north sydney and I worked there for most of the 1990's. Of course with four platforms it may have been easier to get around and could be why.

[mufreight]

Of course part of the answer is called maintainence.
This would it seems be a new concept for QR Network which it would appear currently works on the basis of if it is not needed for coal or intermodal freight and it is still usable the policy is wait until it fails, then patch it up as cheaply as possible, instead of programed preventitive maintenance and when there are equipment failures, appropriate repairs instead of band aids.
Another reason why QR Passenger should be given full control of and responsibility for the commuter network as is the case in NSW.