Polarity of 750Vdc electrification

[Bald Rick]

Returning to Euston, the entire station and it's approaches were equipped with axle counters in the 1990s resignalling so track circuit compatibility with the two electrification systems is not an issue.

That's odd. I must have dreamt commissioning all those HVIs and TI21s in the summer of 2000 then. Very realistic dream though.

 

[Philip Phlopp]

That's odd. I must have dreamt commissioning all those HVIs and TI21s in the summer of 2000 then. Very realistic dream though.

Involvement in WCRM and not talking about nightmares. You're weird.

 

[hwl]

Involvement in WCRM and not talking about nightmares. You're weird.

The dream wasn't referred to in either a positive or negative (nightmare) sense but a neutral one.



(I'll get my coat )

 

[MarkyT]

That's odd. I must have dreamt commissioning all those HVIs and TI21s in the summer of 2000 then. Very realistic dream though.

I bow to your superior local knowledge. I was told years ago it was all axle counters and just accepted that without checking. Having looked at the sectional appendix now, it appears axle counters first appear through Primrose Hill and Kensal Green Tunnels, then after track circuits through the Wembley complex they resume once again just north of there all the way to and beyond the LNW south sectional appendix boundary at 119m 20ch.

For those who don't know, the track circuit types Bald Rick mentions are both dual immune, so can be used in AC, DC and dual system electrification areas.

 

[HSTEd]

750V nominal wiring would be able to support a Type 1 equivalent, which means that if we can solve the feeding issues we could potentially generate a low performance general railway on the Swiss model with relatively low capital costs.

Such a thing will need ongoing subsidy, but with the outlook for fossil fuel phase out it is worth bearing in mind.

It is really annoying that the RSSB will simply not allow a 1500Vdc tramway.
It would make trams far more economic to engineer and operate.

EDIT:

It is also worth noting that if the vehicle has a main circuit breaker between the pantograph and traction electronics that you could simply have a DPDT contactor after the circuit breaker.
When the voltage on the line drops out of spec, like in a neutral section, the main breaker opens, disconnecting it from the line.
When the line voltage returns you can use a pair of anti parallel diode protected relays to determine which polarity it is. The contactor can then be set appropriately and the breaker brought back in, hopefully all in a second or less.