Electrifying the Snow Hill Lines: Tram Interference

[Mordac]

I'm not sure if this fits here or in speculative discussion, if the latter, I apologize and ask the mods to move it there.

As per the title, if the Snow Hill lines were to be electrified, would there be problems because of the long sections where the tram runs parallel? The tram of course is electrified at 750V DC, and I know this can cause some issues when too close to 25kV AC.

 

[snowball]

There are other places where it happens: Edinburgh trams run alongside the Glssgow line for a considerable distance west of Haymarket. Manchester Metrolink runs alongside the line from Victoria towards Miles Platting, and alongside an electrified part of the CLC Warrington line which is wired as far as Trafford Park. The signalling systems would have to be checked for the correct immunities.

 

[Halish Railway]

I think the most appropriate case of this is to the North/East of Manchester Victoria, where the Metrolink effectively uses the old fifth and sixth tracks of the station throat, hence there is 25kV AC and 750V DC wires on adjacent tracks.

 

[Bald Rick]

I'm not sure if this fits here or in speculative discussion, if the latter, I apologize and ask the mods to move it there.

As per the title, if the Snow Hill lines were to be electrified, would there be problems because of the long sections where the tram runs parallel? The tram of course is electrified at 750V DC, and I know this can cause some issues when too close to 25kV AC.

No, because the return current flows for a 750v DC tram are a small fraction of the return current flows of a 750v DC train. The signalling on the main line is already ‘DC immune’.


This is the same reason why DC operation of the London Overground services on the same tracks as various AC services between Euston and Camden isn’t much of a problem (4 trains an hour, 4-5 coaches), whereas in the Thameslink core it is (up to 21 trains an hour, 8-12 coaches).

 

[Mordac]

No, because the return current flows for a 750v DC tram are a small fraction of the return current flows of a 750v DC train. The signalling on the main line is already ‘DC immune’.


This is the same reason why DC operation of the London Overground services on the same tracks as various AC services between Euston and Camden isn’t much of a problem (4 trains an hour, 4-5 coaches), whereas in the Thameslink core it is (up to 21 trains an hour, 8-12 coaches).

This is interesting is that because the tram is so much lighter?

 

[Bald Rick]

This is interesting is that because the tram is so much lighter?

Yes lighter, and lower speeds. The trams’ max power draw is roughly a quarter of that of a 5 car Class 720, for example, and the tram will draw full power for a few seconds at most at any given time.

 

[twpsaesneg]

No, because the return current flows for a 750v DC tram are a small fraction of the return current flows of a 750v DC train. The signalling on the main line is already ‘DC immune’.


This is the same reason why DC operation of the London Overground services on the same tracks as various AC services between Euston and Camden isn’t much of a problem (4 trains an hour, 4-5 coaches), whereas in the Thameslink core it is (up to 21 trains an hour, 8-12 coaches).

There are, of course, the stray current and touch potential issues, for which suitable mitigations must be put in place. The Network Rail OLE structures in the area of the Metrolink outside Manchester Victoria have insulating material which electrically isolate the foundations from the steelwork, and some masts have shrouding for touch potential. There also needs to be careful interface control between the two operators, it's a bit easier when it's Dual Voltage on NR infrastructure alone!

 

[Bald Rick]

There are, of course, the stray current and touch potential issues, for which suitable mitigations must be put in place. The Network Rail OLE structures in the area of the Metrolink outside Manchester Victoria have insulating material which electrically isolate the foundations from the steelwork, and some masts have shrouding for touch potential. There also needs to be careful interface control between the two operators, it's a bit easier when it's Dual Voltage on NR infrastructure alone!

yes, of course. I would expect that sort of stuff to be sorted at implmementaion - quite straightforward. I didnt regard it as a ‘problem’ in the context of ongoing issues, as seen in the Thameslink core. Sorry for not making that clear.

 

[Mordac]

yes, of course. I would expect that sort of stuff to be sorted at implmementaion - quite straightforward. I didnt regard it as a ‘problem’ in the context of ongoing issues, as seen in the Thameslink core. Sorry for not making that clear.

Would this add significantly to costs?

 

[Bald Rick]

Would this add significantly to costs?

no

 

[172007]

The one area which may be a little difficult may be the quarter of a mile from the Jewellert Quarter towards the Hawthorns. The Tram and Railway share a boundary fence. There is not enough clearance between the Network Rail running lines and the Tram to have a fence so the OHLE Stansions may well require the Tram or the Network Rail Track to be slewed or Headspan holding both AC and DC OHLE equipment.

 

[snowball]

The one area which may be a little difficult may be the quarter of a mile from the Jewellert Quarter towards the Hawthorns. The Tram and Railway share a boundary fence. There is not enough clearance between the Network Rail running lines and the Tram to have a fence so the OHLE Stansions may well require the Tram or the Network Rail Track to be slewed or Headspan holding both AC and DC OHLE equipment.

Going out of Manchester Victoria north-eastwards there is not really a proper fence between Network Rail and Metrolink, just a temporary-looking scaffolding fence for part of the distance. About seven of the OLE gantries span both sets of tracks in a single span (but do not contribute to holding up the Metrolink wires).

 

[Bald Rick]

The one area which may be a little difficult may be the quarter of a mile from the Jewellert Quarter towards the Hawthorns. The Tram and Railway share a boundary fence. There is not enough clearance between the Network Rail running lines and the Tram to have a fence so the OHLE Stansions may well require the Tram or the Network Rail Track to be slewed or Headspan holding both AC and DC OHLE equipment.

Or a twin track cantilever on one side…