Electrification Voltage Upgrades and Bi Modes

[Aictos]

As per subject title, how much work and what exactly needs to be done to upgrade from a 1.5kV DC OHL system to the UK standard 25kV AC OHL System?

The reason I was wondering about this is simply because in the Dublin area, Iarnród Éireann who operate the Dublin Area Rapid Transit system has plans to electrify the Western Commuter line from Dublin Connolly to Maynooth as a extension of the network.

However I believe they have already stated that future electrification on the Irish network is planned to be at 25kV AC power, while the existing DART network will remain at 1.5kV DC.

Which brings me to Bi Modes, is it cheaper to electrify at 25kV AC power including DART Metals, keep the existing DART network at 1.5kV DC and use Bi Modes which can work off either system OR
electrify the Irish Network at 25kV AC power and upgrade the existing DART network to use this instead of the existing 1.5kV DC?

 

[Mollman]

I think you mean duel voltage rather than bi-mode. BR did change the voltage on the Great Eastern mainline and surviving part of the Woodhead route from 1.5kv DC to 25kv AC so it is practical but may involve changes to feed locations and substations.

 

[DPWH]

I don't think he meant duel voltage unless drivers have to fight each other with cattle prods?

 

[Joseph_Locke]

I think you mean duel voltage rather than bi-mode. BR did change the voltage on the Great Eastern mainline and surviving part of the Woodhead route from 1.5kv DC to 25kv AC so it is practical but may involve changes to feed locations and substations.

... and OLE to structure clearances, bridge parapet heights, insulator ratings, fault current settings, section insulators, earthing and bonding of lineside structures, wire heights at stations, EMC screening for telecoms kit, immunisation of signalling equipment, safety signage, lineside fencing, level crossing risk reassessments ...

 

[Aictos]

... and OLE to structure clearances, bridge parapet heights, insulator ratings, fault current settings, section insulators, earthing and bonding of lineside structures, wire heights at stations, EMC screening for telecoms kit, immunisation of signalling equipment, safety signage, lineside fencing, level crossing risk reassessments ...

Which of course can add up to a lot of money but in the long run is it really economical to have two separate systems especially with the added costs that trains which can use either system will cost compared to trains that just use one system?

 

[AM9]

As per subject title, how much work and what exactly needs to be done to upgrade from a 1.5kV DC OHL system to the UK standard 25kV AC OHL System?

The reason I was wondering about this is simply because in the Dublin area, Iarnród Éireann who operate the Dublin Area Rapid Transit system has plans to electrify the Western Commuter line from Dublin Connolly to Maynooth as a extension of the network.

However I believe they have already stated that future electrification on the Irish network is planned to be at 25kV AC power, while the existing DART network will remain at 1.5kV DC.

Which brings me to Bi Modes, is it cheaper to electrify at 25kV AC power including DART Metals, keep the existing DART network at 1.5kV DC and use Bi Modes which can work off either system OR
electrify the Irish Network at 25kV AC power and upgrade the existing DART network to use this instead of the existing 1.5kV DC?

It depends on a few things that you haven't mentioned:

how far the route is already electrified at 1500VDC
how intensive a service is run over that section compared with the ac extension
how much further beyond Maynooth they might consider a candidate for electrification in the future​

Dual voltage OLE trains are perfectly do-able as the many lines using it in continental Europe testify. It would probably need dual pantographs but the design options for 750VDC 3rd rail/25kV ac ole powered trains are quite established. The existing DC-only trains could then continue to run normally to the limits of the DC wiring. When they are life-expired, their replacement stock could then be dual voltage allowing a progressive changeover to ac.
There would be the need to do as Joseph Locke says when DC lines were converted, and the structural clearances would need to be addressed on the currently unelectrified section.

 

[swt_passenger]

Which of course can add up to a lot of money but in the long run is it really economical to have two separate systems especially with the added costs that trains which can use either system will cost compared to trains that just use one system?

There’s very little extra onboard technology needed to be able run on either voltage. The nature of modern units is that they usually have a ‘DC link’ stage somewhere between the pantograph/transformer and the traction converter. Even if it’s within a big black box. Units that can run on either AC or third rail DC are commonplace and the only real difference is the addition of shoe-gear and associated cabling, a fairly trivial amount of equipment in terms of the overall cost.

 

[hwl]

As per subject title, how much work and what exactly needs to be done to upgrade from a 1.5kV DC OHL system to the UK standard 25kV AC OHL System?

The reason I was wondering about this is simply because in the Dublin area, Iarnród Éireann who operate the Dublin Area Rapid Transit system has plans to electrify the Western Commuter line from Dublin Connolly to Maynooth as a extension of the network.

However I believe they have already stated that future electrification on the Irish network is planned to be at 25kV AC power, while the existing DART network will remain at 1.5kV DC.

Which brings me to Bi Modes, is it cheaper to electrify at 25kV AC power including DART Metals, keep the existing DART network at 1.5kV DC and use Bi Modes which can work off either system OR
electrify the Irish Network at 25kV AC power and upgrade the existing DART network to use this instead of the existing 1.5kV DC?

Plenty of dual voltage/frequency EMUs in France Belgium Netherlands Austria Czech Rep, Slovenia, Ukraine as SWT passenger has said very trivial these days to implement.

 

[hooverboy]

are you talking about line equipment or loco's?

loco's is a fairly straightforward conversion, just a box with an inverter in and a few mods to control systems

line equipment_ read joseph lockes posts. he's pretty much nailed it...aside from voltage conversion(the simple bit) there's also EMC,elf+safety and equipment capability to consider.

ie a wire carrying 1500v dc will have a different gauge than 25kvAC...to get the correct impedance for that length of line,not to dissipate too much power in the cables themselves.
...which in turn needs different insulators(breakdown voltages),neutral sections, arcing considerations,wire tensioning etc etc

 

[edwin_m]

The new equipment could be designed to be compatible with both voltages (clearances and insulators etc suitable for 25kV, possibly a thicker gauge wire to allow 1500V in the meantime - or maybe that part wouldn't be necessary if it was just a smallish area around Connolly).

 

[Aictos]

It depends on a few things that you haven't mentioned:

how far the route is already electrified at 1500VDC
how intensive a service is run over that section compared with the ac extension
how much further beyond Maynooth they might consider a candidate for electrification in the future​

Dual voltage OLE trains are perfectly do-able as the many lines using it in continental Europe testify. It would probably need dual pantographs but the design options for 750VDC 3rd rail/25kV ac ole powered trains are quite established. The existing DC-only trains could then continue to run normally to the limits of the DC wiring. When they are life-expired, their replacement stock could then be dual voltage allowing a progressive changeover to ac.
There would be the need to do as Joseph Locke says when DC lines were converted, and the structural clearances would need to be addressed on the currently unelectrified section.

Actually I have said how far the route is already electrified at 1500VDC - as I did say the existing DART network was planned to keep this system.

I just wondered why keep this system when while you're electrifying the Dublin Suburban lines and then the lines to Cork and Belfast why not just use 25kV AC instead.

 

[AM9]

Actually I have said how far the route is already electrified at 1500VDC - as I did say the existing DART network was planned to keep this system.

I just wondered why keep this system when while you're electrifying the Dublin Suburban lines and then the lines to Cork and Belfast why not just use 25kV AC instead.

Because it would mean all DART trains needed to be replaced/modified plus the OLE specification changed in respect of the characteristics/features that Joeseph Locke described above. 25kV ac is certainly beneficial on the outer suburban line to Maynooth, but unless wholsale replacement is actually needed on the DC system, with the frequent stops and short distances run, there is not really a case for replacing kit that was installed new in the early 'eighties.

 

[Bald Rick]

Which of course can add up to a lot of money but in the long run is it really economical to have two separate systems especially with the added costs that trains which can use either system will cost compared to trains that just use one system?

The paragon of virtue that is SNCF seems to think so. Almost every TGV ever built has 25kV AC and 1.5kV D.C. capability

 

[snowball]

The tram/train extension to the Sheffield Supertram system, about to enter service, is 750 V DC overhead, designed for possible future conversion to 25 kV AC, and has been delayed by a couple of years, with large cost increases, because Network Rail developed a whole new set of designs for it. The vehicles are dual-current.

 

[jh64]

That also seems to be in the spec for the new Tyne and Wear Metros, keeping the DC lines for the Metro only route and switching to AC when joining the main line. That would enable rewiring the stretch from Newcastle to Sunderland to AC in the future.

 

[edwin_m]

That also seems to be in the spec for the new Tyne and Wear Metros, keeping the DC lines for the Metro only route and switching to AC when joining the main line. That would enable rewiring the stretch from Newcastle to Sunderland to AC in the future.

I seem to recall the Sunderland line was also wired with 25kV-compatible equipment at the time, though given the changes in standards I guess much of it might have to be replaced should they ever consider converting it.

 

[AndrewE]

Wasn't most of the original MSW line 1500V OLE kept in use when the Hadfield / Glossop lines were converted to 25kV AC?

 

[AM9]

Wasn't most of the original MSW line 1500V OLE kept in use when the Hadfield / Glossop lines were converted to 25kV AC?

I can't speak about the Manchester lines but the original GE OLE was unchanged (other than the feeds) when from Liverpool St to Harold Wood was converted to 6.25kV and mostly only the insulators were changed when the voltage was lifted to 25kV. Some of the original fixed-tension compound catenary wasn't changed until the early 2000's and to this day many of the original 'A' framed gantries are still holding the knitting up!

 

[snowball]

Wasn't most of the original MSW line 1500V OLE kept in use when the Hadfield / Glossop lines were converted to 25kV AC?

And Manchester to Altrincham too?

 

[AndrewE]

And Manchester to Altrincham too?

I guess they must have just changed the voltage, as Wikipedia says they withdrew the 1500V DC trains running (at that stage) between Altrincham and Oxford Rd on 30 April and restarted with 25kV AC on 3rd May 1971.

 

[racyrich]

How does the train switch from one to the other? I can see how 3rd rail dc and OHLE ac can be kept electrically separate in the train, but 2 OHLE systems which presumably the pantograph is going to connect - how does that work?

 

[daveshah]

How does the train switch from one to the other? I can see how 3rd rail dc and OHLE ac can be kept electrically separate in the train, but 2 OHLE systems which presumably the pantograph is going to connect - how does that work?

Particularly as 25kV AC going into 1500V DC system; and 1500V DC going into a transformer are both likely to be pretty catastrophic...

 

[swt_passenger]

How does the train switch from one to the other? I can see how 3rd rail dc and OHLE ac can be kept electrically separate in the train, but 2 OHLE systems which presumably the pantograph is going to connect - how does that work?

Maybe two overlapping catenary lengths, separately switched, with only one live at a time? There’ll be a solution already in use somewhere, whatever it happens to be...

 

[Pigeon]

Easy... You have a neutral section between the two to make sure the pantograph does not connect them, just as you already have between different sections of 25kV overhead. And you have control equipment such that when the pantograph comes off the neutral section and goes live again, that alone does not re-establish a feed to the power conversion equipment; instead the control equipment determines what kind of feed the pantograph is getting and activates contactors to feed it to the appropriate input.

This is pretty much what used to be done to enable switching between 6.25kV and 25kV on the fly. It used to thump-bang a bit, but it's easier to control these days.

 

[Bald Rick]

I can't speak about the Manchester lines but the original GE OLE was unchanged (other than the feeds) when from Liverpool St to Harold Wood was converted to 6.25kV and mostly only the insulators were changed when the voltage was lifted to 25kV. Some of the original fixed-tension compound catenary wasn't changed until the early 2000's and to this day many of the original 'A' framed gantries are still holding the knitting up!

Most of the GE FT catenary has only gone in the last 6 years or so, indeed there is still some up (with original contact wire) around Stratford.

 

[AM9]

Easy... You have a neutral section between the two to make sure the pantograph does not connect them, just as you already have between different sections of 25kV overhead. And you have control equipment such that when the pantograph comes off the neutral section and goes live again, that alone does not re-establish a feed to the power conversion equipment; instead the control equipment determines what kind of feed the pantograph is getting and activates contactors to feed it to the appropriate input.

This is pretty much what used to be done to enable switching between 6.25kV and 25kV on the fly. It used to thump-bang a bit, but it's easier to control these days.

Standard ac/DC OLE practice in mainland Europe is to have separate pantographs for each system. Changeover usually happens on the move when the first system pantograph lowers, the train then coasts through a neutral section, then the second system pantograph rises. Track balises signal to the loco/EMU when to raise/lower pantographs. Thus there is less chance for the wrong supply to be fed into the switchgear.
As an aside, as getting traction motors to work with voltages much above 750V difficult, it was normal for 1500VDC vehicles to feed pairs of motors in series. That gives a benefit in the resistors used for speed control at the expense of more complicated switchgear. The trick was to wire both motors in a bogie in series and both bogies in series. Then at starting, the series resistors are switched out as the speed increases. When all of the resistors are switched out, a changeover circuit breaker switches each bogie pair to the 1500V feed via resistors. As the speed increases more those resistors are switched out until the motors each are running on 750V bu virtue of them being one of two in a series connection. Those who remember the class 306 EMUs on the GEML might remember the loud knocking (sometimes repeatedly) as the changeover circuit breaker kicks in.

 

[AM9]

Most of the GE FT catenary has only gone in the last 6 years or so, indeed there is still some up (with original contact wire) around Stratford.

Who says that electrification isn't a sound investment!

 

[fat_boy_pete]

I can't speak about the Manchester lines but the original GE OLE was unchanged (other than the feeds) when from Liverpool St to Harold Wood was converted to 6.25kV and mostly only the insulators were changed when the voltage was lifted to 25kV. Some of the original fixed-tension compound catenary wasn't changed until the early 2000's and to this day many of the original 'A' framed gantries are still holding the knitting up!

Actually, last bit will only be replaced this Christmas!
They still have another year or so to go to replace the 60 year old fixed tension catenary on the Southend Victoria line.

 

[edwin_m]

Easy... You have a neutral section between the two to make sure the pantograph does not connect them, just as you already have between different sections of 25kV overhead. And you have control equipment such that when the pantograph comes off the neutral section and goes live again, that alone does not re-establish a feed to the power conversion equipment; instead the control equipment determines what kind of feed the pantograph is getting and activates contactors to feed it to the appropriate input.

This is pretty much what used to be done to enable switching between 6.25kV and 25kV on the fly. It used to thump-bang a bit, but it's easier to control these days.

It used to explode from time to time on the Glasgow blue trains in the early years, but they sorted that out.

The Sheffield and other tram-trains use a similar system*. I think it has to be a longer neutral section than usual so the traction equipment has time to realise and disconnect itself, otherwise it would just assume that a short break in the supply meant no change of voltage.

*Or at least the Sheffield ones would if the main line was energised at 25kV. It's all 750V currently but if 25kV was ever needed the vehicle has the relevant equipment and the catenary is easily convertable including installing the changeover section.

Standard ac/DC OLE practice in mainland Europe is to have separate pantographs for each system. Changeover usually happens on the move when the first system pantograph lowers, the train then coasts through a neutral section, then the second system pantograph rises. Track balises signal to the loco/EMU when to raise/lower pantographs. Thus there is less chance for the wrong supply to be fed into the switchgear.

Certainly the case for many trains, but as above the tram-train can get away with a single pantograph possibly because it's slower so dynamic issues are less critical. Multiple pantographs may be about matching the different dyanmics of different OLE systems as much as the fact the voltage was different. There must be a means to raise them manually, hence automatic voltage detection on a single pantograph avoids the risk of damage if the driver raises the wrong one.

 

[grumpyoldman01]

Particularly as 25kV AC going into 1500V DC system; and 1500V DC going into a transformer are both likely to be pretty catastrophic...

There were some problems around Nice in about 1990 which I was told by a senior SNCF traction engineer illustrated the consequences of the first example.

The line is electrified at 25kv AC, but as it is DC around Marseilles, trains were worked at that time by dual voltage locos; the overhead was energized in such a way that a train drawing power on one line could significantly reduce the voltage on another, and a TGV set starting from the station could reduce the line voltage elsewhere so that a loco could think it was only getting 1500v. Therefore, (as I understand it, not being a traction engineer) the dual voltage loco set for AC automatically changed to its DC settings (based upon a voltage reading), and that was OK for as long as the TGV was drawing power in the same section; however, as soon as the TGV passed into another one, the automatic voltage selector on the dual voltage loco was unable to react quickly enough to the sudden surge in voltage and change back to high voltage AC settings - and it caught fire! I was told this had happened more than once.

I don't know what the long term solution was, but - if I remember correctly - the short term one was to ensure no other locos in the same section had their pantographs raised when a TGV departed!