Maximum Voltage for Street Running

[HSTEd]

Well I'm not sure if this is really metro or infrastructure so I will just post it here.

Ive always thought that 750V was the maximum feasible voltage for electrified railways running on public streets for various discharge reasons. (double decker bus or artic runs under the wires and causes a discharge = big court case)
However I have just discovered that one of the last surviving remnants of the "Interurbans" (South Shore Line) appears to run down public streets using overhead equipment rated for 1500V.

Is this a result of the equipment in America being higher above the road surface or is it just a historical easement to acceptable practice?

 

[DaveNewcastle]

I'm not exactly claear what your question is here, the word 'feasable' seems to be at the heart of it.

We have many level crossings over 25kV electrified lines in the UK. In rural Northumberland there are many level crossings and in the harvest season some huge harvesters cross the ECML without an isolation. (As you probably know, the OHLE conductor rises by approx. 2 meters on either side of these crossings to provide more clearance).

From an electrical point of view, I can't see there's much difference between an on-street overhead and a crossing over a railway. From the point of view of a Risk Assessment however, its hard to see how any new proposal for a high voltage system in close proximity to uncontrolled road vehicles and pedestrians would be assessed as low-risk.

 

[HSTEd]

Indeed we do, but what I will attempt to clarify my question:

If a new street tramway/interurban railway was to be constructed in the UK, what would be the highest voltage that it would be permitted to use for its traction supply? 750V or would higher voltages such as the 1500V used on the South Shore line be acceptable?

 

[krus_aragon]

Speaking purely from memory, a recent NR(?) survey on how to electrify quiet branch lines in the future mentioned (I think) 10kV overhead, in a quasi-tramlike manner.

The 1500V overhead AC was first popularised in the UK, when some government committee declared that all third rail should be 750V DC, and all overhead 1500V AC, for compatability between lines. (This was before the days of 25kV.) 1500V was known in some parts of the world as the 'British System' at one point.

The main reason for the 750V 'limit' is that's all the DC you can pump through a rail before you lose so much current that you need a power station at every lamppost to compensate.

 

[33056]

Not in the UK but this section is 11kv AC......

 

[stanley T]

Speaking purely from memory, a recent NR(?) survey on how to electrify quiet branch lines in the future mentioned (I think) 10kV overhead, in a quasi-tramlike manner.

The 1500V overhead AC was first popularised in the UK, when some government committee declared that all third rail should be 750V DC, and all overhead 1500V AC, for compatability between lines. (This was before the days of 25kV.) 1500V was known in some parts of the world as the 'British System' at one point.

The main reason for the 750V 'limit' is that's all the DC you can pump through a rail before you lose so much current that you need a power station at every lamppost to compensate.

Actually, on the good old power = amps x voltage, at higher voltages you need less current. Manchester-Bury was 1200V DC third rail for many years, the Hamburg S bahn still is, and the Culoz-Modane line in France was 1500 V DC third rail for many years, as are two of the lines on the Guangzhou metro.
Discussed in this thread.

Above 1500V third rail, too much risk of arcing and leaking current. All these are/were heavy rail, bottom or side contact, would be hairy for street running. 750V DC overhead seems to be the norm for trams, which need little power and at that voltage clearances are low.

A committee in 1920 in the UK recommended 1.5kV DC, but little was done until the decision to go to 25kV AC in 1955. Conversely there was extensive electrification on that standard in France, the Netherlands, and Japan.

 

[HSTEd]

So 10kV is apparently reasonable for street running? Because now I'm imagining some sort of monstrous tram with 10kV autotransformer fitted overhead equipment.......


That would be awesome

 

[apk55]

Normal road vehicles can be up to 4.3M high according to legislation. Road over bridges normally have to be at least 4.8M above the road to allow for safety margin and suspension bounce etc, otherwise warning signs need fitting. I presume this applies to overhead wires which will also need some additional hight for electrical clearance, so they would need to be at least 5M above road surface.

 

[jopsuk]

If you were building a new tramway from scratch, you'd most likely go for a 750V DC system, primarily because it means you can use off-the-shelf components, all the tram suppliers already build 750V trams giving you choice etc. Similar to one of the big reasons you'd go for 25kV for a new mainline OHL system in most cases.

 

[HSTEd]

I was pondering some sort of hybrid system like the Tyne and Wear Metro with added street running, where the highest possible voltage that could be used continiously across teh entire line would be beneficial for the same reasons 25kV beats 1.5kV DC.

 

[merlodlliw]

Out of interest, what voltage would the old Colwyn Bay to Llandudno, or the Rhos W/X to Wrexham have used, or indeed today's Blackpool trams.

Bob

 

[jopsuk]

I was pondering some sort of hybrid system like the Tyne and Wear Metro with added street running, where the highest possible voltage that could be used continiously across teh entire line would be beneficial for the same reasons 25kV beats 1.5kV DC.

With modern insulators, is there any (non fincancial) reason why the T&W system couldn't be converted to 25kV?

 

[142094]

With modern insulators, is there any (non fincancial) reason why the T&W system couldn't be converted to 25kV?

Converting the exisiting stock would no doubt be the biggest problem, and then you'd need to upgrade the power supply.

You would probably be able to do it if new stock was introduced but at the same time it is weighing up the cost of conversion with what the money could be spent on instead (such as extensions).

 

[krus_aragon]

Out of interest, what voltage would the old Colwyn Bay to Llandudno, or the Rhos W/X to Wrexham have used, or indeed today's Blackpool trams.

Bob

(leaps for his Oakwood Press book...)

The Llandudno & Colwyn Bay Electric Railway ran on 500-550V DC.

 

[boing_uk]

Blackpool was 550v DC and has been increased to 600v.

 

[Freel07]

ORR Guidance recommends 750 volts DC as the maximum and requires special clearance form the Inspectorate for a higher voltage. Traditional tramways were all nominally 500 volts DC. Blackpool was until very recently 550 volts DC and is now 600 volts DC to cope with the new trams.

 

[Nym]

With modern insulators, is there any (non fincancial) reason why the T&W system couldn't be converted to 25kV?

Personally for the T&W System...

If we want to 25KV the heavy rail lines in the area, then what needs to be done is T&W Metro either orders new stock or converts it's existing stock to dual voltage units that can collect from pantograph either 1500VDC or 25KVAC this would reduce the overall number of non-standard units kicking about on the network.

ie. anything with 25KV could run into Sunderland rather than having to have a special type of heavy rail stock that can collect from 1500DC aswell, it would be better to adapt the T&W system for 25KVAC as it reduces, like I said, the number of Non-Standard units.

 

[merlodlliw]

(leaps for his Oakwood Press book...)

The Llandudno & Colwyn Bay Electric Railway ran on 500-550V DC.

many thanks sent you a PM


Bob

 

[142094]

Personally for the T&W System...

If we want to 25KV the heavy rail lines in the area, then what needs to be done is T&W Metro either orders new stock or converts it's existing stock to dual voltage units that can collect from pantograph either 1500VDC or 25KVAC this would reduce the overall number of non-standard units kicking about on the network.

ie. anything with 25KV could run into Sunderland rather than having to have a special type of heavy rail stock that can collect from 1500DC aswell, it would be better to adapt the T&W system for 25KVAC as it reduces, like I said, the number of Non-Standard units.

One of the things the Sunderland extension shows you is that there will be no electrification schemes in this area for a good few years - otherwise Railtrack at the time wouldn't have allowed the Metro to expand. The extension is less than 10 years old, so no way will it be changed. Also, the Metrocars are just about to undergo refurbishment to prolong their life, so again new stock will not be an answer for at least 10 years or so.

 

[ChrisCooper]

Having to fit transformer under the Metro Cars would increase their weight, and also take up space which would probably reduce passenger capacity (especially as new stock would possibly have the likes of aircon taking up even more space). The transformers would only be in use for the short section to Sunderland, and the rest of the time would be dead weight. Fitting modern AC EMUs to run off 1500v though would be pretty easy, and would require no more equipment than fitting them to run off 750v.

 

[142094]

Even if transformers were to be fitted, there isn't the room in the undercarriage anyway - so as you say it would either be other rolling stock to be altered or wait for new stock on the Metro.

 

[HSTEd]

Isnt the metro rolling stock partially derived from the stock they use in Karlsruhe? They seem to have dual voltage vehicles without major disadvantage. And they have transformers that would have to be atleast three times as heavy as ours would due to the low main line electrification frequency.

 

[142094]

Isnt the metro rolling stock partially derived from the stock they use in Karlsruhe? They seem to have dual voltage vehicles without major disadvantage. And they have transformers that would have to be atleast three times as heavy as ours would due to the low main line electrification frequency.

They were designed along the lines of the Stadtbahnwagen B - but retrofitting any new electrical work would be both costly and difficult.

 

[HSTEd]

They were designed along the lines of the Stadtbahnwagen B - but retrofitting any new electrical work would be both costly and difficult.

As it would appear that no further stock was purchased for the Sunderland extension, you could potentially replace the stock on that line early with dual voltage capable stock adn concentrate the remaining original stock on the other line for the remainder of its life, perhaps extending it if the funding is available, without leaving it all obsolete early.

 

[142094]

As it would appear that no further stock was purchased for the Sunderland extension, you could potentially replace the stock on that line early with dual voltage capable stock adn concentrate the remaining original stock on the other line for the remainder of its life, perhaps extending it if the funding is available, without leaving it all obsolete early.

That was mainly due to the fact the service on the Coast line was reduced and the fleet has been used more intensively. Note that stock used on the extension is still used on the rest of the system, so you would have problems if one type needed to be withdrawn for maintenance etc.

In short whilst the idea is feasible, it isn't going to happen.