Catenary between Chelmsford and Hatfield Peverel

[Titan]

It's OLE, not OHLE. Overhead is one word.

 

And the GW series 1 is not over engineered. It might be over specified for the short term, but that's a very different thing.

 

Various terminology is used, you can add OCS to those two, any one of them can be considered correct depending on who is writing the document, whether there is an R in the month or whatever...

[Titan]

Hi Ian

 

I have just spent an hour skim reading a 500 page paper from the 1960 OLE conference hoping to find the paragraph that states the 1500V Dc insulators were suitable for 6.25 Kv Ac as I had mentioned on Brian's Southend stock thread. When I do I will send you a copy.

 

I have started reading and have not found it yet either, however it does state that the same 4 inch air gap for 1500VDC is also suitable for 6.25kV when it comes to bridge clearances.

[rodent279]

It's OLE, not OHLE. Overhead is one word.

 

And the GW series 1 is not over engineered. It might be over specified for the short term, but that's a very different thing.

I like the GW OLE. It's growing on me.

[Zomboid]

Various terminology is used, you can add OCS to those two, any one of them can be considered correct depending on who is writing the document, whether there is an R in the month or whatever...

OCS (to me) only describes part of the system. If there are Return Conductors, ATFs or Aerial Earth Wires then none of those would count as part of the contact system.

But I'm not the oracle on these things, I just get a bee in my bonnet over GW being called "over engineered" by people who don't have the knowledge to say that, and OHLE bothers me, too...

[rodent279]

My dad worked in electrification, her did the Roade-Euston section of the WCML. He always referred to it as overhead line or OLE. Sometimes he'd say catenary, but that, as I understand it, strictly refers to the curved wire that supports the contact wire, which is supposed to describe a catenary curve.

Having flashbacks of evening classes at college now, trying to get my head around hyperbolic differentiation. Sinh,cosh,tanh etc. Happy days!

Edited January 3, 2018 by rodent279

[keefer]

the official report into the EMU transformer explosions in the early '60s is a good source of info regarding the 1500V/6.25kV/25kV changeover.

 

http://www.railwaysarchive.co.uk/documents/MoT_EMUFailures1962.pdf

 

There's a lot of detail into how the systems came about, what was used where and also details of the trains etc. (you could lose yourself in this for a while)

 

Regarding clearances etc., on p.6 (p.11 of PDF):

" 23. The equipment is the same for 25 kV and 6.25 kV except that smaller insulators are used for the lower voltage; on the Liverpool Street-Shenfield-Southend-Chelmsford converted lines most of the original 1,500 volts D.C. equipment has been retained. The normal height of the contact wire is 16 ft. above rail level but under low tunnels and bridges where the loading gauge is 13 ft. 1 in. it is reduced to 14 ft. on the 25 kV lines and 13 ft. 5 in. on the 6.25 kV lines; at public level crossings it is increased to 18 ft. 6 in. for 25 kV and 18 ft. for 6.25 kV."

 

States that the min clearance for 6.25kV was 4", but doesn't specifically say the same insulators were used - only that 'most of the original 1500V DC' equipment was used.

 

also on p.9 (p.14 of PDF):

" 42. [Liv. St. - Shenfield - Southend] It was considered that the clearances already provided for 1,500 volts would be suitable for 6.25 kV A.C., and consequently the major part of the system (all except the Shenfield-Chelmsford line) was converted to this voltage."

[rodent279]

My dad says they did tests with two steam locos belching out steam and smoke side by side, and found there was no flashover until well under 4".

[Clive Mortimore]

the official report into the EMU transformer explosions in the early '60s is a good source of info regarding the 1500V/6.25kV/25kV changeover.

 

http://www.railwaysarchive.co.uk/documents/MoT_EMUFailures1962.pdf

 

There's a lot of detail into how the systems came about, what was used where and also details of the trains etc. (you could lose yourself in this for a while)

 

Regarding clearances etc., on p.6 (p.11 of PDF):

" 23. The equipment is the same for 25 kV and 6.25 kV except that smaller insulators are used for the lower voltage; on the Liverpool Street-Shenfield-Southend-Chelmsford converted lines most of the original 1,500 volts D.C. equipment has been retained. The normal height of the contact wire is 16 ft. above rail level but under low tunnels and bridges where the loading gauge is 13 ft. 1 in. it is reduced to 14 ft. on the 25 kV lines and 13 ft. 5 in. on the 6.25 kV lines; at public level crossings it is increased to 18 ft. 6 in. for 25 kV and 18 ft. for 6.25 kV."

 

States that the min clearance for 6.25kV was 4", but doesn't specifically say the same insulators were used - only that 'most of the original 1500V DC' equipment was used.

 

also on p.9 (p.14 of PDF):

" 42. [Liv. St. - Shenfield - Southend] It was considered that the clearances already provided for 1,500 volts would be suitable for 6.25 kV A.C., and consequently the major part of the system (all except the Shenfield-Chelmsford line) was converted to this voltage."

Thanks Keefer

 

As for the insulators, photos would suggest the 1500V Dc were not taken down until each section was converted to 25 Kv Ac.

[gobbler]

Well it seems this topic has piqued certain interests.

 

I didn't think for one moment I'd get half the information and pictures/diagrams that have been freely forthcoming.

 

Thanks to everyone that had joined in.

 

Cheers

 

Scott

[DY444]

My dad says they did tests with two steam locos belching out steam and smoke side by side, and found there was no flashover until well under 4".

 

At Crewe iirc

[The Stationmaster]

My dad says they did tests with two steam locos belching out steam and smoke side by side, and found there was no flashover until well under 4".

 

They also tested for flashover on insulators which had become quoted in smoke and soot from steam engines - I got the impression from an article at the time that carbon build up on insulators was a very big concern.  In fact on some sections of the LM electrification the insulators were wrapped in what looked like plastic sheet and weren't uncovered until just before a section went live - again presumably because of concern about carbon build up.

[cheesysmith]

Its strange to think that BR had got clearances down for 25Kv to 150mm, or 100mm in limited clearance places. Thats 6in or 4in in old money, same as what is quoted above for 6.25Kv. As for the use of the old DC bits with higher voltage AC power, remember that the old equipment was very conservatively rated, and the DC bits could actually have a voltage a lot higher than 1500v, especially the Woodhead when you had locos in regen mode downhill. There is even a picture in one of the books of the EM1s (cant find it at the mo) of a EM1 under test whilst being constructed with a safety barrier and the wording warning of 5000v (IIRC).

[rodent279]

Its strange to think that BR had got clearances down for 25Kv to 150mm, or 100mm in limited clearance places. Thats 6in or 4in in old money, same as what is quoted above for 6.25Kv. As for the use of the old DC bits with higher voltage AC power, remember that the old equipment was very conservatively rated, and the DC bits could actually have a voltage a lot higher than 1500v, especially the Woodhead when you had locos in regen mode downhill. There is even a picture in one of the books of the EM1s (cant find it at the mo) of a EM1 under test whilst being constructed with a safety barrier and the wording warning of 5000v (IIRC).

1500V D.C. insulators would have to be rated for the highest voltage that could reasonably be expected in service, given variations in supply from the grid, and whether there was enough load to absorb power generated by locos in regen mode.

 

I believe that the substations had thyratrons installed which switched in load resistances when the line voltage exceeded a certain value-1900V rings a bell, but don't quote me on that.

 

Given that 6.25kV is the R.M.S. voltage, the peak voltage will be around 8.75kV, 100 times a second. I would be surprised if insulators rated at 1.5kV D.C. would be reliable when exposed to that sort of voltage, day in day out, in all weathers.

Edited January 4, 2018 by rodent279

[Clive Mortimore]

1500V D.C. insulators would have to be rated for the highest voltage that could reasonably be expected in service, given variations in supply from the grid, and whether there was enough load to absorb power generated by locos in regen mode.

 

I believe that the substations had thyratrons installed which switched in load resistances when the line voltage exceeded a certain value-1900V rings a bell, but don't quote me on that.

 

Given that 6.25kV is the R.M.S. voltage, the peak voltage will be around 8.75kV, 100 times a second. I would be surprised if insulators rated at 1.5kV D.C. would be reliable when exposed to that sort of voltage, day in day out, in all weathers.

Hi

 

Hopefully these photos will show that the 1500 v DC gear continued to be used up until conversion to 25 Kv AC in the 80s.

 

I have chosen some photos taken roughly the same spot at Stratford.

 

A Britannia in the 1950s, running under 1500 V DC.

 

A BTH in the 1960s after conversion to 6.25Kv AC

 

A Class 31 and 37 in the 1970s with the same type of insulators.

 

A Clacton unit in the 1980s after conversion to 25 Kv AC, not only note the change of insulators but 615 is running as a 3 car unit following the removal of the BUFFET.

 

A pair of 37s in the 1990s only because I like triple grey livery.

 

A more recent class 90, the mast haven't changed the track and platforms under them have.

 

And to finish off, just a nice photo of a J15.

 

I hope you enjoy the journey through time at Stratford, and not one class 47 with a silver roof.

[rodent279]

Well there you go, I stands corrected! That does surprise me but you live & learn.

 

I suppose the 1500V D.C. insulators, being designed in the steam era, may have been over engineered to take into account steam, soot & grime deposits.

 

I'll take a grey or silver roofed 47 any time!

Edited January 5, 2018 by rodent279