East London electrification

[Taunton]

Can anyone please answer some questions on the GE and LTS electrification.

When the 25 Kv system was introduced in the early 1960s, there were several sections where there was insufficient clearance for this, mainly at the inner London ends of the system, and they were electrified at quarter voltage, 6.25 kv. The emus were fitted with automatic changeover equipment, operated magnetically like AWS, but I believe the magnets were mounted just outside the rails rather than between them. Apparently both the GE and the LTS had this arrangement. What were the actual sections this was done on? When were they finally changed over to the standard 25 kv (I think some time in the 1980s)? I seem to recall reading that the entire Chingford line was at 6.25 kv.

I once heard that the same approach was taken on the Glasgow North/South Clyde lines, is there any documentation of which sections these were?

The West Coast main line electrification of the same period nearly got the same arrangement where clearances were tight, but there was some redesign and it was not done.

Would also be interested in detail of the changeover to this system from the old 1500v DC electrification out of Liverpool Street. The trains were converted from DC to AC in what must have been quite an extended programme, but the electrification itself must have been changed from one voltage to another over a weekend. When did this happen? Is it correct that it was about 1961, and the trains for the LTS line were built early and all used on the GE line from changeover date until the conversions were done? The first 20 or so LTS units were never moved on, and operated out of Liverpool Street for most of their lives.

Thank you anyone with information.

 

[D365]

A rather detailed section on the GE/LTS electrification system and the changeover of the former from 1500V DC to 6.25kV AC (with conversion of the original Shenfield suburban units) features in the book 'Eastern Electric' by John Glover.

 

[edwin_m]

The magnets on the ends of the sleepers are still used on 25kV, known as APC magnets (Automatic Power Control I think). One pair is fitted just before and just after a neutral section, with each pair comprising a magnet on each side opposite each other.

The train has a magnetic field sensor mounted on the bogie underneath the pantograph. When it detects a magnet it opens the main circuit breaker, thus ensuring that no current is being drawn when passing into the neutral section. This reduces the risk of an electrical arc that could damage the equipment. On reaching the second magnet the circuit breaker is closed again.

The system worked exactly the same at the voltage changes between 25kV and 6.25kV, but the trains also had a voltage sensor circuit which would detect which voltage was present on passing the second magnet, and configure the transformer windings for 6.25kV or 25kV before the main circuit breaker was re-closed.

Sorry I can't help on the location of the different AC voltages or the DC-AC changeover, though I do know the units built for DC retained their DC control gear, with a transformer and rectifier were added to supply it with 1500V DC from the 25kV AC supply.

 

[red circle]

Go to the 'Railways Archive' and enter emu failures into the search box,you want the 1962 full report into electric train failures on Scottish and eastern regions.Lists the changeover locations and has circuit diagrams etc.

 

[Crisso]

I've never understood why they didn't just leave the Great Eastern as a D.C. area? As well as the intensive Southend (Victoria) route, it was also already electrified out as far as Chelmsford, with all of the D.C. infrastructure, substations, etc., fairly recently in place, being only 4 years old then at best. That would have immediately solved the clearance problems with the North East London ( "Chenford") Electrification. The mileages involved aren't and weren't astronomoic, even including the L.T. & S. Ok, so with subsequent technology in the 1980's, perhaps the line from Colchester to Norwich and Bishops Stortford to Cambridge/Kings Lynn could have been at 25Kv A.C., plus a changeover point for the North London Line at Stratford. Dual voltage Locos/Emus would work seamlessly at the aforesaid necessary changeover points.

Let's be frank (no pun intended...), the French haven't converted large mileages of their former D.C. network?

Feel free to discuss...

 

[Taunton]

Red Circle, thank you very much for that, it gives everything, and a lot more than my initial question. I was aware of the initial failures, and the resulting Ministry report, but had not realised that it was the 6.25/25 Kv changeover equipment itself that was at the heart of the problems, where simplistically this equipment repeatedly malfunctioned, connected the higher voltage to the lower voltage equipment on the train, and blew it up - if you think 'blew it up' is a bit over the top, the report is full of detail of 'explosions'.

The 6.25 Kv was even more extensive than I thought, the whole of the Southend Victoria main line, plus all the NE London inner suburban lines as far out as Cheshunt, used this. The second class only inner suburban stock must hardly have ever run on 25 Kv.

I've never understood why they didn't just leave the Great Eastern as a D.C. area? ------ Dual voltage Locos/Emus would work seamlessly at the aforesaid necessary changeover points....

Gerry Fiennes, in his book 'I tried to run a railway' said exactly the same thing. And he of all people should have known, he was the General Manager of the GE at the time. Of course, the trains were indeed dual voltage, and if you read the accident report linked above you will find all the detail of the problems associated with that, and that 'Seamless' was not a word to use about the changeover points .......

What comes over repeatedly is that at all levels, from the railway management to the Ministry, and indeed the accident investigator himself, everyone thought that they were doing a Good Thing by providing facilities (all at public expense) for multiple UK electrical engineering firms to do what was effectively their development work on BR for any future overseas orders.

 

[Crisso]

Thanks 'Taunton' - and to further clarify what I meant re dual-voltage - not from 6.25kv upto 25kv ac but, actually from 1500 v dc to 25kv ac and vice versa. By the early 1980's this technology with dual ac/dc locos/emus, had been perfected in France and elsewhere, when further substantial extensions within East Anglia were eventually implemented.

Incidentally, I recently travelled from Paris to Mulhouse and whilst a substantial mileage was on the LGV South East plus the LGV Rhone-Rhine - however, from Aisy (near Montbard) via Blaisy Bas summit to beyond Dijon, was on the 1950-52 built 1500 v dc system which seems to work fine and justifies my original argument.

 

[Taunton]

Yes, dual voltage has been successfully cracked nowadays, particularly it seems by the French. The first few miles of your TGV trip out of Gare de Lyon in Paris was on 1,500v dc as well, and the Paris RER is about 50-50 of each, with mid-route changeovers in the centre of Paris. Power electronics, however, are way more advanced nowadays than they were more than 50 years ago.

 

[edwin_m]

A low voltage DC plus a single high voltage AC is reasonably straightforward without using any traction electronics apart from diodes - you just put a transformer and rectifier on the front end of a DC drive and bypass it in DC mode as with the 313 unit. Two voltages at 50Hz is a bit more tricky as it involves switching the windings on the transformer but still achievable in the 60s, well give or take the occasional explosion...

25kV plus 15kV is more difficult since the frequencies are also different so you either need two transformers or a single one that is capable of working at either frequency.