OHL between Hitchin/Cambridge and Hertford Loop

[Aictos]

I know there were some issues with the OHL on the Cambridge branch as the OHL is poor there but I didn't realise the Hertford loop was just as bad which makes me think that if the Cambridge branch is going to have the OHL upgraded, would they get the Hertford Loop done as well?

Actual wording of the section entitled Dropping Pantographs for unit movements on the basic driver's guide to the Class 317, it states that Some sections of First Capital Connect infrastructure have very poor Overhead line power such as round the Hertford North branch or between Hitchin and Cambridge. If you are required to work a 12 car train over these areas, you may need to ask the fitters and SDC if you need to drop a pan.

Never heard of the Hertford route being as bad as the Cambridge route, I just thought the Cambridge route was bad.

Is there any other areas of FCC routes on both the TL and GN where restrictions apply?

 

[O L Leigh]

I'm not entirely sure that's correct.

There is pictorial evidence of 86101 on a set of empties and of a Cl91 running light through Hertford North, so the power supply must be better there than it is on the Shepreth Branch because the only electric loco cleared to run on that line is a light Cl86. All others are banned. I can also recall no restrictions on the OLE on the Hertford North line pertaining to electric units mentioned in the Sectional Appendix. So quite where FCC get these instructions for the Hertford loop I just couldn't say.

O L Leigh

 

[Lee_Again]

After the accidents at Hatfield and Potters Bar, when the main line was shut, I travelled on the Hertford Loop numerous times with a cl91. I think the signalling gives up on that stretch before the OHL. Mind you, the line speeds are max.90 I think (somebody will know).

It's also often used on Sundays.

Not sure about the Cambridge branch. Of course, there's little point sending a cl91 up there as there's no route back, except with assistance.

 

[Aictos]

Well the line speed is only 75mph for passenger use and it goes from 60mph to about 30 to 40mph at one of the London end stations for freights.

I've seen countless 91s go though the line both with Mk4 sets and light engine, in fact the only restriction I'm aware of is you cannot have more then 24 electrics on the line in any one hour period, although I may need to double check that number but I'm sure I'm right.

As to 90mph running, I wish!

Cheers guys,

 

[MCR247]

Including 313s?

 

[Aictos]

Including 313s?

No, line speed to be raised to 90mph except for 313s which would remain at 75mph and freights of course.
Never going to happen though, is it

But saying that, with investment it could be possible.

 

[philjo]

I believe that the Royston-Cambridge section was electrified on the cheap in 1987 which meant it had limited power available.

NR had to upgrade the power supply on this section before FCC could introduce the 12-car peak-hour services that now run to/from Cambridge as from the may 2009 timetable change.
Don't know if this additional power would be enough to now allow electric locos to use the line though.

 

[Old Timer]

OHL Electrification infrastructure consists of two elements, traction supply and distribution, and the OHL catenary system.

In the case of traction supply, the provision and spacing of the feeder stations is based upon the peak demand. This is determined by the power consumption of the EMU types, the speed of the trains and the number of trains within the section at peak demand.

In the case of the OHL Catenary system, the design reflects the speed of the trains, which in turn sets out the tensioning of the Catenary system as well as the type and positioning of the OHL structures. For the purists, the GN Inner Suburban was the first use of the BR standard Mk3 equipment easily recognised by the headspan cross-track support system.

Looking at the case with the GN, the Inner Suburban section (kings Cross/Moorgate to Royston) was completed between 1974 and 1978.

At the design stage, train speeds were based upon 75mph EMU running, and it was for this speed that the OHL Catenary system was tensioned and the structure spacing specified.

The power demand was based on 2 x 3-car emus

When the electrification was extended to Peterborough in the 1980s, the OHL system was designed on this section for 100 mph running.

The traction supply arrangements at that time did not anticipate anything other than EMUs operating. Peterborough was only reached because a man called Norman Howard who was then the head of Electrification at the BRB made considerable efforts to gain approval for the use of "spare" and over-ordered stock from the Bedford - St Pancras/Moorgate scheme. Norman has never received the recognition for this, because at the time the UK was in a recession, and ultimately Peterborough was sufficiently far to make a case for onwards electrification much more cost effective.

Changes to service frequency, together with much, much greater traction current demands by trains, and the operation of 125 mph loco hauled express services (never ever considered even during the extension to Peterborough) mean that there is much to be done in the GN area.

About 4 years ago a programme of headpsan refurbishment was started and then moved on to the renewal of the contact wires and retensioning of the system.

Mk 3 was never designed for more than 100 mph running, which is why the WCML was upgraded with a system known as UK1, a joint WS Atkins designed system.

 

[Aictos]

Cheers OT, once again a mine of information.

Okay. according to the Sectional Appendix for the LNE route it states that:

No more then 18 electric trains per line may be operated over the Hertford Loop in any one hour period.

A Class 86 may run on either the Up or Down line between Royston to Shepreth Branch Junction providing another Class 86 does not run on either line and no more the 2 8 4 Car EMUs allowed on the opposite line.
A 2 X 4 Car EMU may run on either line with not more then one Class 86 or 2 X 4 Car EMU is allowed on the opposite line.

 

[Royston Vasey]

I believe that the Royston-Cambridge section was electrified on the cheap in 1987 which meant it had limited power available.

A Class 86 may run on either the Up or Down line between Royston to Shepreth Branch Junction providing another Class 86 does not run on either line and no more the 2 8 4 Car EMUs allowed on the opposite line.
A 2 X 4 Car EMU may run on either line with not more then one Class 86 or 2 X 4 Car EMU is allowed on the opposite line.

Philjo, I see your point, but does this not merely mean it was spec'ed properly and fit for purpose for the use it would foreseeably receive? It would have been a potential huge waste of money to spec it for twice the number of trains each taking twice the power for example. Although upgrading was needed recently for 12 cars, this is 20 years after initial electrification and it has been fit for purpose for all that time, by and large!

In the example of Cl86s, I'm sure they have done so at some point, but I lived by the branch for 4 years and never once saw or heard an 86 use it. This is chicken or egg, you might say, but there's nowhere useful for electric frieght to go beyond Cambridge (diesel beyond there anyway) so why pay to install upgraded OHL just to take it from Hitchin to Cambridge?

There is also no point in diverting 225s up the branch because they can't get to Peterborough from Cambridge anyway, and electrifying to that standard for the odd blockade would again be a rather extravagant outlay for relatively minor benefit.

However, as to Ajax103's OP, if you're talking upgrades to allow for reliability improvements, or increased use for regular service trains then absolutely the investment should be made as it makes operational and economic sense. The odd diversion is not IMHO a convincing argument though.

 

[Old Timer]

It is slightly unfair to say that the extension to Cambridge was done on the cheap.

At that stage money was (as always) tight and the OHL design was appropriate for the train service then operating.

In the case of electrification it is generally cheaper to upgrade in the longer term provided that there are no major changes required to the fixed infrastructure.

You neeed to consider electrification akin to having a new computer, slightly down-specified to what you really want in the long term, but which you can upgrade as and when you get the money.

 

[O L Leigh]

The use of Cl86's on the Shepreth branch is limited to light engine movements only.

Quite why this was specified I couldn't say beyond speculation that it may have had something to do with positioning locos for the former loco-hauled West Anglia services from Cambridge into Liverpool Street, or possibly just that a single light Cl86 draws no more power than 2 x Cl317's. It certainly wasn't to permit any electric loco-hauled services along the branch.

O L Leigh

 

[Royston Vasey]

The use of Cl86's on the Shepreth branch is limited to light engine movements only.

Quite why this was specified I couldn't say beyond speculation that it may have had something to do with positioning locos for the former loco-hauled West Anglia services from Cambridge into Liverpool Street

Sorry, I did understand this from Ajax's post, I meant to say that installating OHLE to allow light engine movements is sensible, but spending any more money specifically to allow electric freight would have been a waste.

 

[O L Leigh]

Fair enough.

O L Leigh