Power failure on wokingham-Reading line, 27 Nov 2017

[whole diary]

[stuving]

According to SWR^» (South Western Railway - about), last night one of their trains ran out of juice and got stuck between Wokingham and Reading.  I can't see where, exactly, from RTT^» (Real Time Trains - website) - GWR^▸ (Great Western Railway) trains to Reading were hardly affected, while those towards Gatwick waited so long they were cancelled from Guildford because they were so late. However, the one train that got so far and then disappears from the records was at Earley and heading for Reading; and there's little provision for passing or reversing trains there.

Since SWR took over, their excuse generator seems to have adopted a different style from SWT^▸ (South West Trains)'s. It is set up to explain more, and tells you "what's going on" and then "what we're doing about it", though with some variation (and often not putting things under the right heading). The same words are then used by National Rail Enquiries. Whether NR^» (Network Rail - home page)'s contribution is used verbatim, or is being "improved", I can't say.

So today we got:

Electric Supply Problems between Reading and Ascot
Due to an electricity supply problem and a points failure between Reading and Ascot some lines are blocked.  Train services running to and from these stations may be cancelled or revised. Disruption is expected until 12:00 today, 28 November.

What's Going On:
Last night, one of our train services reported a problem with the electricity supply to trains between Wokingham and Reading. This resulted in the electricity supply being switched off.

Network Rail, who own and maintain the railway infrastructure, sent engineers to site to inspect and rectify the fault. When they arrived on site, they discovered that numerous power cables had burnt out which needed to be replaced before our electric trains can again call at stations between Wokingham and Reading.

It is anticipated that Network Rail will complete their work at 10:00 this morning at which point we will aim to recover the train service. Prior to that time train services from Reading towards London Waterloo will start at Ascot or Wokingham and train services running towards Reading will terminate at Ascot or Wokingham.

At 07:10 this morning a points failure occurred at Wokingham and this has further hampered attempts to operate train services as far as Wokingham. Points are sections of track that enable trains to change from one line to another. This failure means that trains are unable to run between Bracknell and Wokingham and Bracknell and Crowthorne in either direction. Staff are on site working to repair the points but we do not currently have a firm estimate of when we expect this problem to be resolved.

Replacement road replacement transport is now in operation, we are working to extend the scope of the replacement transport due to the points failure.

For details of alterations to individual services please see our JourneyCheck page.

If you require assistance in completing your journey, please speak to a member of staff or use a help point at any station.

Train services will be subject to alteration or cancellations. We apologise for the disruption caused to your journey today.

How We're Helping You Complete Your Journey:
We have arranged for your tickets to be accepted on the following routes:

    Great Western Railway services via any reasonable route
    London Underground services via any reasonable route.

Actually, trains were back running well before 10:00, though obviously the whole morning peak was lost. The power for this section of track was beefed up a lot in preparation for our longer trains (still few of them around) and more of 'em (not until next year). So what burned out? It wasn't at one of those nice new feeder stations, was it? Or (reading across from other problems) some old cables that were disturbed in putting in the new stuff?

NRE^‡(resolve) added this about GWR services:

The diesel services can run between Wokingham and Reading but these are expected to be extremely busy.

However, after 7:00 they didn't - they waited on either side until after 9:00. And all  GWR Journeycheck had to say, other than listing those cancelled and delayed trains, was (for example):

09:02 Reading to Redhill due 10:25 has been cancelled.
This is due to a fault with the signalling system.

Nothing under "Line Updates".
"Under "Your Journey", it was just "Major disruption between Reading and Wokingham until 12:00 ".

Some of the individual part-cancellations appear appear in RTT with the usual puzzling attributions, such as "This service was cancelled between Guildford and Gatwick Airport due to a problem with the electrified line (I1)."

[Electric train]

Not really a SWR^» (South Western Railway - about) fault, I lead to believe it was a 1000mm² cable lug that burnt off, it also caused some other damage

[stuving]

Not really a SWR^» (South Western Railway - about) fault, I lead to believe it was a 1000mm² cable lug that burnt off, it also caused some other damage

That does sound like the kind of thing that the recent work could lead to. And old cable heaved about once too often, or a new one not torqued up or not clean...

[Oxonhutch]

... it was a 1000mm² cable lug ...

Now that's a lug!! Maybe I should say LUG!! By my calculation, that's a circular cross-section a millimetre, or so, shy of an inch and a half. Considering my ring main is 2 x 2.5mm² in size, I am in awe of the current that bad boy was asked to carry. And my house is only at 250V ...

[stuving]

... it was a 1000mm² cable lug ...

Now that's a lug!! Maybe I should say LUG!! By my calculation, that's a circular cross-section a millimetre, or so, shy of an inch and a half. Considering my ring main is 2 x 2.5mm² in size, I am in awe of the current that bad boy was asked to carry. And my house is only at 250V ...

But how much was that 1000 mm" CSA cable asked to carry? There's several ways to answer that ...

1). Obvious:  more than it could could cope with.

2). Disappointing: Less than you expect, if you think current scales with CSA - it rises far slower than that.

3). Prosaic: BS7671, though it excludes railway traction applications, lists several currents for 1000 mm² CSA cables, depending on their type and how well cooled they are; from 1154 to 2100 A.

4). Realistic: BS7671 lists constant currents, but a train can't draw maximum power for more than about a minute before it hits maximum speed and coasts. So the question is more like "how much current can that cable take for a minute at a time"?

A pair of 450s with the tap open wide wants 2.2 MW plus, say 3 kA. In reality the current profile's quite complex, so some proper thermal analysis is called for to tell you the answer. I'd guess that 3 kA would be OK, but my thumb is well out of calibration.

Oh, and the lug and terminal probably has a lower current rating than the cable, even if it's been made perfectly and not degraded, which needs to be analysed separately ...

[Electric train]

... it was a 1000mm² cable lug ...

Now that's a lug!! Maybe I should say LUG!! By my calculation, that's a circular cross-section a millimetre, or so, shy of an inch and a half. Considering my ring main is 2 x 2.5mm² in size, I am in awe of the current that bad boy was asked to carry. And my house is only at 250V ...

But how much was that 1000 mm" CSA cable asked to carry? There's several ways to answer that ...

1). Obvious:  more than it could could cope with.

2). Disappointing: Less than you expect, if you think current scales with CSA - it rises far slower than that.

3). Prosaic: BS7671, though it excludes railway traction applications, lists several currents for 1000 mm² CSA cables, depending on their type and how well cooled they are; from 1154 to 2100 A.

4). Realistic: BS7671 lists constant currents, but a train can't draw maximum power for more than about a minute before it hits maximum speed and coasts. So the question is more like "how much current can that cable take for a minute at a time"?

A pair of 450s with the tap open wide wants 2.2 MW plus, say 3 kA. In reality the current profile's quite complex, so some proper thermal analysis is called for to tell you the answer. I'd guess that 3 kA would be OK, but my thumb is well out of calibration.

Oh, and the lug and terminal probably has a lower current rating than the cable, even if it's been made perfectly and not degraded, which needs to be analysed separately ...

staving is partially correct, BS7671 does not have the insulation type used for traction cable, its not PVC but a rubber based product, the DC^▸ (Direct Current) positive track feeder cables are 1000mm² aluminium. To get a BS7671 rating you have to take into account the circuit protection type (circuit breaker / fuse characteristics), de rating factors for containment, Volt drop etc.

Traction cables are rated on the cyclical nature of the loading, typically the high speed DC circuit breakers are set for around the 4kA loading and 6kA for what is classed as a high current railway; high current or high reliability railways its normal for the tack feeder to be doubled (two 1000mm² cables).  The main circuit protective device is an impedance relay, this measure Voltage and current and compare the sum of these to an Ohmic value in its settings; this protection acts very quickly under fault conditions, the DC breakers also have a direct acting trip which is set to 10kA typically the breaker will clear a 10kA fault in 15mS

The cable also live a mix of open and exposed to ducted in under track crossing (when open and exposed of course they are subject to solar heating)

Over heating of positive DC traction feeder cables is not normally an issue, the lugs on the conrail end do suffer from the limited flexibility of the cable the movement of the track as the train passes, its aluminium bolted to steel; the designs for this interface a constantly evolving 

[stuving]

BS 7671 does, in fact, have a number 90^oC thermosetting insulation aluminium cables; but as noted above the tables won't give you a meaningful peak current capacity.

I did find some numbers for 458s: the rebuild gave them 6x270 kW motors per set in place of 4. That (plus the 4 tph timetable) is what led to the extra feeder stations being built. If the power controller is set to provide full motor power (and it may not need to), a train would be drawing about 5 kA. Now that could well make your lugs feel a bit warm.

[Electric train]

BS 7671 does, in fact, have a number 90^oC thermosetting insulation aluminium cables; but as noted above the tables won't give you a meaningful peak current capacity.

I did find some numbers for 458s: the rebuild gave them 6x270 kW motors per set in place of 4. That (plus the 4 tph timetable) is what led to the extra feeder stations being built. If the power controller is set to provide full motor power (and it may not need to), a train would be drawing about 5 kA. Now that could well make your lugs feel a bit warm.

It does and if the decision was taken not to fully implement a high current railway, it is quite costly to do at existing traction locations easier with ne build or replacement.  The conversion to a high current railway may be being phased in.

Lugs burning off is not uncommon, almost a daily occurrence somewhere on the system; it should be born in mind there are thousand of these lugs on the network