For those who don't have access to NIR-online - it has been determined that a faulty VCB (vacuum circuit breaker) was the most likely fault. In this instance, the VCB is a part that is found on virtually all British Rail AC EMUs and AC electric locomotives designed and built in the 70s/80s.
Not just 70s and 80s... I went on a Pendolino with a couple of one-time pendo fleet engineers: we were sat in coach H (for horrible.) At every neutral section there was a bang as the power was cut out and then two more distinct bangs as two circuit breakers operated. It gave them great pleasure to hear, it really annoyed me, to the point that I usually try to avoid the S end of that coach! I don't understand why the two breakers operate as the power is re-connected - that's if I understood what was happening correctly.
I should have been more specific - this particular type of VCB is one that is found on 70s/80s era AC electric vehicles. The two "breakers" that you heard operating are a more modern type of VCB.
The 769 I was on yesterday ran on Diesel all the way to Levenshulme (at which point I got off rather than them do a power changeover) so has it only been sorted today?
Was this fault specific to a single 769, but a common part to all 319/769s and more? Modern units like 397s also have circuit breakers serving the same purpose but I’m unaware if they’re of the same type.
So it appears that the ban on the use of AC mode was perhaps an overreaction to the original incident. Someone jumped to the conclusion that the 769 design was to blame despite the lack of supporting evidence that it was anything other than a one-off fault.
Aside from being an overreaction, it was always completely illogical. In AC mode, a 769 has no components in use which are not common to 319s. If anything they should have been banned from running in Diesel mode. The unit that ran out of fuel (424) is still at Southport, still has no fuel in it and can’t be driven back to Wigan with the leading cab on the dead unit. The rescue unit (446) which it is still coupled to will have to run around, or it will have to run back as a 12 car with another unit at the front and this movement will obviously have to wait until after the strike.
Apart from when you know the original belief was that a different part of the traction system was to blame (which was modified during the conversion). So with the knowledge at the time it was the right decision.
That's exactly what happened here - the track circuits on the signaller's panel were flashing on and off, not just on the line on which the 769 was standing, but also on adjacent lines. That's very serious. Plus there was concern over why the VCB should have opened (even though it didn't) - possibly some sort of power surge - which needed investigation. So I think it was the right decision to restrict to diesel while the investigation was ongoing.
Would it not be possible to change out the dead batteries on 424 to enable multiple working? Then 446 could propel it back to Springs Branch for refuelling.
As reported earlier in this thread, the original incident was on 30th April. The ban on use of AC mode was introduced on 23rd May and rescinded on 20th June.
I'd say we keep driving the minor issues out of the 769s, give them an interior refresh and use them to reduce the shameful practice of creating CO2 from diesel oil whilst running under OLE.
Would this be easier than physically running round to ensure that the leading cab was on the live unit? What would happen if these batteries also ran out en-route to Wigan or even on the WCML?
And this after a full year of seamless bi-mode running…
This is completely unnecessary. There is already access virtually to the Mersey from Edge Hill via the Wapping Tunnel. Also Lime Street has had a through platform since 1977.
Likewise Voyagers.
769s (and 319s for that matter) are crap, yes. However, what does 66s running under wires have to do with one attempt to remove diesel under wires? Nice bit of whataboutism.
I'm not sure the poor Mersey deserves being filled with those old relics!
Not only are they crap but they were always crap. What sort of EMU is purely friction braked, even if you forgive the steel body, single motor car and Ashbourne seats?
I’m sure they’d be washed out to sea if they were dumped in the Mersey!
My understanding is that when power is lost, the train opens the breaker and then re-closes it when the power is determined to be back in specification. This reduces arcing and presumably also protects the train if it somehow ends up on a line electrified with the wrong voltage (I would imagine the results of applying 1500V DC to the input of the transformer would not be pretty).
Until recently, all of them?
You're right about the under/overvoltage protection, but at a neutral section the VCB opens before the neutral section and closes again after in response to automatic power control (APC) magnets which are located on either side of the running line and are detected by a receiver on at least one bogie of the train. At the first magnet the VCB opens, at the second it closes, a very simple system. So simple that if the magnet is missing after the neutral section, the VCB can stay open and the driver has to close it manually (by pressing a button in the cab). Or if the receiver detects a strong magnetic field anywhere it can open the VCB, as happened in the early days of 387s on GWR, when an AWS magnet on the up main at Acton caused the VCB on 387s on the down relief to open - took ages to work out what was going on there!
I suppose the comment is excusable if they weren't aware that all MK1 and MkIII EMUs had tread brakes, and have their motors concentrated on a single car.*
Disc brakes for the Mk3-based EMUs and the PEP-derived classes, but the point stands that these are still friction brakes.
A 9-car Pendolino has 3 VCBs, one for connecting each pantograph (on coaches C and H) and the third (also on coach H)to energise the transformer at the other end of the train via the 25kV roof cable (busline). The train runs with a single pantograph raised, usually the rear one.
Short answer, no
This is incorrect.
Perhaps the single motor car is a bad criteria, but many pre-Mk1 EMUs had dynamic braking before the war.
Yes, as well as being aluminium bodied, with 2 motor cars and seats preferable to Ashbournes. A vastly more advanced design. Their predecessors the 502s had rheostatic braking 40 years earlier, as evidenced by the 4 resistor grids mounted on the roof of the motor car and I believe the 506s could use regenerative braking on the Woodhead line, with resistor grids mounted on the substations. I don’t know if the 306s before conversion to AC and the introduction of TOPS could do the same between Liverpool Street and Shenfield given that it was part of the same LNER/BR(E) electrification.
There were a few experiments before the war with rheostatic braking but virtually all UK EMUs had tread brakes only. Both of the LNER 3-car sets (what eventually became 306s and 506s) had straight tread braking. The substation resistor banks were for the EM1s to dump excess power when descending with heavy coal loads.
