Yesterday, passengers travelling with @SouthernRailUK , @TLRailUK + @GatwickExpress endured an awful evening after we lost the ability to run trains on the busiest part of our network, shown in the picture, for over an hour.
Here is what happened... 1/
Here is what happened... 1/
@SouthernRailUK @TLRailUK @GatwickExpress At 4.24pm, every signal in the area turned red and trains stopped across the whole area. Trains soon stacked up + we worked with our operator colleagues to move them into stations as soon as possible. It soon emerged that 3 signal control locations had shut themselves down. /2
@SouthernRailUK @TLRailUK @GatwickExpress Each location had to be manually reset, which took us until 5.47pm, when our signalling was fully restored. We then worked with our colleagues to get trains moving again and try to get a stable service plan in place to get everyone home from London. As you saw, this took time. /3
@SouthernRailUK @TLRailUK @GatwickExpress We can only apologise for what was a terrible evening for our passengers, who took hours to go home and in some cases missed flights from Gatwick Airport. Many of you asked us how this could happen - so this is what we know. /4
@SouthernRailUK @TLRailUK @GatwickExpress The power supply to our signalling in this area had a power surge, what is known as an Over Volt, for 20 seconds. This is an unusually long time for that kind of surge and many different systems - some only 18 months old - all shut down to protect themselves. /5
@SouthernRailUK @TLRailUK @GatwickExpress This display is what the signalling control system at East Croydon should look like, but last night it was competely blank. It's where the electronic signals from the control centre at Three Bridges are processed and sent out to the tracks to move points and change signals. /6
@SouthernRailUK @TLRailUK @GatwickExpress Our technicians went to four different locations across the Croydon area and manually reset them, which fixed the problem and allowed trains to run. Had those systems not shut down they would all have been damaged by the surge. /7
@SouthernRailUK @TLRailUK @GatwickExpress In fact it is unlikely we would have been able to run a service today either as every location would have needed to be repaired or replaced. So the systems worked as designed and saved us from a much worse fate. /8
@SouthernRailUK @TLRailUK @GatwickExpress So why didn't the backup kick in? We have three separate power supplies to our signalling to stop this from happening, + they are designed to switch over when the power is cut. But the power stayed on, just at the wrong Voltage. /9
@SouthernRailUK @TLRailUK @GatwickExpress Why don't we have Uninterruptable Power Supplies? Well, we do at some locations, such as signalling centres. What we are not sure of - and are investigating - is if a UPS at each location would have stopped this or if the voltage spike would have put them offline too. /10
@SouthernRailUK @TLRailUK @GatwickExpress A UPS at a nearby location actually put itself into "bypass" during the spike, which suggests it is not a clear-cut answer. Another important part of the investigation is why we cannot remotely reset signalling control points, and how quickly that can be rectified. /11
@SouthernRailUK @TLRailUK @GatwickExpress So what is next? We are working with our operator colleagues to investigate the disruption, with @UKPowerNetworks to learn more about the power surge + our many signalling suppliers about how we can make our kit more resilient to this kind of event. /12
@SouthernRailUK @TLRailUK @GatwickExpress @UKPowerNetworks Finally, we can only apologise for the disruption last night, as we know what a huge impact it had on everybody. When the full investigation is complete, we will let everyone know what it finds (beyond what we know so far) and how we will make things better in future. /13
@SouthernRailUK @TLRailUK @GatwickExpress @UKPowerNetworks Our boss John has posted this on our website, which has a more detailed look at the technical aspects of what went went wrong. We know this won't make up for yesterday but we hope it helps your understanding and shows how seriously we take this. Thank you. networkrail.co.uk/running-the-ra…
