The interruption of train traffic for almost 15 hours on Monday, 30 June, on the Madrid-Andalusia high-speed line has already been explained. Adif has revealed this morning that the incident occurred after the catenary contact wire melted due to the accumulation of trains.
All this was the result of a combination of an Ouigo train failure, which had some bearing on the events, and an electrification design problem that Adif AV has committed to fixing next week.
According to Adif’s information, the area where this issue occurred has been declared sensitive due to its configuration. A melting of the wire also caused the “snagging” of 4 May by an Iryo train.
However, the infrastructure manager has only been able to determine the causes of this incident this week, as they claim that the Spanish-Italian operator did not provide the necessary information.
Accumulation of trains and an overcurrent that killed the contact wire
Let us review the events of Monday, 30 June.
The difficulties began when an Ouigo train, 06598, covering the Madrid-Malaga route, experienced issues with the onboard LZB equipment. LZB is the safety and signalling system used on this line.
According to people travelling on later trains, these issues forced them to slow down, and there were several stops along the way.
In one of these stops, as Adif explains, four trains came together on a 7-kilometre stretch of catenary.
This means that four trains are generating a simultaneous energy demand on the same set of contact wires. A demand that is also greater than usual due to the power that the air conditioning equipment needs to combat the heat wave.
According to Ohm’s law, as the current increases, the resistance increases, and this increases the temperature of the contact wire.
According to some sources, the triggering factor for the melting of the contact wire and the crash on Avant 08190 was the consumption generated by the engines when they restarted.
Other sources claim that the train was stationary at the time, so the overheating may also be a consequence of the pantograph being fixed at the same point, resulting in high energy consumption.
As the contact wire exceeded its design temperature limit, it eventually melted, causing the catenary to fall onto the train.
The relocation of the isolator will prevent this from happening again
In its note, Adif explains that the immediate solution to avoid this problem from recurring in this area is to relocate a catenary section isolator between 600 and 900 metres.
This device, which is vital in electrification, isolates catenary areas. In other words, it splits the catenary into sections in order, among other things, to avoid these overcurrent issues.
Although the infrastructure manager has not yet clarified this, it appears that the section of catenary affected coincides with a track block. Track blocks are divisions of a railway track delimited by signals, created to prevent a train from overtaking another train from behind.
On the Madrid-Andalusia HSL, they have little real use, as the LZB system uses its blocking system, which allows more trains to enter a fixed block section delimited by signals. However, the Ouigo train, which ran without LZB (using ASFA instead), did utilise traditional signalling.
The main problem with the catenary section coinciding with a track canton is that if a train is stopped at a signal, the following trains (which in this case can safely invade the canton) are supplied with power from the same catenary section.
If this section of the catenary is not prepared to withstand the current peaks of all trains that can use it simultaneously, it will melt.
By displacing the disconnector, a stop at a signal is prevented from causing the same problem as Monday.
However, if, for another reason, a train is stopped at the end of a catenary section and more trains accumulate on the same section, and the system is still unable to cope with the demand, this will happen again.