Some 60 German-built trains caused carnage on the railways during a huge power cut by repeatedly shutting down despite the overhead wires lines working.
Thousands of rail passengers had their journeys delayed after major issues with the Class 700 and 717 Siemens trains operated by Thameslink in South East England.
The stock, built in Krefeld near Düsseldorf, ‘reacted unexpectedly to the electrical disturbance’ – and half of them required an engineer to be sent out to reset the train.
Passengers are taken off a Thameslink train following the major power outage on August 9
Govia Thameslink Railway said the overhead line voltage frequency had dropped, triggering a safety mechanism on the trains that caused them to shut down.
The operator said the train’s system was trying to protect its onboard computer and electronics, but Network Rail admitted the problem caused ‘significant disruption’.
It comes after a lightning strike on a transmission circuit followed by ‘almost simultaneous unexpected power losses’ at two plants caused blackouts on August 9.
An interim report found one million people were affected after outages occurred independently at Hornsea off-shore wind farm and Little Barford gas power station.
Commuters make their way off a Thameslink train from Highbury and Islington in North London after the power outage on August 9 caused it to stop on the tracks
The National Grid Electricity System Operator report said the scale of generation loss meant the level of ‘backup’ power required under regulations could not cover it.
As a result, the system disconnected customers on the network, with about 5 per cent of electricity demand being turned off to protect the other 95 per cent.
The power cut occurred just before 5pm on Friday August 9 and all supplies were restored by around 5.40pm.
The outage also stopped traffic lights from working, plunged Newcastle Airport into darkness and affected Ipswich Hospital.
Large swathes of the country including much of the train network was affected on August 9
Keith Bell, professor of electrical engineering at the University of Strathclyde, said the report raises the question as to what facilities Network Rail has in the event of power supply losses.
He said: ‘The event shows the need for and value of system defence measures. However, because it cannot be guaranteed never to trigger them, they need to be implemented in a cost-effective way that minimises the impact on critical supplies.
‘Operators of those critical supplies should, in any case, take steps to ensure sufficient resilience.’
The report found there were also eight signal power supplies in principally rural locations suffering minor outages, although this had little impact on passengers.
Two outages occurred at Hornsea off-shore wind farm and Little Barford gas power station
The interim report said: ‘Two almost simultaneous unexpected power losses at Hornsea and Little Barford occurred independently of one another – but each (was) associated with the lightning strike.
‘As generation would not be expected to trip off or de-load in response to a lightning strike, this appears to represent an extremely rare and unexpected event.’
The report said the lightning strike was one of many that hit the grid on the day and strikes are ‘routinely managed as part of normal system operations’.
It said protection systems ‘operated correctly to clear the lightning strike and the associated voltage disturbance was in line with what was expected’.
Trains at London St Pancras were held on August 9 while power was restored to the station
Industry regulator Ofgem said its investigation would examine the grid’s requirements to hold sufficient back-up power to manage loss of generation supplies, how generators met their obligations with respect to the transmission fault and whether distribution network operators complied with their obligations.
How Thameslink’s Class 700 is Britain’s first self-drive mainline train
The Siemens Class 700 Desiro City trains are Britain’s first self-drive mainline train and have been operating on the Thameslink network since 2018.
The Thameslink Class 700 Desiro City train
One of the trains took its first driverless journey in March last year, using an automated system to accelerate and brake as it travelled from Peterborough to Horsham.
The technology allows trains to run more frequently by optimising their speed, but a driver remains in the cab to carry out safety checks and close the doors at stations.
The trains, which are part of the £7billion Thameslink Programme, have been manufactured at the Siemens factory at Krefeld in Germany.
The number of services between St Pancras and Blackfriars is increasing to 24 trains per hour in each direction by December next year.
This means there will be a train every two to three minutes, which is a frequency never previously achieved on Britain’s railways.
However, the trains have faced varying complaints from passengers, with some saying the seats are too hard and others claiming they are too hot even in winter.
Passengers were even encouraged to bring their own cushions on the trains after the seats were likened to concrete.
Govia Thameslink defended their introduction by claiming seat designs are limited by fire safety standard.
The watchdog also said it would be ‘looking at whether the companies made the right decisions both in the numbers of customers disconnected and whether those customers disconnected were the right ones’.
Ofgem said it was liaising with the rail regulator and rail authorities ‘to understand better why the drop in frequency on the energy network led to disruption for passengers’.
The 5 per cent cut, a mechanism known as low frequency demand disconnection (LFDD), is generally understood to try to avoid disruption to critical infrastructure such as hospitals and transport networks and is usually evenly spread across Britain.
Welcoming the report, a National Grid ESO spokesman said it is ‘right and proper’ to have a full investigation into ‘the performance of the electricity system, and subsequent significant disruption to transports networks and critical infrastructure’.
Investigators are looking at National Grid ESO, National Grid Electricity Transmission, 12 distribution network operators in England and Wales, generators RWE Generation (Little Barford Power station) and Orsted (Hornsea) to see whether any breached their licence conditions.
Ofgem has the power to fine firms found to be at fault up to 10 per cent of their UK turnover.
Jonathan Brearley, Ofgem’s executive director of systems and networks, said: ‘It’s important that the industry takes all possible steps to prevent this happening again.
‘Having now received National Grid ESO’s interim report, we believe there are still areas where we need to use our statutory powers to investigate these outages.
‘This will ensure the industry learns the relevant lessons and to clearly establish whether any firm breached their obligations to deliver secure power supplies to consumers.’
Steve White, chief operating officer of Govia Thameslink Railway, said: ‘Modern trains are very safe and have features not found in earlier generations of rolling stock.
‘A preliminary investigation has established that there was a drop in the frequency of the overhead line voltage during the National Grid power failure on Friday, August 9.
Passengers wait for trains at Farringdon station on August 9 following the power outage
‘This triggered a safety mechanism on all operational Class 700 and Class 717 Siemens Desiro City trains which caused the trains to shut down, protecting the onboard systems and electronics.
‘Of the approximately 60 Class 700 and Class 717 trains operating on overhead power supply at that time, half were restarted by the driver following restoration of the power system to the correct frequency and the remainder required a technician to complete a reset.
‘Siemens Mobility Limited and GTR have set up a Task Force to analyse how these trains reacted to being exposed to this rare power supply condition.
‘Following a detailed review, recommendations will be made to minimise the impact of any similar incidents in the future. We will ensure that any appropriate lessons are learned and shared with industry partners.’
The final report is due to be submitted to Ofgem by September 6.
National Grid chief executive John Pettigrew was given a pay rise of almost £1million this financial year, earning £4.56million, up from £3.65million the previous year.
The remuneration committee, according to the firm’s annual report, said he had ‘continued to deliver strong performance in his third year in the role’.
Network Rail network services director Nick King said: ‘On behalf of the rail industry we would like to apologise for the disruption passengers faced on Friday, August 9.
‘There was a major national grid failure. This caused a short term loss of power to our signalling system and power supply equipment across a wide area of the rail network.
‘Fortunately the back up systems kicked in, but essential safety requirements did mean some disruption on several routes.
‘Unfortunately one particular fleet of trains had a major systems failure as a result of the national grid failure.
‘Many of these trains were unable to restart on their own and had to be attended by an engineer and this caused significant disruption across parts of the network.
‘We worked flat out with train operator colleagues and the British Transport Police to safely get passengers off impacted trains.
‘We have been working closely with National Grid, Government and the wider rail industry as part of a major review into what happened.’