769450 Flex at Southport 170521 TM1

UK: Considerably later than envisaged, Northern’s first Class 769 bi-mode multiple-units entered service with the start of the new timetable on May 17.

Modified from Class 319 dual-system EMUs formerly used in southeast England, the electro-diesel trainsets are initially being deployed on the Southport – Alderley Edge route, as well as some services between Southport and Stalybridge.

The trains are able to use either a 25 kV 50 Hz overhead power supply or newly-fitted MAN diesel engines. The design is seen as particularly well suited to those partially-electrified routes in northwest England which had previously required DMUs to run ‘under the wires’ for sustained periods.

The Class 769s are cleared to change between electric and diesel modes at a number of locations including Bolton, Manchester Victoria and Salford Crescent. The changeover is intended to be very rapid, with no extension to station dwell times or need for pre-heating of the diesel powerpacks.

Northern’s first revenue service to be worked by a Class 769 was the 05.50 from Wigan North Western to Alderley Edge; 769 450 departed in diesel mode and became the first set to switch power modes in passenger service when it made a 1 min stop at Bolton.

769442 Flex at Ashton-under-Lyne 170521 TM2

Observers on the initial runs reported some localised wheelslip issues caused by the relatively harsh weather conditions, but the trains were able to keep to timings without any difficulty. This is despite a late decision by Network Rail not to allow the trains to run at their 160 km/h design speed in electric mode. This is reportedly because of a cautious view of track impacts resulting from the additional mass being carried on the driving cars of each four-car unit; the diesel powerpacks add around 7∙5 tonnes to the weight of these vehicles. As a result, the 769s will be limited to 120 km/h in both modes.

‘Flex’ finally comes to fruition

Known as ‘319 Flex’, the programme to rebuild redundant Class 319s displaced from Thameslink services as dual-mode trains for Northern began as long ago as 2016, with the formation of a partnership between the operator and leasing company Porterbrook.

The initial plan envisaged conversion of eight sets to bi-mode operation to mitigate the effects of cancelled electrification schemes, including the section of route from Manchester Victoria to Stalybridge.

Porterbrook worked with Wabtec’s Brush Traction arm to develop the refurbished vehicles, but the work proved significantly more challenging than anticipated, leading to substantial delays. One insider told Rail Business UK that the project had taken in excess of 45 000 engineering-hours and used more than 3 500 new components. Others have attributed the delay to a decision not to involve original traction equipment and software supplier Alstom in the conversion.

Class 769 cab additions

Two MAN D2876 engines rated at 390 kW are fitted to each Class 769. These feed power via an alternator into the existing 750 V DC bus previously used for third rail operation. One challenge facing the engineering teams has been to balance the output of the two powerpacks, which has proved to be more complex than expected.

Initial reports from drivers indicate that the units’ performance is slightly better on diesel power than that of a Class 150 DMU, although acceleration is understandably slower in diesel operation than in electric mode. Trials indicate that the trains will have a range of around 960 km in diesel mode, which is substantially longer than the diagrams on which Northern intends to deploy them.

‘We are really proud to be involved in this pioneering development’, said Northern Trains’ Regional Director Chris Jackson. ‘Bi-mode trains bring the benefits of railway modernisation to more customers, more quickly. Northern is determined to make a positive impact for the north of England and this technology opens up new opportunities to spread the benefits of electrification to non-electrified routes, delivering more efficient journeys and increased capacity for our customers.’

‘The introduction of the Flex fleet into traffic is the result of a collaborative partnership between Northern, Porterbrook and our suppliers’, added Mary Grant, CEO of Porterbrook. ‘I would like to thank Northern for their unstinting commitment to the successful introduction of this highly innovative fleet, as well as my own team for their relentless focus on the needs of our customer.’

  • · The first of nine Class 769 electro-diesel multiple-units converted from Class 319 EMUs entered service with Transport for Wales Rail on the Rhymney – Cardiff – Penarth route in late 2020. However, these are operating solely as DMUs, with the pantographs removed. GWR has recently started to take delivery of 19 tri-mode Flex units which retain their third-rail DC capability.