Tri-mode traction opens up new frontiers for UK freight


STADLER announced in July that it had finished manufacturing the body of the first Class 93 locomotive it is building for Rail Operations UK (ROUK) at its factory in Valencia, Spain, and is on track. to deliver the first locomotive as planned by the end of March 2023.

ROUK has ordered a first batch of 10 Class 93s under a contract for 30 of the Bo-Bo tri-mode locomotives signed in January 2021. The new locomotive type represents a major upgrade to its current fleet, and that the president of the ROUK group, Mr. Karl Watts, believes will help to transform its offer on the market.

The Class 93 is based on the Class 68 diesel-electric and dual-mode Class 88 electro-diesel locomotives built by Stadler for the UK market between 2013 and 2017, but with several key differences. Perhaps most notable, and a first for Britain, is the availability of four modes of traction: electric, diesel, diesel-battery and battery.

The tri-mode traction system consists of electrical operation at 25 kV 50 Hz ac, which offers an output of 4 MW in standard mode and an optional 4.6 MW tractive effort boost function. The EU Stage V compliant C32 diesel engine supplied by Caterpillar has an output of 900 kW, which is supplemented by 400 kW of additional power when operated with two supplied Lithium Titanate Oxide (LTO) power packs by ABB.

This is the first use of LTO on a UK locomotive and the batteries can also provide traction power on their own. Watts says this was not included in the original specification, but Stadler was asked to incorporate it, and he says it will prove beneficial in providing emission-free operation on non-electrified sections, including stations and tunnels, and noise reduction in sensitive areas.

Watts says the addition of the battery was the only design change required for the Class 93 from the dual-mode Class 88. However, he says there were challenges with this development. First, the weight of the initial battery system chosen would have taken the weight of the locomotive beyond 86 tonnes, limiting use on the UK network. There was also limited space in the locomotive to accommodate the batteries.


“Something had to give,” Watts says. “The compromise was the removal of the dynamic braking resistors. Dynamic braking uses the conversion of kinetic energy to provide traction motor braking. However, it converts this energy into heat through the braking resistors which is lost to the atmosphere. With zero energy recovery, dynamic braking offers little value beyond its marginal contribution to reducing brake shoe wear. The decision to sacrifice rheostatic braking resistors in favor of traction batteries, which recover kinetic energy, seemed obvious to me. It’s a matter of energy efficiency. »

Watts adds that using LTO on lithium oxide batteries provides a fast charge range of 10 to 20 minutes. The deviation depends on the source of the load, whether it is from the overhead line or the diesel set/alternator, as well as the ambient conditions and the age of the battery. LTO also has a technical charge range of 10-90%, which is higher than other battery types, which may only have 40-80%. The batteries have a lifespan of around eight years and Watts adds that they offer improved thermal management, although the cooling system still accounts for 50% of the battery’s weight.

The locomotive is fitted with both automatic two-line air brakes and an electro-pneumatic braking system, giving the Class 93 compatibility with a multitude of passenger trains. “No other locomotive in Britain is fitted with an EP braking system as standard,” says Watts.

The flexibility of the locomotive is also evident in the use of the CargoFlex coupler supplied by Voith, which is fitted with a Scharfenberg type 10 automatic coupler as well as a screw coupler, and is adjustable to all five drive heights. British coupling.

The coupling has a drawbar force of 850kN and has the capability to support digital automatic coupling (DAC), currently being trialed in mainland Europe, if and when the technology is adopted in Britain. Class 93 will use both a 42-way jumper cable socket and a UIC 558 jumper cable for data transfer. The locomotives are also ready for future upgrades to 5G telecommunications and ETCS.


Type testing will begin in November at Stadler’s Albuixech factory, where there is a short point-to-point test track, and move to Britain after delivery of the first locomotive in March 2023. The testing and online approvals are expected to continue through July, with the locomotive entering service the following month. Watts says Stadler is working in partnership with TÜV Rhineland on the certification and that a run on the Velim test circuit is not necessary because Class 93 is “90% based on Class 88.”

The use of ABB’s latest transformer in the AC traction system, which is equipped with insulated gate bipolar transistors (IGBTs), requires EMC compatibility testing. Testing is also required due to differences in dynamics and changes in the kinematic envelope when operating at the maximum locomotive speed of 177 km/h, compared to a maximum of 160 km/h on the Class 68.

As a result, the secondary air suspension has been improved. It has two coil springs and three hydraulic dampers on each side, four and six respectively on each bogie, which are supplemented by yaw and lateral dampers. Additionally, Watts indicates that a different traction motor gearbox was adopted from the Class 88.

“No other locomotive in Britain is fitted with an EP braking system as standard.”

Karl Watts

The improved performance of the locomotive is most evident in its very impressive wheel-to-rail tractive effort. Excellent acceleration gives the Class 93 a significant advantage over existing fleets; Watts says the Class 93 will be able to traverse the infamous Shap Gradient in Cumbria at 80mph where some freight traction is limited to 32mph.

While driving at 177 km/h is possible, it’s not optimal, according to Watts, due to the extra energy required and associated costs, especially in today’s climate. Instead, it favors a driving profile that matches the conditions at the time. As a result, he says the 4.6MW power boost is unlikely to be used as often, but will prove a good option when, for example, the Class 93 needs to maintain a high level of performance when It operates in mixed traffic on the West Coast Main Line.

He adds that the higher speed and flexibility of the locomotive will finally provide a viable argument for disrupting UK freight operations. In particular, he says that the train class system for giving priority to certain types of train over others when running, dating back to 1960, is becoming increasingly irrelevant and needs to be changed. “A freight train carrying high-value goods is much more important to the economy and society than a commuter train carrying a few passengers during off-peak hours, but right now we have to wait in a busy track. ‘avoidance,’ Watts says.

ROUK is a provider of ad hoc passenger and freight traction as well as UK network rolling stock movements, charter and traction operations to support infrastructure testing and monitoring. Class 93 could handle all of these activities. However, Watts says he is particularly excited about using the Class 93 to boost intermodal operations. He says he has the ambition to finally increase the maximum speed of these services on the network above 120 km/h, which dates from their introduction with the Freightliner service in 1965, which he says must change to bring in “The British Railway in the 21st”. century.”

It also foresees additional opportunities for Stadler in the UK market with the Class 93.

As part of the ROUK contract, it will decide whether to proceed with a second batch of 10 locomotives by December. It appears to be a formality and Watts says the order could eventually total 60 to 70 locomotives.

With many of Britain’s 650 mainline freight locomotives now approaching their 25th anniversary, notably the Class 66, ROUK is unlikely to be the only customer. Indeed, the locomotive has the potential to become the backbone of the freight fleet over the next few years, potentially heralding a new era of improved traction performance.


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