When Clayton Equipment secured the contract from London Underground to convert a fleet of maintenance locomotives from diesel to electric power it asked EnerSys® to supply the motive power batteries. The battery manufacturer supplied cells from its Hawker® Perfect Plus range which were assembled into high-performance 210kWh packs to deliver the power needed to support a highly demanding operational requirement. “We use EnerSys batteries on many of our locomotives and try to pick a standard cell whenever possible because this simplifies sourcing and support,” says Clive Hannaford, operations director at Clayton Equipment. “Scheduling was vital for this project and EnerSys provided the products we needed on time and within our budget, including their installation and commissioning expertise.”

£2 billion upgrade and 24-hour running

The 14 locomotives being converted by Clayton Equipment to its CB40 specification were originally supplied to London Underground by another manufacturer for a project completed some time ago. The public transport operator wanted additional maintenance resources at its Ruislip depot to support a network currently undergoing a £2 billion upgrade and which will implement 24-hour running over the next few years. Maintenance windows – when passenger services are not running – for tasks such as track and signalling repairs are becoming shorter which means more engineering teams who need more equipment to complete their work. Operating the noisy, smelly and polluting diesel locomotives deep underground was not an option but converting them to battery-electric traction represented a cost-effective way to increase the rolling stock. Clayton Equipment has more than 75 years’ experience manufacturing and refurbishing narrow and standard gauge locomotives and specialises in electric units for underground applications including engineering and mining.

Advanced CAD and FEA tools as part of design process

It was awarded the contract by London Underground in 2014. Engineers from the company worked closely with colleagues from London Underground to finalise the specification and used advanced CAD (computer aided design) and FEA (finite element analysis) tools as part of the design process. The batteries were selected very early in the process. London Underground’s specification included a duty cycle which included the number of hours they will work on each shift, ability to haul 120 tonnes, negotiate 1:30 gradients and travel at up to 49kph. All of this must be achieved within weight and size limits for operations in the confined London Underground tunnels. Once all these and other factors were taken into account the designers calculated the amount of energy needed which led to the battery specification of 210kWh. The battery pack is housed in a removable frame. Space is limited and the pack, weighing eight tonnes, must be positioned carefully within the chassis to distribute weight evenly over both axles and ensure the optimum performance of the 40-tonne locomotive.

Range of standard DIN and BS sizes provide design engineers with flexibility

EnerSys produces its Hawker Perfect Plus 2V cells in a range of standard DIN and BS sizes to provide design engineers with flexibility when configuring bespoke battery packs. In this particular application the cells were chosen to make the best possible use of space within the pack to maximise capacity and output. Hawker Perfect Plus batteries perform extremely well in heavy duty applications where they provide high efficiency in discharge with their advanced designed positives plates. The plate size is optimised for the volume available in the cell boxes and the state of the art process used in filling the positive plates ensures optimum performance and service life. The cells are arranged as four equally-sized batteries inside the pack, each requiring its own charger. This configuration promotes better management, efficiency and reliability by enabling balanced charging and power consumption. Cells were delivered to the Clayton Equipment facility in Burton-on-Trent to align with the project schedule. Engineers from EnerSys then visited Clayton Equipment to install the batteries. They also installed the Hawker Aquamatic water topping system that allows all cells to be filled from a single point. “The EnerSys products have a very low failure rate as a proportion of the number we fit,” says Hannaford. “We try and use autofill wherever possible because it makes it much easier to maintain the batteries in the operating environment.”

Converting locomotive from diesel to battery involves more than replacing internal combustion engine with electric motors

Converting a locomotive from diesel to battery power involves more than simply replacing the internal combustion engine with electric motors. Clayton Equipment started by removing the diesel engine and gearbox although the original wheels were retained after refurbishment. Vital services such as the compressors for the braking system were relocated to a different part of the chassis to help spread weight more evenly and make better use of the available space. The locomotives have to work at a voltage which matches existing systems and the operability of the signalling systems had to be maintained. New electric motors were installed and connected to the wheels and power management system. Many of the electrical circuits have been upgraded and the cabs refurbished with modern facilities and information systems. The chassis have been completely refurbished and repainted in a new livery. “Space is so tight in most areas that only one engineer can have access at any given time,” says Hannaford. “We need efficient planning and management to ensure the conversion proceeds as quickly as possible.” The locomotives are designed to use power drawn from the batteries or from the live rails found throughout the network. Batteries are needed whenever live mains power is unavailable, for example when the locomotives are supporting track replacement or when the power supply itself is being serviced.

Multiple hot-shoe pickups that can be raised and lowered to take advantage of whichever live rails are available

Different configurations of third and fourth rail electrical systems are found across the London Underground and Overground network where the locomotives will operate. To accommodate both Clayton Equipment installed multiple hot-shoe pickups that can be raised and lowered to take advantage of whichever live rails are available. The locomotives’ control units work at high voltages and adapt to whichever power source is being used, delivering current to the motors from the live rail or battery pack as needed and to the on-board chargers. Energy recovered from the regenerative braking system is also used for battery charging. Because the locomotives are designed to operate in confined areas it was essential to install hydrogen gas monitoring equipment and provide compliance information to London Underground. “We needed to understand the gassing of the batteries and EnerSys provided detailed data which we incorporated into our documentation for London Underground,” says Clive Hannaford. “The technical support from EnerSys is always very good.” Each completed locomotive is put through a demanding pre-delivery trial at Wirksworth in the Peak District, chosen for its proximity to the Clayton Equipment factory and the gradients available to verify performance. As part of the contract the company has supported the approval process, including product acceptance, EMC testing and track testing. It has already – as of June 2015 - delivered more than half of the locomotives to London Underground’s Ruislip depot and the remaining units will be completed on schedule in the near future.