WITH rail operators striving to cut energy consumption to reduce their overheads, the European Union-funded research project Osiris, which concluded earlier this year, provided a leg-up to several initiatives to investigate improving the energy performance of key components.
Among the solutions profiled during Osiris' final conference held in Brussels on March 31 was a new auxiliary converter developed by Alstom in partnership with Milan Public Transport (ATM) and trialled on the city's metro Line 3.
The 17.1km line has 21 stations and is served by 45 trains operating under 1.5kV overhead catenary. Three types of rolling stock are used on the line: 34 of the original 1989-90 sets (or 1o lotto), five of these trains which have since been refurbished (2o lotto), and six AnsaldoBreda Meneghino sets, which entered service on the line in 2009.
Line 3 was chosen for the project due to the compatibility of the rolling stock with the proposed auxiliary solution, with a single six-car 2o°lotto train subsequently selected for the trial.
The train's existing single auxiliary unit weighs 1400kg, and offers a three-phase output of 2*33kVA and a dc output of 2*8.5kW. It has an efficiency rating of 82-90.1%. The enhanced auxiliary system solution was designed to improve this performance by utilising Silicon Carbide Technology (SCT), which is described by Mr David Hughes, Alstom's market and portfolio director, as "the key lever to reduce energy consumption in the system."
"We used the technology in real operating conditions to confirm exact improvements in reducing energy consumption that we could achieve in different operating conditions," Hughes says. "We found that the new converters offered significant energy savings as well as the added benefits of reducing the weight, volume, noise and maintenance needs of the auxiliary equipment."
The resulting system is split into two separate units which collectively offer a three-phase output of 2*60kVA and dc output of 2*20kW, an improvement of 100% compared with the existing units. The total weight of the converter is also reduced by 400kg to 1000kg, with a single unit weighing 500kg. The system offers an 87-93.7% efficiency rating, an improvement of 5.5% compared with the previous auxiliary converter.
To demonstrate this performance during the live trials conducted with ATM from November to December 2014, two of the four converters on a six-car train were replaced with the new system. Trials initially took place on a test track and then during night time operations covering a variety of simulations. These included consumption between stations and during station stops, a complete through journey from the first to the 21st station, and a complete day of operations, as well as with the HVAC systems turned on and off. HVAC consumption was also simulated for different passenger loadings - 33%, 66% and 100% - while tunnel temperatures, traction energy measurements, and passenger demands relative to different times of the year were considered to calculate an annual improvement rate.
The trials found that with a full load on the new converter, energy savings of 4% are possible, increasing to up to 7.4% with a smaller load, with the system calculated to produce an annual average saving of 5.5%. Overall the total direct annual energy saving was 237MWh when the train is operational, and 34MWh when stabled. As a result the total direct saving from improved efficiency of the system was 271MWh per year, with an indirect gain of 130MWh when HVAC consumption, substation and catenary loss are taken into account. The overall gain is therefore 401MWh per year.
Hughes says the major challenge faced during the trials was with electromagnetic compatibility (EMC) between the new equipment, the vehicles and infrastructure. "There were partial issues that had to be overcome through testing and validation resulting in tweaks to the design," he says. "This showed the usefulness of the demonstration project to highlight issues that were not anticipated in advance of the real-life project."
Other challenges were encountered from the frequency of operations and overall device availability. Indeed this was the first instance the new SCT-based auxiliary converters were trialled in a live setting. Hughes says that Alstom plans to continue development of the system following the conclusion of the Osiris project for the next two years in order to develop a product that is commercially viable.
He would not confirm whether the supplier is yet working with a partner on further development and commercial delivery of the system, but as the Milan tests showed, with the potential gains on offer, the benefits to operators could be substantial.