Unquestionable energy bills for trains and subways
Interview with Domenico Giordano
In the energy sector, we can find many examples of measurements facilitating global trade. Let’s see, in details, the energy used by trains and subways. The European research project MyRailS, coordinated by INRIM, aims at providing accurate measurements of energy used in the railway system to establish the correct amount of the bill, which is always a sensitive issue!
Domenico Giordano, the INRIM researcher who is leading this project, explains MyRailS’ contribution to the global trade.
Giordano is an engineer working in the INRIM Department for Advanced Materials Metrology and Life Sciences. His research activities focus on the development and characterisation of systems and voltage/current transducers for calibration and power quality measurements on medium voltage grids and railway supply systems, on the calibration of energy meters for on-board train installation, and the study of ferroresonance phenomena.
Engineer Giordano, what does the research project you are coordinating do?
MyRailS has many objectives. The extended name of this project tries to sum up them all: Metrology for Smart Energy Management in Electric Railway Systems. We want to understand how to manage energy better, avoiding wastes. The ultimate goal is energy-saving - recovering, for instance, the energy that trains and subways produce while they are braking - and the consequent reduction of CO2 emissions in the atmosphere. Since energy saving starts with the awareness of real consumptions, one of MyRailS goals is to improve the measurements of energy used by trains and subways. As for direct current (DC) measurements of electricity and power, there are no common references and a Europe-wide shared directive. Both are needed to perform not only measurements but also legal and globally recognised calibrations of measuring instruments.
In the railway field, accurate energy measurements seem to be not so important. Why?
It’s been like this so far, but things will change soon: the cost of energy will no longer be a lump sum. By 2022, it will be based on actual consumption. A precise and unquestionable measure of energy consumption is more and more required also because the railway market has profoundly changed. It does not show a unique manager anymore. Instead, it introduces many companies in competition, including those supplying the railway infrastructure, those delivering energy, those providing means of transport.
The metrology gap concerns especially DC energy and power measurements. In this field, shared references are still missing because, until recently, the energy was delivered and measured only in alternating current (AC). Today, however, not only 40% of railways but an increasing number of energy distribution networks, as well as charging systems of electric cars, use DC. Therefore, an update is necessary, and INRIM is one of the Metrology Institutes more active on this topic.
What is MyRailS doing to obtain accurate DC energy measurements?
INRIM has developed a system to calibrate the energy meters on trains running in DC. This system reproduces voltage and current conditions recorded during campaigns of measurements carried out on the railway lines of Piedmont. However, MyRailS does not neglect AC measurements: other partners in the project are dealing with them! The goal is to obtain reliable measurements through techniques and measuring instruments validated both for DC that is a new research field and for AC, where studies are more consolidated.
What results did you expect from the measurement campaigns carried out on Piedmont’s railway lines?
The purpose of the campaigns was to collect data. Now, we have a massive amount of information. Thus, we learnt how much energy that trains produce while they are braking we could recover. We can identify the most efficient speed profile. We measure energy and power quality more accurately. All these data are also of interest to international regulatory bodies, which define the standards and rules to be observed.
Therefore, measurements are not only quantitative. What is the impact of power quality measurements at the commercial level?
Power quality (PQ) depends on the current and voltage. Careful management of the tension helps to reduce wastes. Let’s see how. The voltage on railway lines decreases with the increase of trains in transit, like water pressure inside an apartment building when everyone takes a shower. To ensure the energy required by trains on the move, the railway network manager usually tends to raise the voltage. This increase conflicts with the interests of the train operator, who, to recover the electricity produced by braking trains, needs the energy not to exceed a certain warning level. If the voltage exceeds this limit, the energy generated is dissipated as heat through the braking rheostats. Thus, it cannot be recovered by the reversible substations (which can transfer energy from the train to the supply line). The measurement campaigns in the Madrid Metro have proved that. The Madrid Metro is one of the industrial partners of the MyRailS project, alongside others such as Trenitalia and RFI, the Italian Railway Network. The measurements performed in Madrid have shown how the recovery of energy produced by the braking trains is not complete due to a too high level of the supply voltage.
Measurements to promote energy saving, shared techniques and tools for an accurate evaluation of energy consumption, support for standardisation activities and definition of standards at a global level, etc. The MyRailS project promises a wide range of applications!
And that’s not all! The use of the same instruments to evaluate energy consumption will also be a step towards the interoperability of the European rail system - another contribution to global trade.