The Swedish Transport Administration is responsible for one of Sweden’s largest and most important electrical grids, with more than 11,000 kilometers of track and 1,900 kilometers of high voltage lines. In the new project, Metrum is delivering instruments and systems that contribute to reducing disturbances and losses in the grid, which leads to a more efficient and reliable railway.
“The traffic continuously increase and therefore also the energy consumption and the load on our network. The interaction between new vehicle types and our various installations of power supply is also a challenge we must deal with” says Mats Häger, technical specialist at the Swedish Transport Administration.
The railroad has a separate electricity grid in Sweden, and in Sweden and in certain other countries in Europe, the trains are supplied with power at 16.7 Hz instead of 50 Hz, in other words one-third of the normal grid frequency. The reason is historical – it was simply easier to build controllable engines for lower frequencies when electrified trains began rolling at the beginning of the 1900s.
Long distances and a complicated electricity grid structure result in frequent occurrences of temporary voltage variations in the grid. Moreover the loads – meaning the trains – are mobile, and the energy generated during braking must be received and fed back to the grid. The power flows are dynamic and in many respects there are similarities between the railroad’s power grid and the future smart grids, where larger amounts of locally produced electricity are expected.
The complexity is therefore substantial and to be able to handle the problems that arise, there must be continuous monitoring of how voltages and loads vary. On commission of the Swedish Transport Administration, Metrum has developed special instrument software that simultaneously handles both the 50 Hz and 16.7 Hz frequencies.
“With better information about both power flows as well as loads and voltage status, we have much greater opportunities to identify potential problems,” says Mats Häger. “Our proposals for corrective measures are also better based on facts.”
The PQ122 instrument, along with Metrum’s system for data collection and analysis – PQ Controller DB – enables the Swedish Transport Administration to maintain a good overview of disturbances at the various measurement points and at the same time slower variations can be followed and monitored.
Potential for increased efficiency
The Swedish Transport Administration’s electrical power is purchased from the major power utilities and is delivered as 3-phase high voltage electricity with a frequency of 50 Hz. Since the trains are powered with a single-phase 15 kV, 16.7 Hz electricity, the electrical power must be converted at converter stations. It is important to monitor the phases on the output voltages that are generated in the converter stations because this directly affects the power flows in the railway grid.
Metrum has developed an add-on module for the instruments that enables synchronized phase measurement at both 50 Hz and 16.7 Hz. By comparing the measured phases at various geographical locations, important information can be obtained about power flows and right actions can be taken to optimizing them.
“In the pilot project we’ve looked at a converter station in Skåne where the voltage was about nine degrees off on the 16.7 Hz side,” says Mats Häger. “By optimizing the phase we’ve been able to reduce annual electricity grid losses by 20 GWh, which corresponds to yearly savings of 10-15 million SEK. If similar measurements and actions are implemented throughout the country, there is likely significant potential for increasing energy efficiency.”
Certain converter stations in the Swedish Transport Authority’s grid have already been equipped for dynamic control of voltage phasing. In an ongoing pilot study the opportunities for further power flow optimization are evaluated – a prerequisite is that the phase angles and other parameters can be monitored in real-time.
“Collaboration with Metrum has worked out really well, among other things due to their promptness with respect to maintenance, operation and development of new functionalities. We now move on to supplementing the system with more measurement points for all important installations,” says Mats Häger in closing.