Smart energy management solutions – how to take full advantage of braking energy
Railway and urban transport systems are mostly electrified and therefore a key to decarbonizing transport. It can be observed with interest that many operators are looking to become even more efficient and achieve further energy savings thanks to a wider use of smart energy management solutions.
This article demonstrates how an operator of a suburban railway network has further reduced its carbon footprint and became more energy efficient by introducing innovative technology.
Metro Trains Melbourne (MTM) has been experiencing continuous voltage drops in their DC grid due to a large distance between two traction substations, feeding a section of the Hurstbridge line from both ends. The operator was also looking to increase the frequency of train services on the line.
The voltage drops were causing instability in the DC grid and unreliability in train services. The most common solution would have been:
· to build a new rectifier substation providing additional power,
· to replace existing diode rectifiers with active rectifiers boosting the voltage,
· or to reinforce the overhead line infrastructure to reduce voltage drops.
However, the construction of a new substation would not guarantee an adequate level of traction power supply reliability, as it would have to be supplied from the same node of the medium voltage network as the neighboring substations.
Finally, MTM has chosen to pursue an alternative solution and contracted ABB for the design, supply, and integration of a static energy storage system Enviline™ ESS. It has been installed at the existing Diamond Creek tie station to inject power and to reinforce the 1500 V DC grid at its weakest point of the upgraded Hurstbridge line. Even with a relatively small capacity of 12.2 kWh, the traction voltage is now stabilized allowing the operation of the line with its full capacity.
The system stores energy gathered as trains brake as they enter the Diamond Creek station, before feeding it back into the grid as the train accelerates out of the station. The system is also capable to slowly recharge during no load periods.
The energy storage system was finally found more cost effective in terms of land use and construction, thus reducing the capital expenditure by more than 50% compared with a normal rectifier substation. It also resulted in a 15% reduction in carbon emissions and supplemented electricity drawn from the AC grid.
Static energy storage systems can be considered as an interesting alternative compared to traditional rectifier substations. Operators see the economic benefits of this technology while at the same time increase energy efficiency and reduce carbon dioxide emissions.
René Jenni - ABB Switzerland Ltd, Baden CH and Dr. Patrycjusz Antoniewicz - ABB Sp. z.o.o., Krakow PL