The increase in traffic on existing tracks combined with new high-speed rail projects mean rail traction is fast becoming an important load on electrical supply grids. This in turn is focusing a lot of attention on voltage stability as well as the power quality of the surrounding grids. Trains taking power from the catenary need to be sure the supply voltages are stable and do not sag.
For the most common 50 Hz markets, power is taken between two phases of the feeding grid, thereby causing substantial imbalance between phases in networks originally not at all built for this kind of operation.
Voltage and current imbalances between phases of AC supply systems must be confined in magnitude and prevented from spreading through the grid to other parts of the system. Voltage fluctuations and harmonics need to be controlled if they are to stay within the stipulated limits. This is where FACTS come in.
Time as well as money can be saved by implementing FACTS in existing systems rather than investing in costly and time-consuming reinforcement of the railway feeding infrastructure, such as building new transmission or sub-transmission lines, and/or building new substations and feeding points.
It is also worth mentioning that with FACTS in the system, adequate power quality can be achieved with infeed at lower voltages than would otherwise be possible. This means, for example, that it may be sufficient to feed a railway system at 132 kV rather than at 220 kV or even 400 kV, which will of course enable a lower investment cost and also shorter implementation times.
FACTS for railways comprises SVC and STATCOM solutions.