The problem
Driven by economical and environmental concerns, the provincial authorities I Queensland, Australia have electrified a vast railtrack system. The railway traffic is mainly heavy coal haulage as the area is more or less unpopulated. The electrification is based on single-phase tapping of traction power at a number of points in the main transmission grid. As such it constitutes a source of voltage unbalance and harmonic distorsion on the main grid. The total traction load is of such a magnitude that countermeasures had to be introduced in order to preserve adequate quality of the main transmission grid voltage.
The solution
The FACTS options was selected as the most suitable countermeasure and during 1987, ABB installed a total of nine Static Var Compensators (SVC) for Powerlink of Australia in their 132 kV grid feeding power to the extensive railway network. The principal objective of these installations is to achieve dynamic load balancing for symmetrizing purposes as seen from the 132 kV network.
The nine compensators have an overall dynamic rating of more than 600 Mvar, making this installation the most comprehensive of its kind in the world. Together with the SVCs, a total of 28 single-phase harmonics filters were supplied as well, for the purpose of filtering of harmonics generated by the thyristor drives of the coal hauling locomotives.
It shall be noted that also the three-phase grid was built as part of the railway electrification. In this context, FACTS made it possible to operate the system at 132 kV. The grid owner Powerlink evaluated the alternative to use 275 kV but this was found to be more costly, although a large portion of the SVCs would then not be needed.