Central Queensland Rail Electrification - Planning of Electricity Supply Facilities

Queensland Railways are proceeding with the electrification of the main routes in Central Queensland hauling coal from the Bowen Basin coal mining areas to the ports at Gladstone and Hay Point and Dalrymple Bay south of Mackay. The traction system will be supplied from single phase 132/50 kV transformers at each of 13 supply points, to provide a 25 kV catenary voltage and 50 kV supply to a feeder wire beside the track connected to 50/25 kV auto transformers at intervals along the track. The 132 kV short circuit levels at the supply points may be below 300 MVA while loads may reach short duration peaks of 20 to 40 MVA. As the load on individual transformers is random and distances between substations substantial the opportunity for balancing the phase loading is limited and negative phase sequence voltages could occur on the 132 kV system considerably in excess of the 1% to 2% limits commonly used for rotating machines. Static var compensators are to be installed at nine locations to reduce the unbalance caused by the traction load. This will be one of the largest applications of SVCs for phase balancing in the world. In addition the locomotives will use thyristor controlled drives, which will inject harmonic currents into the power system. Harmonic filters will be required to absorb harmonic currents from both the 50 kV traction load and from the static var compensators installed to balance the single-phase load. The planning of these electricity supply facilities will be described.