System load control

This means that the newest and most economic generating plant cannot all be operated at full output for 24 hours per day. Consequently hydro and less efficient steam plant has to be scheduled to operate for brief periods per day to carry the excess load above that of the base-load plant (See Fig. 22). Daily forecasting, however, is an inexact process, being affected by vagaries of the weather, industrial disturbances and other factors. It is in this area that hydro plant is most effective, because it can be brought into service in minutes, (or seconds if some warning has been given). The Snowy Mountains Scheme is ideal for this role in relation to the Victoria and NSW systems, and according to its annual reports it is called upon for sudden generation in substantial amounts very frequently, e.g. 137 times in 1980-81 and 133 times in 1981-82. Moreover, hydro plant can be loaded far more quickly than steam plant, in which load increases must be monitored closely against thermal expansions.

A substantial part of the overall cost of a generating body is the capital charges it must carry for spare plant. The availability of the very large steam driven units now in use has proven to be little better than 70 per cent, so coverage for routine and unplanned outage must be made. An inquiry under Sir David Zeidler was set up by the Federal Government in 1980 to examine the case for interconnection of the power systems of the eastern States, in part to share spare plant capacity. NSW and Victoria had been interconnected since 1959 through the Snowy Mountains Scheme, and had benefited greatly thereby, apart from the peak load contribution from the hydro plant. The Zeidler inquiry found that there was appreciable merit in adding an interconnection between South Australia and Victoria, and this is now being constructed (1987).

In 1986, the NSW Government set up an inquiry under Mr. Gavan McDonell into various matters concerning generation in that State, and found that the amount of spare plant was excessive (due to load growth falling behind forecasts) and recommended a slow down of new power station construction, having regard both to the latest forecasts, and to the benefits of interconnection with other States.

Australian Academy of Technological Sciences and Engineering