Increased demand on existing interconnected power systems, together with the tightening of both operational and economic constraints, has led to the optimisation of maintenance and expansion planning becoming more critical. The planning task requires consideration of many often indeterminate variables and constraints, such as projected system loading, generation bidding strategies, plant capacity and environmental factors. The expert system presented here attempts to aid the knowledge intensive task of analysing and solving transient and steady-state problems associated with hypothetical network configurations. This enables the planning engineer to assess the operational viability of proposed maintenance or expansion plans.