Co-operation with West European systems involves the necessity of satisfying a number of criteria put forward by UCPTE. Among them there are more rigorous recommendations concerning the rate of decreasing and increasing the power output, the reduction of the technical minimum of the power unit, shorter starting times and the sustained operation for the plant's own demand or idle running. Results of modelling the thermal and stress states of the turbine components during start-ups and fast cyclic load changes conducted according to UCPTE norms are presented. Influence of the load changes on the lifetime of the main turbine components (casings and rotors) was determined. Analysis was carried out for the high-power turbines.