Abstract A relation belween the critical values of coal-saving and operation conditions of turbine units in cogeneration plant was studied.With a law of criti cal values of coal-saving proposed
a theoretical basis of the critical values of coal saving was laid for analysing and calculating the amount of coal to be saved.The turbine generating uint studied is C50-8.82/0.118 and the substituting units are the condensing units with different steam condi tions.