Based on the Flugel formula

an expression formula of the characteristic flow passage area in steam turbines has been given through mathematic deduction.Combined with one ultra-supercritical 600 MW unit

results of calculation show that the variation of deviation value concerning the characteristic flow passage area of every stage-group(not including stage-group no.7) is within ±1.5% when the unit is in operation under variable condition with 50%~100% rated load.Besides

the ways regarding application of characteristic flow pasage area in many aspects

such as the performance analysis in operation of unit

the establishment of thermal performance database of single unit

the calculation of variable operation condition

as well as the on-line monitoring and diagnosis etc.

have been pointed out.