Taking a typical double extraction 330MW cogeneration unit as the research object

the variable condition model was built by applying the equivalent enthalpy drop method.On the basis of this model

the operation characteristics of this unit under pure condensing condition and extraction condition were investigated.The economic efficiency and peaking capacity of this unit under above two conditions were obtained.The results show that:under pure condensing condition

the low-pressure cylinder inner efficiency under 50% load condition was 71%

about 2.9% lower than that under 100% condition;the pure condensing condition had the strongest peaking capability(with a rate of 163MW)

but the lowest economy;the peaking rate of double extraction condition was only 79MW

which was the lowest;when one extraction flow rate was constant

the turbine power generation thermal efficiency increased with the other extraction flow rate.