A method and apparatus is disclosed for converting a reheat steam turbine plant to a non-reheat, combined cycle plant without requiring internal modification of the steam turbine unit. A reheat steam turbine power plant with a boiler and a steam turbine with a plurality of turbine sections, receiving steam under pressure and successively expanding the steam through the turbine sections, is converted to a non-reheat combined cycle plant by replacing the boiler with a dual-pressure heat recovery steam generator capable of producing main steam and secondary steam at differential temperature and pressure and by installing a trimming system to allow adjustment of the pressure drop between the exhaust of the first turbine section and the inlet of the second turbine section to prevent damage to the turbine blades. The non-reheat cycle plant may also be operated with secondary steam supplied at the inlet of the final turbine section to reduce the moisture content of the steam thereby preventing excessive wear on the turbine blades.