How does a combined cycle power plant achieve high efficiency?

A combined cycle power plant integrates a gas turbine (Brayton cycle) with a steam turbine (Rankine cycle). Hot exhaust gases from the gas turbine pass through a Heat Recovery Steam Generator (HRSG) to produce steam for the steam turbine. This cascading arrangement utilizes energy at both high and low temperature levels, achieving thermal efficiencies of 55-62%, compared to 35-40% for simple cycle plants. The gas turbine contributes about two-thirds of total power output.