<p>Power plants frequently operate under off-design conditions, necessitating comprehensive performance assessments across varying load levels. This study applies energy, conventional exergy, conventional exergoeconomic, advanced exergy, and advanced exergoeconomic analyses to a three-pressure combined cycle power plant in Rudshur, Tehran, comparing full load (100%) and partial-load (75%) performance. At full load, the plant achieves high net power output and improved exergy efficiency, albeit with increased component cost rates and exergy destruction. Advanced exergy analysis identifies the low-pressure steam turbine as the primary source of endogenous avoidable exergy destruction, while the gas turbine incurs the highest endogenous avoidable investment cost. Under partial load, energy and exergy efficiencies decline by 2–3%, with proportional reductions in investment and exergy destruction costs, while the ratios of avoidable to unavoidable and endogenous to exogenous losses remain stable. Notably, the condenser assumes a greater share of investment cost at partial load, while the low-pressure steam turbine remains the dominant source of endogenous avoidable exergy destruction. To our knowledge, relatively few studies have integrated advanced exergy decomposition with exergoeconomic valuation across both full load and representative part load conditions for an actual three-pressure combined cycle plant. This work applies that integrated approach to the Rudshur power plant (Tehran) and identifies component-level thermoeconomic priorities under realistic load variation.</p>