Power plant comprising: - at least one gas turbine unit; - at least one steam unit provided with at least one first steam turbine (7a; 7b) rotating about a shaft and provided with a casing (9a; 9b) comprising a first lower casing and a first upper casing coupled together; - a steam generator supplied with exhaust gases coming from the gas turbine unit and configured to generate steam to be supplied to the steam unit; the steam generator comprising an exhaust fumes flow chamber in which the exhaust fumes of the gas turbine unit flow, and a steam circuit supplied with demineralised water and extending inside the exhaust fumes flow chamber, in such a way as to use the heat from the hot fumes coming from the gas turbine unit to generate steam to be supplied to the steam turbine unit; - a heat maintaining assembly for controlling the temperature in the steam unit during the shut-off of the plant; the heat maintaining assembly comprising: ▪ a first supply line (23; 38) configured to supply a first flow rate (Q1; Q2) of heated air into at least one first steam feeding conduit (28; 43) of the steam circuit supplying the at least one first steam turbine (7a; 7b); the first air supply line (23; 38) comprising a first blower (30; 44) and at least one first heater (31; 45); ▪ a first upper casing temperature sensor (26; 41) arranged outside the first upper casing and configured to detect a first upper casing temperature (TU1; TU2); ▪ a first lower casing temperature sensor (25; 40) arranged outside the first lower casing and configured to detect a first lower casing temperature (TL1; TL2); ▪ a control device configured to regulate at least the first blower (30; 44) on the basis of the difference between the first upper casing temperature (TU1; TU2) and the first lower casing temperature (TL1; TL2). - at least one gas turbine unit; - at least one steam unit provided with at least one first steam turbine (7a; 7b) rotating about a shaft and provided with a casing (9a; 9b) comprising a first lower casing and a first upper casing coupled together; - a steam generator supplied with exhaust gases coming from the gas turbine unit and configured to generate steam to be supplied to the steam unit; the steam generator comprising an exhaust fumes flow chamber in which the exhaust fumes of the gas turbine unit flow, and a steam circuit supplied with demineralised water and extending inside the exhaust fumes flow chamber, in such a way as to use the heat from the hot fumes coming from the gas turbine unit to generate steam to be supplied to the steam turbine unit; - a heat maintaining assembly for controlling the temperature in the steam unit during the shut-off of the plant; the heat maintaining assembly comprising: ▪ a first supply line (23; 38) configured to supply a first flow rate (Q1; Q2) of heated air into at least one first steam feeding conduit (28; 43) of the steam circuit supplying the at least one first steam turbine (7a; 7b); the first air supply line (23; 38) comprising a first blower (30; 44) and at least one first heater (31; 45); ▪ a first upper casing temperature sensor (26; 41) arranged outside the first upper casing and configured to detect a first upper casing temperature (TU1; TU2); ▪ a first lower casing temperature sensor (25; 40) arranged outside the first lower casing and configured to detect a first lower casing temperature (TL1; TL2); ▪ a control device configured to regulate at least the first blower (30; 44) on the basis of the difference between the first upper casing temperature (TU1; TU2) and the first lower casing temperature (TL1; TL2). ▪ a first supply line (23; 38) configured to supply a first flow rate (Q1; Q2) of heated air into at least one first steam feeding conduit (28; 43) of the steam circuit supplying the at least one first steam turbine (7a; 7b); the first air supply line (23; 38) comprising a first blower (30; 44) and at least one first heater (31; 45); ▪ a first upper casing temperature sensor (26; 41) arranged outside the first upper casing and configured to detect a first upper casing temperature (TU1; TU2); ▪ a first lower casing temperature sensor (25; 40) arranged outside the first lower casing and configured to detect a first lower casing temperature (TL1; TL2); ▪ a control device configured to regulate at least the first blower (30; 44) on the basis of the difference between the first upper casing temperature (TU1; TU2) and the first lower casing temperature (TL1; TL2).