A method for an improved transformer design for a power plant, comprising the steps of: i) defining at least two critical temperatures (θ hw normal, θ hw contingency, θ h, θ o) in the operation of the transformer, the critical temperatures being selected from at least two of a weighted hotspot temperature for normal load (θ hw normal), a weighted hotspot temperature for contingency load (θ hw contingency), a top liquid temperature (θ o) at maximum load and maximum ambient temperature and a hot spot temperature (θ h) at maximum load and maximum ambient temperature, and determining limits (θ hw,max normal, θ hw,max cotingency, θ h, max, θ o,max) for the critical temperatures, ii) providing a data set of transformer load levels (K, κ) for one or more transformers or for a power plant, wherein the data set comprises the amount of time at a specific load level (K, κ) for a specific ambient temperature (θ a) during the operation of the one or more transformers or the power plant, iii) providing expressions for the critical temperatures in dependence from the transformer load levels (K, κ) and from design parameters (Δθ hr, Δθ or, R, x, y) related to a geometrical and/or an electrical design of a transformer, iv) adjusting the geometrical and electrical design of the transformer and obtaining adjusted values for the design parameters (Δθ hr, Δθ or, R, x, y) such that the critical temperature calculated from at least one of the expressions equals the determined limit, v) after determining an adjusted design, checking if all other ones of the limits (θ hw,max normal, θ hw,max contingency, θh,max, θ o,max) for the critical temperatures (θ hw normal θ hw contingency, θ h, θ o) are observed, and, if this is not the case, iterating the method starting from step iii) and setting the design parameters (Δθ hr, Δθ or, R, x, y) to their adjusted values, comprising the step of producing a transformer having the adjusted values of the design parameters (Δθ hr, Δθ or, R, x, y) and/or using a transformer having the adjusted values of the design parameters (Δθ hr, Δθ or, R, x, y) in the power plant. i) defining at least two critical temperatures (θ hw normal, θ hw contingency, θ h, θ o) in the operation of the transformer, the critical temperatures being selected from at least two of a weighted hotspot temperature for normal load (θ hw normal), a weighted hotspot temperature for contingency load (θ hw contingency), a top liquid temperature (θ o) at maximum load and maximum ambient temperature and a hot spot temperature (θ h) at maximum load and maximum ambient temperature, and determining limits (θ hw,max normal, θ hw,max cotingency, θ h, max, θ o,max) for the critical temperatures, ii) providing a data set of transformer load levels (K, κ) for one or more transformers or for a power plant, wherein the data set comprises the amount of time at a specific load level (K, κ) for a specific ambient temperature (θ a) during the operation of the one or more transformers or the power plant, iii) providing expressions for the critical temperatures in dependence from the transformer load levels (K, κ) and from design parameters (Δθ hr, Δθ or, R, x, y) related to a geometrical and/or an electrical design of a transformer, iv) adjusting the geometrical and electrical design of the transformer and obtaining adjusted values for the design parameters (Δθ hr, Δθ or, R, x, y) such that the critical temperature calculated from at least one of the expressions equals the determined limit, v) after determining an adjusted design, checking if all other ones of the limits (θ hw,max normal, θ hw,max contingency, θh,max, θ o,max) for the critical temperatures (θ hw normal θ hw contingency, θ h, θ o) are observed, and, if this is not the case, iterating the method starting from step iii) and setting the design parameters (Δθ hr, Δθ or, R, x, y) to their adjusted values,