A method of determining a reduction of remaining service lifetime of an electrical device during a specific time period of operation of said electrical device, said electrical device being connected to a power distribution network, and having a maximum operating voltage and a maximum operating temperature, said method comprising the steps of: providing a measurement system comprising a voltage measurement device, a current measurement device, and a temperature measurement device, measuring a set of voltage values corresponding to the voltage applied to said electrical device by said power distribution network during said specific time period by using said voltage measurement device, measuring a set of current values corresponding to the current applied to said electrical device by said power distribution network during said specific time period by using said current measurement device, deriving a temperature value corresponding to the temperature of said electrical device during said specific time period by using said temperature measurement device, determining a temperature dependent aging factor on the basis of said temperature value, determining said reduction of remaining service life on the basis of said specific time period, and said temperature dependent aging factor, wherein said temperature measurement device is adapted to measure the ambient temperature outside said electrical device and derive said temperature value from said ambient temperature, said set of current values, and said set of voltage values, characterized by determining an amount of harmonic load on said electrical device on the basis of said set of current values, determining a reduced maximum operating temperature of said electrical device on the basis of said amount of harmonic load and said maximum operating temperature, and determining the temperature dependent aging factor on the basis of said temperature value and said reduced maximum operating temperature. said electrical device being connected to a power distribution network, and having a maximum operating voltage and a maximum operating temperature, said method comprising the steps of: providing a measurement system comprising a voltage measurement device, a current measurement device, and a temperature measurement device, measuring a set of voltage values corresponding to the voltage applied to said electrical device by said power distribution network during said specific time period by using said voltage measurement device, measuring a set of current values corresponding to the current applied to said electrical device by said power distribution network during said specific time period by using said current measurement device, deriving a temperature value corresponding to the temperature of said electrical device during said specific time period by using said temperature measurement device, determining a temperature dependent aging factor on the basis of said temperature value, determining said reduction of remaining service life on the basis of said specific time period, and said temperature dependent aging factor, wherein said temperature measurement device is adapted to measure the ambient temperature outside said electrical device and derive said temperature value from said ambient temperature, said set of current values, and said set of voltage values, characterized by determining an amount of harmonic load on said electrical device on the basis of said set of current values, determining a reduced maximum operating temperature of said electrical device on the basis of said amount of harmonic load and said maximum operating temperature, and determining the temperature dependent aging factor on the basis of said temperature value and said reduced maximum operating temperature. providing a measurement system comprising a voltage measurement device, a current measurement device, and a temperature measurement device, measuring a set of voltage values corresponding to the voltage applied to said electrical device by said power distribution network during said specific time period by using said voltage measurement device, measuring a set of current values corresponding to the current applied to said electrical device by said power distribution network during said specific time period by using said current measurement device, deriving a temperature value corresponding to the temperature of said electrical device during said specific time period by using said temperature measurement device, determining a temperature dependent aging factor on the basis of said temperature value, determining said reduction of remaining service life on the basis of said specific time period, and said temperature dependent aging factor, wherein said temperature measurement device is adapted to measure the ambient temperature outside said electrical device and derive said temperature value from said ambient temperature, said set of current values, and said set of voltage values, characterized by determining an amount of harmonic load on said electrical device on the basis of said set of current values, determining a reduced maximum operating temperature of said electrical device on the basis of said amount of harmonic load and said maximum operating temperature, and determining the temperature dependent aging factor on the basis of said temperature value and said reduced maximum operating temperature.