Patent ID: 8765477

Claim:
Method for establishing hot spot temperature T PC * of oil contained in an electric apparatus, according to different operating conditions of the apparatus, the method comprising: a) operating the electric apparatus according to at least one predetermined operating condition in order to increase temperature T H of the oil, the oil comprising at least one chemical compound soluble in the oil, each compound forming in a irreversible way a residue soluble in the oil at a residue transition temperature T R ; b) taking at least one sample of oil during or after step a) while measuring the oil temperature T H ; c) performing an analysis of the at least one sample taken in step b) in order to determine whether or not the residue is present; d) from the analysis of the step c), evaluating a hot spot temperature T PC under the at least one predetermined operating condition having allowed the presence of said at least residue in the sample, as being equivalent to the residue transition temperature T R of said at least one residue; e) calculating a difference ΔT between the hot spot temperature T PC and the oil temperature T H under the at least one predetermined operating condition; and f) establishing that the hot spot temperature T PC * according to any other operating condition of the apparatus is obtained according to the following equation: T PC *=T H *+ΔT; T H * being the temperature of the oil under said other operating condition.