Abstract: The invention concerns a method for purifying the cooling circuit of an alternator stator, characterized in that part of the water of the closed cooling circuit is derived upstream of the alternator towards the deionization circuit supplying the recovery tank, said deionization circuit comprising a mixed bed demineralization circuit and a treament circuit placed parallel to the demineralization circuit, and when the inflow rate into the deionization circuit is fixed at a value less than 10%, preferably less than about 20% of the nominal flow passing through the stator, the treatment circute consists in a cation-exchanging resin; when the inflow rate into the deionization circuit is fixed at a value higher than 10%, preferably higher than about 20% of the nominal flow passing through the stator, either the treatment circuit is interrupted, or the treatment circuit consists of a cation-exchanging resin or a mixed bed resin.