[en] After a brief review of the methods used to simulate the mains steps, we describe the modifications brought to our DC Converters in order to protect them against the mains fluctuations. It was mostly necessary to avoid the disjunctions due to the excessively sensitive protective and relay systems and to improve the time-response of the electronic drive stages. The second part deals with the description of a 20 KV two cells harmonic filter used to reduce voltage distorsions on the 20 KV GANIL network