Protection system for limiting the impact of the disruptions of an external electrical network on the local network of a site connected to the external network

Protection system for limiting the impact of the disruptions of an external urban or industrial electrical network (3) on a local electrical network (1) of a site which is connected to the external network (3) and which comprises at least one local electric power source, referred to as “local source (6)” connected to the local network (1) and capable of injecting the surplus electric power not consumed by the local network 1 into the external network (3), with the protection system comprising a synchronous machine (9) connected to the local network (1) which is itself connected to the external network (3) by means of a choke (10), referred to as “network choke” which is connected directly to the local network (1), wherein the synchronous machine (9) is a machine with low direct subtransient reactance which is less than 10% of the nominal reactance of the local network (1) and that the protection system comprises at least one auxiliary local choke (13) which is associated with the local source (6) and for which the value of the reactance (L13) is 25 to 40% of the nominal reactance (L6) in PU (Per Unit) of the local source (6) and which is connected to the local network (1) between the above local source (6) and the synchronous machine (9).