Torque stress for generators connected to medium voltage distribution systems

The effects of grid faults on large generators in a power system have been widely investigated starting from the ´70s, and proper remedial actions are today known. The diffusion of distributed generation with the deployment of small and medium-size generators connected to the MV distribution network opens new problems not yet investigated into details. Typically, distribution networks experience a high number of faults, mostly involving the ground circuit, and these faults affect the operation of generators and may, in the worst cases, jeopardize their own integrity. The paper analyzes the typical faults on a MV distribution system and their effects on distributed generators. A real and unfortunately rather typical case of repeated generator break-downs due to high torque stress is presented and discussed. In the last part of the paper a possible innovative solution to mitigate this problem is proposed.