The connection of Distributed Generation at the distribution level has an impact on the protection system. Thus, there is a limitation on the penetration of generation into the network. The protection systems have to be rethought to allow the integration of high Distributed Generation capacity.

The problems in the protection system of a distribution network that may happen due to high penetration of generation into the network were detected and theoretically analyzed. The problems detected were the interruption of the operation of feeder overcurrent protection, the unnecessary trip a healthy feeder, the failure of auto-reclosing and out of synchronism connection including islanding situation. These problems are influenced by the Distributed Generation capacity, its technology and location in the distribution network. The location of the fault also influences these problems.

Through analytical validation it was shown how sympathetic tripping of a Medium Voltage protection scheme might occur when there is high penetration of generation. The results showed that a healthy feeder could become unnecessarily out of service due to the contribution of the Distributed Generation to the fault in an adjacent feeder.

An adaptive protection scheme was presented as a potential solution to integrate high Distributed Generation capacity into the distribution network and avoid sympathetic tripping from happening. Together with the characteristics of a multifunctional relay, this protection scheme automatically alters the operating parameters of the protective relays to maintain optimal performance in response to changing network conditions. This adaptive protection scheme requires an intelligent system, the Smart Substation Controller. This system determines if with the actual state of the network, the change of the operating parameters of the protective relays is necessary. Depending on its mode of operation, this intelligent system can be responsible to send a remote control to the protective relays to change their protection setting group. This approach of adaptive protection can benefit from low latency due to a local control. The intelligent system has interaction with the SCADA/DMS which is the one that states of its mode of operation.

A real time closed loop test to validate the performance of a commercial protective relay under the concept of the Smart Substation Controller was made. For the first test the SSC was not considered. This test allowed to verify that with the existing settings of the phase overcurrent protection function sympathetic tripping may happen due to high penetration of generation into the network under study. For the second test, the SSC was considered. In this case, it was possible to verify the change of the protection scheme into a commercial relay, by an external command, to a more suited protection scheme taking into account the actual conditions of the network, namely the integration of Distributed Generation. In this case it was proved the change of setting group to one in which the operating parameters are better suited to integrate generation into the network and prevent sympathetic tripping from happening. Thus, the change of setting group allowed the Distributed Generation to maintain connected to the network when a fault in an adjacent feeder occurs.

The closed loop test was essential in order to validate the change of setting group in a real application proving the adaptability of the commercial protective relay. This characteristic is appropriate to the Smart Grid context in future Distribution Network in which a large number of Distributed Generation is expected.