Transformer Differential Protection

This article presents the development and implementation of a transformer differential protection scheme that combines simulation, assembly and test with a test case, to finally validate the assembly in a laboratory test with a transformer.The concept of differential protection and the different alternatives that exist for current differential schemes are introduced. A simulation is performed in the DIgSILENT® software on the IEEE 9-Bus System taking the 200 MVA transformer as the element to be protected, where the objective is to simulate internal and external faults to the indicated transformer, obtaining as results; operation times and fault currents in the SIEMENS 7SJ85 overcurrent relays. Subsequently, the differential protection scheme based on percentage relays will be implemented in the overcurrent devices by means of the DIGSI® 5 software, this will be done through the creation of function charts CFC (Continuous Function Chart) and the communication of the IED’s by means of GOOSE messaging (IEC 61850), then the effectiveness of this scheme will be evaluated by injecting fault currents through the CMC 356 test case. Finally, the differential protection scheme will be validated in the electrical protection laboratory of the Universidad Politécnica Salesiana - Sede Cuenca, using a 3.5 kVA three-phase transformer, where internal transformer faults will be simulated to validate the effectiveness and functionality of overcurrent relays in differential configuration.