Amélioration de la protection différentielle numérique des transformateurs de puissance par la détection, la localisation et l’exploitation des courants inverses

Abstract

Power transformer is very important element of any power system. The development of modern power systems has been reflected in the advances in transformer design. This has resulted in a wide variety of transformers with sizes ranging from a few kVA to several hundred MVA. the Unfortunately, power transformers are subjected to faults and abnormal operating conditions which can affect not only the transformer itself but also other equipment connected to transformer. Thus, it is essential to provide sufficient protection for transformers.Nowadays microprocessor-based relays are widely used to protect power equipment. The elements responsible for detecting turn-to-turn faults are the inverse sequence currents. The scope of this work is to develop a modeling methodology to perform simulations for internal faults such as turn-to-turn for step-down power transformer with capacity above 10 MVA An internal fault which shorts only a few turns of a transformer winding creates a small change in a phase current which can be lower than the pickup current value, while at the same time this current in the faulted area can be of a very high magnitude. The inverse-sequence current is the main tool to detect turn-to-turn faults that involve few turns. Sensitivity of the differential protection relay is important as it prevents evolution into more severe faults, thus reducing time and cost of transformer repair. Simulation is effectuated for various values of sc impedances and it gave satisfactory results.