Dynamic modelling of protective current transformes

ABSTRACT DYNAMIC MODELING OF PROTECTIVE CURRENT TRANSFORMERS TAŞMAZ, Hacı MS. Electrical and Electronics Engineering Supervisor: Assoc. Prof. Dr. Mehmet TÜMAY August 2001, 110 pages Because of its nonlinear core characteristic, it is difficult to analyze current transformer CT performance in any protective scheme under fault conditions. CT core subjected to transient conditions saturates which causes maloperation of protection relays. To overcome this problem, many mathematical models were proposed for the CT cores in the past, which were mostly complex and inaccurate. The aim of this study is to investigate the transient characteristic of a CT under fault conditions. For this reason, a new mathematical model for CT core characteristic was proposed. In addition, a fault current model for a typical power plant was proposed. A 400/1 A current transformer was simulated with various maximum offset fault currents up to 3000 A for different values of burden resistances. A computer program was written using the proposed core model and CT model equations. The simulation results were seen to be accurate and closely fit into the experimental and simulation results proposed previously. inKeywords; Ferromagnetic hysteresis modeling, Fault current modeling, Current transformer modeling, Computer simulation, Graphical analysis, IV