SIMULATION OF TRANSFORMER DIFFERENTIAL PROTECTION IN THE MATLAB ENVIRONMENT

Abstract

Currently, relay protection is based on microprocessor units, which have expanded functionality in comparison with traditional electromechanical means. For the correct operation of these devices, it is necessary to enter the actuation settings, which are calculated manually taking into account the characteristics of a particular power system. Modeling of relay protections in the MatLab environment allows reducing the role of the human factor and minimizing possible errors. (Research purpose) The research purpose is to develop a model of differential relay protection of the transformer in the MatLab Simulink environment. (Materials and methods) The article presents a model of a power system with a power two-winding transformer and differential relay protection with the functions of a current cut-off, differential protection with bias and blocking of the magnetization current surge. (Results and discussion) In the external short-circuit mode, the current protection does not acts, which indicates that the differential protection against external short circuits is detuned. In the short-circuit mode, current cut-off and protection with bias are triggered from the sides of the lower and higher voltages, which also indicates the adequacy of the model. Testing in the magnetization current surge showed that with the 0.15 detuning setpoint recommended by manufacturers of relay protection devices, the protection is blocked for more than 15 seconds, which is unacceptable in practice. The adequate operation of the relay protection is noted at a setpoint of 0.7. The dependence of the harmonic composition of the magnetization current surge on the switching moment on the transformer relative to the transition of the supply voltage through zero was revealed. (Conclusions) The developed model implements the functions of differential protection of the transformer, adequately reproduces all the processes of digital signal processing in microprocessor relay protection units, allows you to check the correctness of functioning in different modes and at different actuation settings.