Investigation of Processes in the Measuring Part of Digital Devices of Relay Protection in the MATLAB Software Package

It was revealed that one of the main reasons for erroneous operation of relay protection devices (RPs) is it being set in a way that does not correspond with the real operating conditions, which in turn is determined by the design procedures of the RP settings. An analysis of modern methodologies of RP adjustment revealed that there are no significant changes as compared with the guidelines of the past decades and, accordingly, there are the same disadvantages. The development of new adjustment techniques using detailed mathematical models taking into account the features of specific RPs and the processes in the measuring converters are considered in the work. Within the framework of solving this problem, mathematical models of measuring part of digital relay protection for various types of intermediate current transformers (ICTs) (active and passive) and filters (of Butterworth and Chebyshev types) are synthesized and a comparative analysis is done of their influence on the output signal waveform in the MATLAB software package, including taking into account the magnetization of measuring current transformers. It is revealed that the simplest (explicit and implicit Euler methods) numerical methods are not suitable to solving the created mathematical models. A comparative analysis of calculation results by these methods and by the more advanced Runge–Kutta method is conducted. The presented theoretical and practical studies made it possible to reliably formulate the requirements for detailed mathematical models of RPs.