Ways of constructing of measuring and starting elements of microprocessor devices of fast acting automatic transfer switch

Abstract

Microprocessor devices of fast-acting automatic transfer switch (FATS) are widely spread in modern net-works to increase the reliability of power supply of industrial plants in case of short-term violations of normal power supply mode. Presence of motor load in such networks requires minimizing the power interruption time to provide more favorable conditions for self-starting of electric motors. However, currently existing operation algorithms of measuring elements of FATS devices are based on the decomposition of the measured signal by using a Fourier integral, and require observation interval equals to the period of the industrial frequency. The known directional elements that are used in microprocessor-based FATS devices do not ensure reliable operation of the device with asymmetric and nearby fault. Therefore, the purpose of the work is to increase the speed of operation of the algorithms of the measuring elements of microprocessor devices of FATS, as well as to increase the reliability of the starting directional element in case of nearby fault and deep voltage drops. To achieve this goal the author uses the method of computer simulation. The method of a full-scale experiment on a laboratory bench to verify the obtained theoretical results is used. The author improves the algorithm to determine the orthogonal components of the measured current and voltage signals by integral averaging of instantaneous discrete values of the measured signals and their derivatives over the observation interval with a duration of less than a half-period of the industrial frequency. The algorithm of the operation of the starting directional element in case of deep voltage drops caused by nearby fault in both the external and internal power supply network has been improved by using the main power supply voltage from the added memory element of the pre-fault measurement cycle as a reference voltage to determine the power direction. The obtained results show that the proposed algorithm for the operation of the measuring elements will make it possible to obtain the value of the phase and amplitude of the measured signal in a time equals to 0,005 s. and use of an improved starting directional element makes it possible to increase its reliability in case of deep voltage drops and asymmetric short circuits. The proposed algorithms of operation of the measuring elements and the starting directional element can be used in FATS devices.