Development of the error reducing method for the determination of the alternating current amplitude without the use of current transformers

Abstract

The object of the research is methods of current amplitude identification without using current transformers. Most solutions are built on reed switches, which have a limitation of the operation speed due to the mechanical nature of the reed contacts. Therefore, the time duration is a random variable with a significant variation. Thus, the problem that needs to be solved is the reduction of the error of current amplitude identification associated with the mechanical properties of contacts. According to the conducted literature analysis, the presence of contact bounce of reed switches increases the errors of sinusoidal current amplitude identification approximately up to 8–10 %. The mathematical modeling allowed us to investigate this phenomenon and research its influence on the method. The suggested model was then approved via in-situ modeling. Consequently, to reduce the errors of measuring the current amplitude via a reed switch, the replacement with an analog or discrete Hall sensor was proposed. A mathematical model of the discrete Hall sensor operation and a method for identifying the amplitude of the alternating current were developed. During the experiment, it was found that the analog Hall sensor has a limitation in measuring currents of large rates, at which the discrete sensor worked stably. Hence, the last was chosen. It is worth noting that the study of the behavior of the Hall sensor was limited to the value of the alternating current amplitude, four times the opening current with an average error of less than 3 %. The method suitable for discrete Hall sensors simplifies and reduces the cost of the measuring instrument design. However, the practical implementation of the suggested method requires also the application of devices concentrating the magnetic field on the Hall sensor surface