Determination of the magnitude of short-circuit surge current for the construction of relay protection on reed switches and microprocessors

Abstract

A study of the functioning of reed switches under the influence of a magnetic field created by a current in a conductor in a transient mode with the presence of an aperiodic component has been carried out. A well-known method for determining current using reed switches was implemented. At the same time, it was determined that the originally formulated method did not give the required result within the limits of errors. This is most likely due to the peculiarities of the mechanism of movement of the reed switch contacts. Alternatively, the measurements were taken to take the return currents instead of the pick-up currents and the time between the return times. They are more stable. Simulation is performed, experimental determination of the value of surge current by measuring time is carried out. The main element of the created installation was the power transformer coil with low active and high inductive resistance. As part of the study, the reed switches were placed in a magnetic field with an aperiodic component, as in the transient mode. This study will show the applicability of reed switches for the construction of relay protection devices that will not need current transformers to obtain information about the primary current in the conductor. In the course of the research, it was found that the error in determining the magnitude of current was no more than 10 %. Using microprocessors, it is possible to build relay protection devices with a speed of up to 20 ms. This result makes it possible to build new devices. Since in the well-known developments, it was only said about determining the magnitude of current in a steady state. When building relay protection devices on reed switches, without using current transformers, it will be possible to build backup protections that duplicate not only the devices themselves, but also the primary measuring transformers with other sensitive elements. This will improve the reliability of the power supply.

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

“…4). The previous works [2][3][4] demonstrated only the results of the work without research of the mechanical contacts behavior. The developed mathematical model ( 14) makes it possible to investigate the behavior of the reed contacts (Fig.…”

“…But there were unresolved issues related to susceptibility to external influences. The paper [4] demonstrates a system based on four reed switches and a microprocessor that uses reverse current measurements instead of tripping currents to eliminate errors. This system allows the determination of the short-circuit current with an error of ≤15 % and a response time of 0.02 s. A similar short-circuit monitoring system for distribution systems with distributed generators based on reed switches is shown in [5].…”

Determination of the speed of a microprocessor relay protection device of open architecture with a reed switch and the industrial internet of things

“…1 has a simpler structure, computation and decision-making processes. However, the solutions [4][5][6] as well as [7][8][9]12] consider the efficiency only by end parameters, not covering the problems in providing the requirements of relay protection. Consequently, the considered solutions only have reliable results under certain laboratory or simulation conditions.…”

“…Knowing this parameter, the magnetic sensor is placed at the necessary distance, and the reed switch's trip current I t and return current I r are determined. Thus, using the values obtained and applying (5), we can determine the current amplitude by the formula [12]:…”

“…However, there is still a need for research to say definitively about the advantages and disadvantages. A solution that considers these cases is the use of reed switches to build a device for measuring current [12]. Moreover, the principle of operation is based on the determination of the time of the contact in the closed state, based on which the current is calculated.…”