Abstract
To increase the reliability of microprocessor protections, they should be duplicated on the majorization principle. In addition, three duplicate protection systems should have different principles of operation and execution, and two of them could operate without current transformers. We suggest a common protection for all connections in quadrangle switchgear schemes based on the control of current and power direction in the circuits of their connection and is made from electromechanical elements. The current in each phase is controlled by a reed switch mounted near the busbars of these circuits; the reed switch simultaneously functions as a current transformer and a current relay. The current circuits of the two-way power direction relays (PDR) are connected to the reed switch winding, where the EMF is induced by the current in a corresponding phase, and the voltage relays are connected as usual. The sensitivity of the reed switches is considered. The behavior of PDR and reed switches is analyzed in different modes. The conditions for protection operation for closing each connection are derived. The algorithm of protection operation is written as a function of the Boolean algebra. Examples of protection implementation on the basis of electromechanical and semiconductor elements are given. The device diagram is considered.