Majority Voting Schemes of Differential Protections without Current Transformers with Functional Diagnostics for Converting Units and Electric Motors

Abstract

It is stated that the issue of building up protection relays without CTs is relevant. The solution to this issue using reed switches is proposed. It is noted that the differential protection of converting units and the phase-comparison protection of reed switch-based motors without CTs have low dependability and security in the event of any faulty element. Herewith, the lack of functional diagnostics does not allow determining the faulty element. The authors propose two new protection schemes based on the majority voting principle - the faulty electrical unit trip signal is generated if at least two of the three mutually redundant sets send alarms, which leads to an improvement in both the dependability and security. The operation of the functional diagnostic units, based on the time-pulse principle, is considered. It is shown that the functional check of conductors will allow avoiding the protection malfunction in case of their failure.