Reed Switches Differential Protection of Conversion Facilities with the Second-harmonic Lockout

Advantages and disadvantages of traditional differential protections of conversion facilities and reed switch protections are discussed. A reed switch differential protection is suggested, the sensitivity of which is ensured by the second-harmonic lockout in the case of a magnetizing inrush of the conversion facility transformer. Another difference is that to obtain information about the current in the phases from the high voltage side of the transformer, windings of reed switches mounted near their current conductors are used. A technique for selecting trip set points of such protections is described and the sensitivity of its is estimated. Special attention is paid to the choice of parameters of reed switches mounted near the DC busbar and their windings. Behavior of the protection is considered under different operating modes of the conversion facility, and the field of its use is determined.