Specific features of the development of differential-phase transformer protection systems on the basis of magnetic reed switches

Characterizing a sustained short-circuit current with the use of reed relays

“…where k 0 is the coefficient ensuring that the current from only a single phase acts on the MOC (e.g., k 0 = -/2π for phase A [8]), γ 1 (γ 2 ) is the angle between the longitudinal MOC axis and vec tor H A (H B ) of the magnetic field produced at point M by the current in phase A (B), l A and l B are the shortest distances from point M to the centers of cross sections of the phase current leads, (I ac.c ) and H r.c (I r.c ) are the actuation and reversion magnetic strength (current) values corresponding to the closing and opening of the contacts of an MOC positioned at the center of the coil of a standard solenoid in such a way that their longitudinal axes are aligned, and w c and l c are the number of turns in the coil and the coil length (l c ӷ r c , where r c is the coil radius). It is assumed in (3) that…”

“…The second formulas in (4) hold true if the magnetic fluxes near the phase current leads and in the coil are exactly the same and in the absence of mounting errors. They were used already in [4,8], and the I ac determination errors did not exceed 6%.…”

“…At present, it is not possible to decide between the options available because the majority of the studies are still ongoing. Relay protection based on magnetically operated con tacts (MOCs, reed relays) [4][5][6][7][8] is widely used in engi neering [9,10] and holds promise for future use [10,11]. Certain advantages (which are significant for RP purposes) of MOCs over other magnetosensitive ele ments are detailed in [6][7][8].…”

“…Relay protection based on magnetically operated con tacts (MOCs, reed relays) [4][5][6][7][8] is widely used in engi neering [9,10] and holds promise for future use [10,11]. Certain advantages (which are significant for RP purposes) of MOCs over other magnetosensitive ele ments are detailed in [6][7][8]. However, further imple mentation of MOC based RP is held back by a lack of techniques for characterizing the short circuit (SC) current curve, the analysis of which forms the basis of various software protections, using MOCs.…”