METHOD OF THE THREE-PHASE TRANSFORMER AND AUTO-TRANSFORMER DIFFERENTIAL CURRENT PROTECTION Russian patent published in 2018 - IPC H02H7/04 

FIELD: electrical engineering.

SUBSTANCE: field of application: electrical engineering. According to the method, power three-phase transformer each phase each side power circuits currents are transformed in the current transformers, transformer all sides currents are geometrically summed phase by phase, and in case of the any phase resultant current exceeding the established threshold value, disconnecting the power circuits on all sides of the three-phase transformer. In addition, gathering the information about the phase currents from current transformers installed in the substation switchgear transformer cells and located on the sides of high, medium and low voltage, performing matrix description of the currents ratio for transformer with busbars and forming the phase current matrices based on graphs theory and the double recording method, graph vertices are represented by buses, transformer, busbars between the transformer terminals and substation busbars, and arcs are current transformers and circuit breakers branches, respectively, realizing operations over the phase current matrices to obtain the resulting currents, analyzing the resulting currents ratio and, on the basis of the corresponding analysis, checking the transformer differential protection tripping conditions. As the current transformers serviceability checking criterion, the input and output currents sums ratio is used, since each graph arc is reflected with the same weight, corresponding to the current value, in the vertices matrices twice as arc connected to the vertex and directed to it by one vertex matrix, and as arc connected to the vertex and directed away from it by another vertex matrix, then with incorrect values given by the current transformers, the sum of the input and output currents in the two matrices becomes erroneous and does not correspond to the real sum of the circuit currents if the graph both vertices, in which matrices the damaged current transformer measurements are present, are the corresponding protected buses, then the sum of currents for both vertices becomes unequal to zero if one of the graph vertices with the damaged current transformer is hanging, then the sum of the currents for the entire circuit remains zero, in contrast to the case of short circuit in the mains. Detecting the one or two current transformers malfunction, as well as detecting damages on the transformer busbars, producing issue of the control signal when the current transformers faults are detected, realizing the required trips in case of the transformer busbar damages.

EFFECT: technical result is increase in the transformer differential protection method reliability by detecting the current transformers malfunctions, as well as damages to the transformer busbars without impairing the protection speed and use of complex devices.

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