Abstract
The article considers the problem of excessive triggering of a transformer differential protection during external short circuits. The existing restraining algorithms for automatically increasing the protection tripping current during external short circuits are described. It is noted that in the modes with deep saturation of current transformers, none of the restraining algorithms provide reliable performance of the differential protection. It is proposed to apply the phase comparison principle for currents in the protection legs, in addition to restraining, to improve the reliability of the differential protection. A logical scheme of the algorithm and formulas for specifying the conditions of operation of the advanced differential protection has been developed. Testing the proposed restraining algorithm with phase comparison principle on the simulation model in MATLAB Simulink showed that the probability of a false tripping during external short circuits decreases by almost 10 times compared with the known restraining algorithms and is no more than 2% in the most heavy modes. The operation of the algorithm was tested during a short circuit in the protected area, the sensitivity of the differential protection is provided in all modes.
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