June 2011
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19 Reads
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3 Citations
The mal-operation of the transformer differential protection occasionally takes place after external fault being removed. At present, the mal-operation is prevented by means of changing the acting area and braking area of differential protection, which adversely affects the clear of transitional fault. This paper analyses the differential current harmonic component by simulation, a new algorithm is proposed according to the features that the triple frequency harmonic is greater than the second harmonic in the period of the mal-operation. The new algorithm is based on the differential protection of the second harmonic braking, and the new braking criterion is presented using the rate of the second harmonic and the triple frequency harmonic in the fundamental harmonic. Simulation results show that the new algorithm is simple and effective, can avoid the mal-operation, and clear transformer transitional fault quickly.