Study Of Transformer Differential Protection Based On PowerPC

To improve various problems existing in transformer differential protection device, we have studied the total design scheme of device and the principle of transformer differential protection and inrush distinguishing and TA saturation distinguishing.First, we have applied new technique in the restrain current of the transformer differential protection. We translate any sides of differential to two sides of differential to increase sensitivity of internal faulty. We have applied new three lines of percentage bias restraint. It enables the device to gain immunity from TA saturation furthest. It enables unbalance current decrease to smallest that we have applied self-adjusting compensation method.Second, we have studied distinguish method of inrush current. Differential protection of second harmonic restraint might operate in error caused by external faulty if power system connects with long wire. The principle of the waveform symmetry can make up the shortage about trip with long delay of the principle of the second harmonic current restraint because it uses"OR"block mode. The newer principle of fuzzy distinguish enable relay has higher reliability and greater redundancy.Third, we have studied distinguish method of TA saturation. The shortage of principle of the harmonic restraint is that the third harmonic current might to follows the transformer internal fault. The principle of the time difference can rightly distinguish the TA saturation. However, the setting of time difference is a difficulty. The principle of the additional restraint region can rightly distinguish the TA saturation also. The principle'shortage is that its speed might to be slow due to some reasons. The TA saturation comprehensive criterion has higher reliability and rapidness. And the criterion can identify the transformer's conversion fault rapidly while differential protection is blocked.Finally, the feasibility of percentage bias restraint of transformer differential protection and distinguish restraint method of inrush current and distinguish method of TA saturation are validated by dynamic simulation.