Principle of transformer differential protection

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This post was last edited by It will be more tomorrow_bZzMU on 2020-2-15 20:28. The differential protection of a transformer is its primary protection mechanism, and it is implemented based on the principle of circulating current. The so-called differential protection of a transformer refers to a protection mechanism that is based on the comparison of the magnitude and phase of the primary and secondary currents of the transformer. The longitudinal differential protection device is generally used to protect against inter-phase short circuits that occur in transformer windings and leads, as well as single-phase ground short circuits in high-current grounding systems. For internal faults such as inter-turn short circuits in transformer coils, backup protection is usually provided only. The transformer differential protection is based on the principle of circulating current. The principle of transformer longitudinal differential protection requires that, during normal operation as well as in the event of a fault outside the longitudinal differential protection zone (which is the area between current transformers TA1 and TA2), the current flowing into the differential relay be zero, thereby ensuring that the longitudinal differential protection does not activate. However, since the rated currents on the high-voltage side and low-voltage side of the transformer are different, in order to ensure the proper operation of the differential protection, it is necessary to appropriately select the turns ratios of the current transformers on both sides so that the currents remain equal under normal operating conditions as well as in the event of external faults.