Geomagnetically induced current (GIC) results in the part-cycle saturation of the transformer core and contributes to a considerable increase of the harmonic components in the transformer currents. Under such conditions, transformer differential protection is expected to be blocked from operation, failing to clear internal short-circuit faults. This paper conducts a detailed analysis of the differential protection performance for various fault types under the GIC conditions. An accurate transformer model, validated by the GIC experimental results, is employed in the time-domain simulations within the EMTP-RV program environment. It is revealed that the GIC makes the differential relay incapable of clearing some internal faults. Moreover, it is shown how some factors, such as the fault resistance, the second harmonic inhibition level, and the transformer loading, affect the relay performance in the GIC conditions. The results highlight the need to modify the differential relay logic in order to prevent irreversible damage to the transformers and improve the power system resiliency and reliability during the GIC. Finally, a potential approach for enhancing the differential protection performance under the GIC conditions is proposed.

地磁感应电流（GIC）导致变压器铁芯的部分周期饱和，并导致变压器电流中谐波分量的显着增加。在这种情况下，变压器差动保护将无法运行，无法清除内部短路故障。本文对GIC条件下各种故障类型的差动保护性能进行了详细分析。在EMTP-RV程序环境内的时域仿真中，采用了经GIC实验结果验证的准确的变压器模型。结果表明，GIC使得差动继电器无法清除一些内部故障。此外，还显示了一些因素，例如故障电阻，二次谐波抑制水平，和变压器负载会影响GIC条件下的继电器性能。结果表明，有必要修改差分继电器逻辑，以防止对变压器造成不可逆转的损坏，并在GIC期间提高电力系统的弹性和可靠性。最后，提出了一种在GIC条件下增强差动保护性能的潜在方法。