变压器三角形侧零序环流助增对差动保护的影响

以Y0，d接线的变压器Y0侧空载合闸的暂态过程为例，分析了三角形（△）侧环流助增对￥0侧相电流的影响，并在此基础上研究了涌流助增对2种不同转角变换方法变压器差动保护的影响。分析结果表明：由于△侧环流的影响，从躲空载合闸涌流的角度分析，基于Y0侧相电流差（iA-iB）的差动转角方式二次谐波含量损失不会很大；而基于Y0侧消零序电流（iA-iB）原理的转角方式可能在某些空投情况下差流某一相的二次谐波特征消失，出现某一相差动电流与内部故障相类似的波形特征，该相二次谐波无法制动引起差动保护动作，同时进一步分析发现，涌流中的3次谐波含量在此情况下是增强的，可以引入3次谐波辅助判据来解决在这种情况下的缺陷。

Influence of Add-assist Circulation Current at Delta Side on Y/Delta Transformer Differential Protection

In recent years, some new phenomena have been observed when recording data waveforms, which lead differential protection mal-operations. It has been discovered that one phase of inrush current in differential calculating current is similar to the internal fault current, and the value of its second harmonic component is almost equal to zero, which is very small and low that could cause transformer differential relay mal-operation. In this paper, the causes of this kind of mal-operations are analyzed. It is pointed out that the strategy of angle compensation in differential protection has a great influence on mal-operations. When energizing an unload transformer on Y0 side, the circulating current in delta side may eliminate or distort inrush current waveforms on Y0 side. This kind of phenomenon in inrush current is called the affection of add-assist (AA) current in inrush. This paper also studies how AA current affects the performance of differential protection with two different current compensation strategies. The results show that symmetric inrush current will occur on Y0 side because of AA current on delta side. Compared to the minus-zero-sequence-current compensation method (iA-i0) , the second harmonic component in differential current only decreases slightly when using the phase-phase compensation method (iA-iB) since the former may cause mal-operations in differential protection because of the vast decrease of the 2nd harmonic component. The current compensation strategy with minus-zero-sequence-current compensation method has been used to some extent in power system widely. It is suggested that the scheme of minus-zero-sequence-current compensation method should not be used in transformer differential protection when applying the 2nd harmonic restrained principle. And the best way is to use the phase-phase compensation method in the case of mal-operations caused by energizing inrush if using the 2nd harmonic restrained method.