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J. Pontt, J. Rodriguez, J. S. Martin, and R. Aguilera, “Mitigation of Sympathetic Interaction between Power Transformers Fed by Long over Head Lines Caused by Inrush Transient Currents,” Industry Applications Conference,2007, 42nd IAS Annual Meeting, Conference Record of the 2007 IEEE, New Orleans, 23-27 September 2007, pp. 1360-1363, 2007.

has been cited by the following article:

• TITLE: Research on the Reason for Transformer Differential Protection Mal-operation Caused by Sympathetic Inrush

  AUTHORS: Xiangfei Sun, Hongchun Shu, Jianping Zhou

  KEYWORDS: Sympathetic Inrush; CT Transient Saturation; Transformer; Differential Protection

  JOURNAL NAME: Energy and Power Engineering, Vol.5 No.4B, November 13, 2013

  ABSTRACT: The paper is concerned with whether CT transient saturation, which caused by sympathetic inrush, is the direct reason for mal-operation of transformer differential relays. In order to analyze transforming characteristics of saturated CT, the gain of each harmonic current transforming from primary winding to secondary winding of transient saturation CT is calculated. Based on the fact that series sympathetic inrush is easier to lead differential relay mal-operation than parallel sympathetic inrush, the effect of CT saturation on differential relayin the case of both parallel sympathetic inrush and series sympathetic inrush are investigated respectively. Theory analysis and simulation show that higher harmonic will be transferred by saturated CT more easily than lower harmonic, and then the second harmonic proportion of CT secondary side is higher than that of CT primary side. Thus CT transient saturation itself is not essential reason for differential relay mal-operation. Parallel sympathetic inrush and series sympathetic inrush will lead to different location CT saturated. Parallel sympathetic inrush will lead to CT located system side saturated; second harmonic ratio of differential current increase and dead angle is large. Series sympathetic inrush will lead to CT located load side saturated; second harmonic ratio of differential current decrease and dead angle is small.