This paper present the sympathetic inrush phenomenon analysis and the solution for a Power Transformer. The objectives are to investigate the sympathetic inrush phenomenon and then propose a solution to overcome the unnecessary tripping phenomena due to mal-operation of the relay. When the transformer is close without load, it led to the mal-operation of the protection relay. It occurs because when the transformer is being closed, it will produce excitation current that will pass the system resistance, resulting in saturations that generate a phenomenon called sympathetic inrush current. This phenomenon has been pointed out as one of the reasons for false operation of transformer differential relays. Based on the simulation of the simplified basic network of two parallel 3phase, 100MVA, 132kV/11kV power transformers, the phenomenon and characteristics are analyzed. PSCAD software is used for system execution. The sympathetic current and the inrush magnetizing current reach the peak value alternately, on alternate half cycle which sharing transient current of two transformers is almost symmetrical. As to come out with a solution, two options are being investigated, which are to reduce the 2nd harmonics setting from 20 to 15 and to implement a cross blocking feature to block a tripping when one of the phases experiences higher 2nd harmonics. The simulations show both of the options can solve the problem. By dwelling into the implications, the second option which to implement a cross blocking is accepted since it is safer, cheaper and does not require hassle job to the practitioners to being implemented. Since this cross blocking feature is only incorporated with high- set Transformer Differential, it is proposed that TDR type 7UT613 (Siemens) or SEL587 (Schweitzer) is being used. © 2011 Praise Worthy Prize S.r.l. - All rights reserved.