Research On Transformer Differential Protection Of The Baoquan Substation With Inner Bridge Connection

The power transformer is the key equipment of the power system. Its reliableoperation is critical to security and stability in the grid. Configuring comprehensiveand reliable protection of the transformer has been an important task for the protectionworkers. As the core part of the transformer protection, the current differentialprotection of transformer longitudinal been widely applied. Different system wiring,transformer inrush current, and current transformer saturation problem has been animportant factor to affect the correct operation of differential protection. This articleclosely integrate the characteristics of the Baoquan110kV substation and in-depthstudy the inner bridge terminal conditions of parallel operation of transformerdifferential protection of the special problems and solutions.The Baoquan110kV substation is a terminal substation, charged with theimportant task of the region’s industrial and mining enterprises and residentialelectricity. Baoquan110kV substation has two main transformers.110kV bus workswith the Inner Bridge Connection. In this paper, on the base of a detailed analysis ofthe factors of the impact of transformer differential protection of the right action,combined with the110kV bus main electrical wiring the Baoquan substation,transformer load switching is possible and should surge phenomenon, and propose theappropriate measures to resolve.Transformer differential protection is correct action by the saturationcharacteristics of the current transformer, inrush current and sympathetic inrush. InInner Bridge Connection substation, when a transformer load closing, non-periodiccomponent of the surge flow through the system resistance produce non-periodicvoltage to the normal operation of the transformer flux gradually reverse the increase,and ultimately achieve reverse saturation and cause sympathetic inrush. The directionof sympathetic inrush and airdrop transformer magnetizing inrush current is opposite,and biased timeline on the other side, the peak is gradually increasing and thencontinue to decay, and has a longer duration. Sympathetic inrush in a strongnon-periodic component causes the TA transient saturation occurred, causing poorflow, resulting in differential protection malfunction.On the basis of theoretical analysis, the results of the simulation of theoreticalanalysis on PSCAD/EMTDC prove the validity of the analysis, and proposedimprovement measures to solve the problem of sympathetic inrush caused by thedifferential protection malfunction.