Research On The Key Issues For Protective Relaying Of Ultra-high Voltage Transformer

Ultra-high voltage transformer is the core equipment for ultra-high voltage power transmission.However,UHV transformer has been running under high operating voltage grade,complex structure and special core material.The characteristics present new and special requirements to relay protection.So it is particularly important to futher study the UHV transformer protection.The paper analyzed such aspects as structure, material and so on which is is different from the conventional transformer.The characteristics of UHV transformer have adverse effect on regulating transformer differential protection to avoid unbalance current and the original second harmonic restraint principle for inrush current.The article has carried on research for special question of the UHV transformer relay protection and putting forward the corresponding solutions in detail.Firstly,in the face of the situation that the value and direction of unbalance current changes with UHV transformer taps ragulating.Putting forward by means of regulating winding modify the differential protection of software and hardware, and achieve intelligent compensation for the unbalance current.The method was compared with traditional methods which has great superiority and can greatly simplify the protection setting calculation for UHV transformer.Secondly,the digital simulation model of UHV transformer differential protection was set up for which analyzing the characteristics of inrush current.From simulation it can be got that the distortion of inrush current is serious and second harmonic content is lower than that of conventional.The paper proposed using closing resistor to restrain inrush current and the value of closing resistor was confirmed by inrush current restraining rate. The effectiveness of the method was verified through theoretical calculation and simulation analysis.Finally, according to the simulation analysis of inrush current, putting forward the multiple criteria for inrush current identification.No load closing situation of UHV transformer can be effectively identified.The multiple criteria is effective which was proved by simulation.