Dynamic Simulation on Differential Protection of Ultra-high Voltage Transformer

Ultra-high voltage(UHV)transmission possesses enormous economic benefits and technical superiorities,which is a new subject for China and must be studied emphatically.The paper analyzes the actual structure,parameter and differential protection scheme of UHV transformer which will be used in UHV transmission project under construction in China,and its dynamic simulation experiment system is introduced.Through dynamic simulation experiment results,the sensitivity and reliability of differential protections are studied when kinds of internal faults happen and UHV transformer is no-loaded switched on.The following conclusions are obtained:The main winding's differential protections is sensitive to main winding's internal faults,but can't operate sensibly when the voltage regulating winding or the voltage compensating winding inter-turn faults happen,and the differential protection of the voltage regulating winding and the voltage compensating winding are needed respectively,on the other hand,which can be restrained effectively by second harmonic restraint method when UHV transformer is energized.