Stator Single Phase Ground Fault Protection Of Powerformer Based On Grading Insulation

Under the background of the adjustment of energy pattern and the strengthening of resource and environment constraints,the birth of Powerformer has become an important change in energy and power technology,breaking through the limitation of insulation and traditional boost transmission mode,and realizing direct connection between generation units and high-voltage transmission network.However,generator fault protection has long been a bottleneck problem in the field of relay protection technology for main equipment of power system.Especially for Powerformer,whose stator materials,winding mode and grid-connected mode have undergone breakthrough changes,their fault protection strategies must follow the complex fault information given by the inherent attributes of Powerformer,besides the commonness of conventional generator positioning.It has unique physical structure characteristics and presents unique fault mechanism.For this reason,based on the electrical and physical characteristics of Powerformer,considering the hierarchical insulation technology of Powerformer stator windings,this project carries out the research on single-phase grounding fault protection of Powerformer stator,in order to improve the reliability and sensitivity of the protection scheme.Following the following main research contents,this paper carries out the research on single-phase grounding fault protection principle of Powerformer stator based on hierarchical insulation.Firstly,considering the hierarchical insulation technology of cross-linked polyethylene stator winding of Powerformer,the distribution of tooth width at each position of Powerformer stator teeth is given quantitatively.According to the distribution characteristics of magnetic density at different tooth sizes of Powerformer,the qualitative analysis is made.The difference distribution between stator tooth width and EMF of each branch turn of Powerformer is analyzed.Secondly,in view of the interference of third harmonic voltage fluctuation in high voltage transmission network on protection scheme,an adaptive threshold criterion is added to the original protection scheme,and a single-phase grounding fault protection scheme for Powerformer stator based on hierarchical insulation is proposed.Finally,the proposed protection scheme is verified by simulation,and the feasibility of the protection scheme under different fault location and transition resistance conditions is studied.The proposed protection scheme takes full account of the impact of hierarchical insulation technology on the protection scheme of Powerformer stator windings.The simulation results also show that the scheme has obvious advantages in both reliability and sensitivity.It is expected to improve the performance of stator single-phase grounding fault protection of Powerformer in practical application.