Current Transformer And Its Application In Differential Protection

Current transformers are widely used in power systems.They are the key link for connecting primary and secondary equipment of power networks,and have a direct and important impact on the stable and safe operation of power systems.The saturation problem of current transformers is a major test for the safety of relay protection.When the iron core is saturated,the current is distorted,and the secondary side protection device cannot correctly obtain the power system operation information.The current transformer transient process is complex and is affected by many factors.When a fault occurs,the saturation phenomenon is likely to cause the relay protection to be mis-moved or rejected.Therefore,the anti-saturation measures and the fault information before saturation and the saturated current waveform are used to intelligently identify the operating state of the power system to ensure relay.It is very important that the protection device can operate normally.In this paper,the composition and principle of the current transformer core are firstly studied.The steady state and transient characteristics of the current transformer are analyzed by mathematical model.The transient saturation characteristics of the core are analyzed.In order to solve the problem of non-physical understanding of the hysteresis loop in the J-A theory,the dynamic loss and the static loss are improved.Compared with the improved J-A model,the saturation characteristics and transient characteristics of the core can be better reflected.The speed of the solution is improved by the Runge-Kutta method,and the superiority of the improved model is verified by simulation.The UMEC transformer model is built to verify the necessity of saturation characteristics research.Based on this,a simulation model based on J-A theory is built to analyze the influence of various factors on the secondary side current waveform.By establishing a simulation model of current transformer,the steady-state saturation characteristics and transient saturation characteristics are analyzed,and the waveform of current malformation and the adverse effects on relay protection are analyzed according to the specific conditions.Then,the simulation model of the power system is established,and the current waveform of the secondary side under different conditions is analyzed.The influence of distortion waveform on the power system is analyzed,and anti-saturation measures are proposed.Through the secondary side current waveform data of the current transformer under different parameters,a random forest model is established to identify different types of faults and achieve good results.Through the research in this paper,the differential protection model and the random forest model are combined.The random forest model can identify the secondary current waveform after saturation of different parameters of the current transformer within a certain range,and determine the fault type.Through simulation verification,the random forest model can extract the effective information in the current waveform in the power system relay protection,can identify different types of faults 100%,and can intelligently identify the waveform before and after the current transformer saturation,thus confirming the fault.Type has important practical value for the safe and stable operation of the power system.Figur [39] table [3] reference [67]...