Application Of J-A Model In Transformer Relay Protection

With the construction and operation of ultra-high voltage long-distance transmission lines in China is increasing,more and more large-capacity transformers are also used.In the power system distribution and transmission of each ring,the power transformer is widely used,the accurately work of it will be directly related to the entire power system can be continuous,reliable and stable work.However,relative to the line protection,the correct operation rate of the transformer protection is still low,affecting the operation of the power system.First of all,this paper introduces the background and significance of the paper.This paper analyzes the current method of transformer protection and the problems that may be encountered,and summarizes it as transformer protection scheme based on current quantity,transformer protection scheme based on voltage waveform characteristic,and transformer protection method using current and voltage simultaneously.It is very important to study the internal structure of the transformer to analyze the transformer protection,to analyze the transformer protection based on the current or voltage variable.Then the process of generating and analyzing the process of transformer inrush current is introduced and analyzed.The second harmonic content of single phase transformer and three phase transformer inrush current is studied.It is shown that the second harmonic content will be reduced in the case of severe saturation of the transformer,and the judgment of the second harmonic braking will cause the misjudgment of the transformer protection.For the inrush current,the fault current contains a large amount of second harmonic content,while the inrush current attenuation is very slow,also affect the fault removal time.Based on the example of the second harmonic suppression of the three-phase transformer,the Y-? is transformed into the three-phase transformer.As a result of the influence of the circulation,the differential flow is changed there may be a lower harmonic content of the second harmonic flow,affecting the protection of the decision,it will cause the protection of the malfunction.Therefore,in order to be able to study the transformer protection from the essence of the inrush current and the fault,it is necessary to study the characteristics of the transformer hysteresis loop to better distinguish the inrush current and fault.In this paper,the Jiles-Atherton(J-A)hysteresis model is used to study hysteresis.This paper introduces the basic principle of J-A hysteresis model and its hysteresis mathematical model and the current research status.The differential equation of J-A model is deduced,and the J-A hysteresis model is modeled.The significance of each parameter in the model is analyzed The Finally,genetic algorithm and differential evolution algorithm are used to identify the model parameters,which provides a prerequisite for studying the transformer using J-A model.In this paper,the hysteresis loop is used to analyze the method of guiding the admittance of the transformer.The hysteresis loop is used to explain the meaning of the equivalent model of the support admittance,and the hysteresis loop is used to protect the hysteresis and the algorithm was set.The protection principle is not based on differential protection,not affected by the inrush current.It is verified that the protection algorithm is verified by the simulation.Whether the transformer has the effect of inrush current only affects the charge acceptance of the auxiliary admittance.The conductance of the auxiliary admittance reflects the energy loss inside the transformer and is very sensitive to the inter-turn short circuit fault.Compared with the commonly used second harmonic principle can effectively identify the small turns of the inter-turn short circuit fault,the transformer cast in a slight inter-turn short circuit,etc.,the protection of the tuning method is simple,set the margin,with a high degree sensitivity and reliability.