Analysis On Spatial Magnetic Field Distribution Of Dry-type Air-core Reactors' Inter-turn Short-circuit Fault

With the advantages of linearity of resistance,simple structure,light weight,easy installation and maintenance,dry-type air-core reactors(DAR)are widely used in the grid reactive power compensation,filtering and current limiting and other occasions.There have been many burn accidents since the DAR are put into operation.A large number of analysis show that most of the reactor burnout accidents are caused by the inter-turn short-circuit fault.Improving the reactor manufacturing level is beneficial to reduce the DAR inter-turn short-circuit fault.In addition,effective fault detection method must be equipped with.However,the existing fault detection method has the disadvantages of low sensitivity or poor reliability.Therefore,it is very important to explore a high sensitivity and reliable fault detection method aiming at the problem of DAR inter-turn short-circuit fault.In order to study an effective DAR inter-turn short-circuit fault detection method,the paper has carried on a series of research based on the law of magnetic field distribution in the DAR.Three crucial issues of DAR were investigated in the dissertation,including the analysis of DAR spatial magnetic field calculation method,the relationship between DAR spatial magnetic field distribution and inter-turn short-circuit fault,and the method to judge DAR inter-turn short-circuit fault by spatial magnetic field distribution.To explore DAR spatial magnetic field calculation method is important to study the change rule of the fault magnetic field.The meaning of spatial magnetic field was defined in this paper.The electrical characteristics and equivalent circuit of DAR were analyzed.Besides,the DAR equivalent model was established according to Kirchhoffs law and Maxwell's equations.Then,a method to calculate DAR inductance and spatial magnetic field was studied based on finite element.The DAR inductance and spatial magnetic field were both calculated through finite element method.The simulation was verified by analytic method.The results show that the built-in reactor model is accurate and the software algorithm is feasible.A parallel DAR applied to 35kV was selected as the inter-turn short-circuit fault model in order to study the magnetic field characteristics of DAR inter-turn short-circuit fault.Different inter-turn short-circuit faults were set in the different positions of the fault model.The different spatial magnetic fields in ATC and LTC under different faults were compared to summarize the law of the magnetic field distribution with fault.The paper presented a method for detecting the DAR inter-turn short-circuit fault based on the variation of DAR spatial magnetic field.The magnitude of the magnetic field change in the observation point,the degree and the relative height of inter-turn short-circuit fault were taken as fitting variables.The fault detection function between fault location or degree and magnetic field was established.The method of judging fault by magnetic field variation was used to verify the effect of fault detection function.The results show that the error between calculate fault and actual fault are within the acceptable range,which proves that the fault function has a good effect on fault detection.