Finite Element Simulation Of Dry-type Air-core Power Reactor Temperature Field And Research On Measurement Method Based On Optical Fiber Sensing

Dry-type air-core reactor(hereinafter referred to as DAR)is an important auxiliary equipment in long-distance transmission system,which is mainly responsible for reactive power compensation,limiting short-circuit current,filtering high-order harmonics and reducing harmonic components in DC power system.Compared with the traditional oil immersed iron-core reactor,the failure rate of the DAR is higher.Combining distributed optical fiber sensing technology with transformer equipment such as DAR,reflecting the state of the monitored equipment through the temperature information measured by optical fiber has gradually become a research hotspot.At present,based on the optical fiber sensing technology,it can realize the short-time monitoring of temperature of DAR in the process of high temperature curing.However,there are few studies on the temperature characteristics of DAR under different operating conditions and after turn-to-turn short-circuit fault,and there is a lack of quantitative fault warning mechanism.Based on the numerical simulation method,this paper calculates the electromagnetic field and temperature field of DAR in normal operation and after turn-to-turn short-circuit fault by finite element modeling,and obtains the key temperature monitoring area of DAR in normal operation and the transient temperature change rule after turn-to-turn short-circuit fault,which provides a theoretical basis for DAR temperature monitoring based on optical fiber distributed sensor.Through the ‘magnetic field-circuit’coupling finite element model of DAR,the resistance loss in each layer of winding under rated operation state are obtained,which are substituted into ‘fluid-temperature field’ coupling model as heat source.The axial and radial temperature distribution of DAR under normal state is obtained.Based on this,the finite element models of DAR temperature field under different ambient temperature,airway width,turn number deviation and laying optical fiber are established.The influence of the above factors on hotspot temperature is analyzed,and the key adjustment strategies of distributed optical fiber temperature measurement system under the influence of the above factors are given.By setting short-circuited turn at different radial positions and different axial heights,the transient temperature change law of fault spot after short-circuit is obtained.Based on this,the fault warning time and optical fiber laying mode are proposed.In order to accelerate the measurement speed of DAR temperature monitoring system based on distributed optical fiber sensor,the fast extraction and measurement algorithm of Brillouin Frequency Shift(hereinafter referred to as BFS)are studied.This paper proposed a quadratic polynomial fitting method to extract BFS,and its accuracy and rapidity are verified by the simulation and measured data when the frequency is swept in the range of one linewidth around the peak.In order to improve the accuracy of peak location of Brillouin spectrum,adaptive linear prediction filter is used to denoise the noisy Brillouin spectrum,and then quadratic polynomial fitting is used to extract BFS.The effectiveness of the combined algorithm is demonstrated by simulation and measured data,and compared with the ensemble average algorithm,the superiority of the proposed algorithm in BFS extraction is obtained,which provides a reference for fast temperature measurement along optical fiber based on Brillouin scattering.