| The safety operation of power grid is seriously threatened by atmosphere pollution.So far plenty of studies on insulator pollution flashover performance and its mechanism have been done by worldwide research institutions.It is found by them that insulator top/bottom contamination non-uniformity affects flashover process.Then the correction method for flashover voltage under non-uniform pollution was proposed and applied by engineering practice.Various achievements about insulator contamination and flashover researches help inhibit large scale pollution flashover accidents.Even so,pollution flashover is still happening in certain areas.The crossing paths of our nation's transmission lines are featured with typical microtopography and micrometeorology,making insulator contamination process very complex.As a result,the current contamination model and simulation results can not totally reflect actual conditions.For example,in continental climate and plateau mountain climate areas,transmission lines external insulation will be affected by a long-term period of unidirectional airflow,causing a persistent difference of flow field distribution on insulator windward and leeward sides.This situation will probably cause obvious non-uniform pollution on insulator's windward/leeward side,and thus affect its flashover performance.On the promise that the airflow functions on insulator contamination process with its lateral component,this thesis studied insulator surface pollution deposit,analyzed its pollution distribution on windward/leeward side,and then revealed the dc flashover performances of insulator under windward/leeward non-uniform pollution.Basing on field charging theory,the thesis studied the force bearing properties of pollution particle in typical suspension insulator's surrounding dc electric field,and analyzed the variations of pollution particle moving process and moving speed,through which the effect of dc electric field on insulator contamination was then revealed.With the combination of electric force calculation and fluid dymanic simulation,the thesis analyzed the bearing forces as well as the movement declination of pollution particle on insulator surface,and then obtained the influencing rules of wind speed and particle diameter on insulator surface pollution distribution.Basing on particle collision dynamics,the physical process of collsion,agglomeration and separation among pollution particles was analyzed.The influencing rules of wind velocity,particle diameter,and surface inclination angle on pollution particle's depositing/exiting were also obtained.And then the improved pollution particle accumulation model was proposed.With the overall consideration of electric field,air flow field and pollution particles' accumulating/exiting dynamic process,the numerical simulation of pollution particle depositing on typical suspension insulator surface was carried out.Combining with the experiment results of insulator contamination in circulating-type wind tunnel platform,the proposed pollution particle accumulating model as well as the consideration of dc electric field were verified from three aspects,which are insulator surface contamination situation,pollution mass density,and dc pollution coefficient respectively.According to simulation and experiment results,it is obtained that,with the increment of particle diameter and wind velocity,the effect of electric field on insulator contamination becomes weaker,causing the decrement of dc pollution coefficient.Basing on the verified particle deposit numerical model,the non-uniform pollution performance between insulator windward and leeward sides was systematically studied.The values of windward/leeward side pollution non-uniformity J and leeward side area ratio T under different wind velocity,particle diameter and energized/non-energized conditions were calculated and analyzed.It is found that the lowest J value may reach 1/12,and the increment of wind velocity,particle diameter as well as the dc electric field function will aggravate the pollution non-uniformity.The dynamic predicting method for insulator contamination without precipitations was proposed,and it is found that the errors of the predicted insulator pollution amount and windward/leeward side non-uniformity J were within 20%.Insulator dc flashover performance under windward/leeward side non-uniform pollution was systematically studied.Influencing rules of T and J on insulator string's dc pollution flashover performance were analyzed and obtained.It is found that windward/leeward side non-uniform pollution lowers insulator flashover voltage by 30%.Basing on experimental results,the correction method of insulator flashover voltage under windward/leeward side non-uniform pollution was proposed.On the basis of insulator string dc flashover discharge process obtained by high speed camera,the calculation method for insulator residual pollution layer resistance under windward/leeward side non-uniform pollution was proposed,then the insulator dc flashover dynamic model combing electric field and electric circuit was established and experimentally verified as well.Using this model,the dynamic residual pollution layer resistance and leakage current under different T,J was calculated.It is otained that under windward/leeward side non-uniform pollution,the residual pollution layer resistance during insulator dc flashover can be lowered by 50%,and when close to critical flashover the leakage current rises sharply,causing the decrement of the final flashover voltage. |
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