Study On The Growth Characteristic Of Icing And The Model For Predicting Thickness Of Rime Accretion On Insulators

As a natural phenomenon, ice accretion on transmission lines has a seriousthreaten on the safe running of grid. So many research institutions have carried out alarge number of researches on ice growth process and its influencing factors ofconductors. Further more, many models and empirical formulas for predicting ice onconductors have been proposed. While, the researches on ice mechanism of insulatorare rare and we have yet to see the reports of insulator icing growth model or relevanttest results. This leads people can’t realize the ice storm warning for the transmissionline insulators and then as far as possible to avoid the accidents of icing flashover. Sothis paper will study the growth performance of icing and propose a model forpredicting thickness of rime accretion on insulators. The researches have somescientific significances and engineering practical values to reveal insulator icingmechanism and promote the realization of ice storm warning system for insulators.Through artificial icing test, the icing growth processes of different typeinsulator were studied and the influences of environmental parameters on icinggrowth of insulator were analyzed. It is found that: the ice on different typeinsulator is different and the icing growth of insulator is non-linear; the lower thetemperature and the larger the wind speed, the larger the amount of ice on insulator;the temperature may affect the ice type; the impact of MVD (Medium VolumeDiameter, MVD) on icing of insulator is not significant for wet growth.Through solve the3-D RANS (Reynolds Averaged Navier Stokes, RANS)equations of airflow and governing equations of discrete droplets, the numericalsimulation of the flow field and droplet trajectories around composite andaerodynamic insulator was carried out. Based on the analysis of the difference offlow field for different type insulator and the influence of icicles on flow field anddroplet trajectories, the difference of ice accreted on different type insulator wasanalyzed from the perspective of fluid mechanics.According to the flow field and droplet trajectories obtained throughnumerical simulation, the droplet collision coefficients on different regions ofpolymeric and aerodynamic insulator were calculated. Meanwhile, the influences ofwind speed and MVD on droplet collision coefficients are analyzed. It is found thatthe collision coefficient increases with the increase of wind velocity and MVD. After the calculation of droplet collision coefficients of insulators, according tothe principle of mass conservation and energy conservation, the model for predictingthickness of rime accretion on composite and aerodynamic insulators has been builtand verified by artificial icing growth test. It is found that when the thickness of rimeon sheds is less than8mm, this predicting model has a good accuracy and the relativeerror is less than8%. When the thickness of rime on sheds is in the range of10~15mm,the accuracy of this model become slightly worse and the relative error is in the rangeof12%~15%.