Study On DC Corona Performance Of Ice-covered Wire Based On Corona Cage Experiments

The transmission lines in China are faced with various degree of icing problem;icing could worsen the corona effect of transmission lines dramatically even in the range of designed icing thickness.At present,some researches have been carried out in the field of AC corona performance of ice-covered conductors,but there is still a large blank for the case of DC ice-covered conductors.To obtain the DC corona loss data of ice-covered conductors suitable for the electric power design practice in China,and to deal with the audible noise problem caused by the constantly increasing voltage level of China's DC transmission lines,it is of great academic significance and engineering value to study the DC corona performance of ice-covered conductors.In this dissertation,corona performance experiment platforms based on corona cage are designed and constructed in labratorary and XUE FENG MOUTAIN wild icing observation station.The influence of voltage polarity,freezing water conductivity,icing electric field intensity and icing severity on the icing morphology,corona loss and audible noise characteristics of rime and glaze ice-covered wire are studied.Besides,the generation mechanism of audible noise of ice-covered wire are also corrected.In laboratory,the influence of voltage polarity,freezing water conductivity,icing electric field intensity and icing severity on the icing morphology and corresponding corona loss are studied.The relationship between corona loss and nominal electric field intensity of rime and glaze ice-covered wire is a power function.The glaze icing process of wire has remarkable polarity effect.In the electric field intensity range concerned by extra-high and ultra-high voltage transmission lines,the corona loss of glaze ice-covered wire is the largest,followed by that of rain weather,and the corona loss of rime ice-covered wire is the smallest.With higher freezing water conductivity,lower icing electric field intensity or severer icing severity,the corresponding corona loss of the ice-covered wire is higher,and the corona onset voltage is lower.Among them,the factors that have the greatest influence on the corona loss of rime and glaze ice-covered wires are the icing electric field intensity and the freezing water conductivity,respectively.An improved corona loss method is proposed to decide the corona inception voltage of ice-covered wire,the resulted surface irregularity coefficients of rime and glaze ice-covered wires are in the range of 0.325?0.447 and 0.172?0.307,respectively.The influence of voltage polarity,freezing water conductivity,icing electric field intensity and icing severity on the audible noise of ice-covered wire are studied in this dissertation.The L₅₀ of audible noise and the nominal electric field intensity of the rime and glaze ice-covered wires obey the empirical formulas of the deformation form of the inverse proportional function and the logarithmic function,respectively.Icing is the worst case of audible noise for DC transmission lines,and the audible noise of ice-covered is5.0?16.2 d B(A)higher than that of fair weather condition.With higher freezing water conductivity,lower icing electric field intensity or severer icing severity(except for glaze ice-covered wire),the corresponding audible noise of the rime and glaze ice-covered wire are higher,the influence of icing severity is the biggest among them.Base on the correlation between L₅₀ of audible noise and its high frequency components,the environmental noise intrusion problem during long-term automatic measurement process are solved,with a maximum error of 6.2%.Natural icing experiments are conducted in semi-free acoustic field;the results of corona loss and audible noise are compared with that of laboratory results.Only the low frequency components of audible noise are affected in laboratory,the results of corona loss and L₅₀ of audible noise are still applicable to the semi-free field natural icing experiment.The DC corona audible noise of ice-covered wire obeys the normal distribution,and its position parameter is the L₅₀ of audible noise.A sound source model for DC audible noise of ice-covered wire is established based on the experiment results and acoustic theories,and the acoustical power is introduced.The power function relationship between the acoustical power and the nominal electric field intensity of ice-covered is proposed.With the increase of applied voltage,the corona discharge modes of the positive polarity ice-covered wire are studied,and they are the feeble discharge mode,positive burst corona mode,and positive onset streamer mode,respectively.The relationship between the acoustical power and corona loss is segmental linear function,and the slope is increased with the development of corona mode.In addition to the high-speed motion of electrons,the directional movement of ions is also a source of the DC audible noise of ice-covered wires.The audible noise of positive polarity conductor is the main source of DC transmission lines is due to the fact that the ratio of audible noise acoustical power to the total energy released by corona discharge is of three orders of magnitude higher than that of negative polarity wires.