Study On The The AC Flashover Performance Of Transmission Line Insulator In Fog Environment

With the development of China’s economy, atmospheric environment isdeteriorating, the fog occurred frequently in China. This is a serious threat to the safetyand stable operation of the power system. The physical and chemical characteristics offog have important influence for the insulator flashover voltage. However, researchersaround the world have carried out little study for it. The author carried out a largenumber of investigations on insulator flashover mechanism through artificial pollutiontests based on previous research results and the existing problems. This paper mainlyfocused on the physical and chemical characteristics of fog, the humidify process ofinsulator surface, the influenced of insulator flashover voltage by the temperature andconductivity of fog-water. And the authors have carried out a large number ofinvestigations on insulator flashover progress in nature fog. With the combination oftheory and experiment, the main conclusions are followed:(1)The humidify process of insulator surface in nature fog are include condensationprocess and droplet colliding process. The condensation process is metastable statesteam changing into steady state water initiatively. The collision characteristics ofdroplet is influenced by fog-droplet diameter and wind speed. And it is increase with thefog-droplet diameter and wind speed increased. In steam fog, the insulator surfacewetting process is mainly condensation effect; In ultrasonic cold fog, the insulatorsurface wetting process is mainly affected by the mist droplets collision on the surfaceof the insulator.(2)The relationship between the flashover voltage of a clean XP-160insulatorstring of1unit and fog conductivity is deduced by least squares and Excel program. Itindicates that the relationship between them could be expressed asU50K a20. TheK and a are134.65and0.158with R2>0.97. The significance and verification test haveturned out the calculating results of the equation (U50K a20) agrees well with thetest result.(3)The relationship between the flashover voltage of an artificially pollutedXP-160insulator string of3units and fog conductivity γ20is deduced by definitionaddition salt deposit density. It indicates that the relationship between them could beexpressed asU50A S a. The is addition salt deposit density，mg/cm2. Itindicates that the relationship between them could be expressed as b20c. The significance and verification test have turned out the calculating results of the equation(U50A S a) agrees well with the test resultf.(4)The flashover voltage of an artificially polluted insulator could be decrease withthe fog temperature increased. The solubility will be increased and the viscosity will bedecreased with the fog temperature increased. And it could dissolve more NaCl and theions in solution could move more quickly.(5)The shape of insulator arc discharge is influenced by wind current. The impactfactor is very small with the wind speed in0~5m. And it is big with the wind speed in10~15m. The shape of insulator arc discharge is multiple branch and the diameter ofinsulator arc discharge is decreased with the wind speed in10~15m.