Qifa Wan

AC Conductors' Corona-Loss Calculation and Analysis in Corona Cage

Corona loss generated from conductors is one of the important design factors of extremely high-voltage ultra-high voltage (EHV/UHV) ac transmission lines. The charge simulation method was adopted to calculate conductor corona loss in the corona cage. Every corona cage wall is equivalent to the ground plane and, therefore, the calculation model is more complicated than the power-line model above the ground surface. Two corona cages-UHV corona cage and small corona cage-were adopted in the tests. The cages are both square sections. Single conductors and bundle conductors were tested in the corona cages to verify the corona cage calculation model. And the same type of conductor was tested in the small corona cage and in the UHV corona cage to check the measuring system and the simulation program of corona loss further. Since the artificial rain rates were from 12 to 20 mm/h, corona losses were measured and calculated. The results indicate that the fundamental frequency component is the most main component of corona loss. The corona cage corona-loss calculation model is appropriate. And for single conductor LGJ-500/35 and bundle conductors, 8 LGJ-500/35, under heavy rain conditions, with the rain rate being from 12 to 20 mm/h, the roughness coefficient range is from 0.4 to 0.5 approximately.

500-kV EHV Bundle Conductors' Corona Onset Voltage Calculation and Analysis in Corona Cage at Different Altitudes

In order to research an altitudes effect on corona onset voltage of bundle conductors in a corona cage, a calculation model was established, and corresponding test proceeded. The charge simulation method was adopted to calculate space electric-ήeld strength. According to self-sustained discharge criterion in a severe nonuniform electric ήeld, and variation of altitude, the corona onset voltage calculation model of bundle conductors in a corona cage was established. The corona onset voltages of bundle conductors, which were used in the 500-kV extremely high voltage transmission line, were tested at different altitude locations, as Wuhan 19 m, Xining 2261 m, Golmud 2829 m, and Nachitai 3800 m. Corona onset voltages of 4 × LGJ - 0400/5 and 4 × LGJ - 300/25 were obtained. The corona onset voltage curves at different altitude, bundle spacing, and bundle numbers were obtained. The analysis shows that the model can be used to provide accurate values of corona onset voltage for bundled stranded conductors in the corona cage at various altitudes. With bundle spacing from 350 to 500 mm, the corona onset voltage decreases as bundle spacing increases, and the onset voltage increases as the bundle number increases. As altitude increases every 1000 m, the corona onset voltage of bundle conductors decreases by about 8.5%.

UHV AC corona loss measurement and analysis under rain

Transmission line corona loss research is one of the critical technologies of 1000kV UHV transmission and transformation engineering. Transmission line corona loss relates with many factors of climate, and rainfall rate effects corona loss distinctly very much. By means of UHV AC single circuit test line corona loss monitoring and UHV corona cage conductor corona loss measurement, this paper researched the effect of rainfall rates to UHV AC single circuit transmission lines corona loss. This paper applied corona loss monitoring system to monitor corona loss of UHV single circuit test line, and obtained corona loss monitoring data in light rain, moderate rain, and heavy rain conditions. Analyze corona loss test results. Corona loss value in light rain, moderate rain, and heavy rain conditions are obtained. The results show that, rain has an obvious influence on corona loss of the line, at the beginning of raining, corona loss increases quickly, after rain, corona loss decreases with drying of the conductor. Decay time is related with surface field strength, wind speed, air humidity, temperature and other factors. When rainfall rate is low, corona loss increases fast with the increase of the rainfall rate. With the increase of the rainfall rate, corona loss grows slowly. When rainfall rate increases to some level, corona loss stop growing.