Verification of thermal rating calculations for high temperature low sag (HTLS) conductors

摘要

A measure for uprating the power transfer capability of an overhead line can be reconductoring. Therefore high temperature low sag conductors (HTLS) are taken into account as one technology beside others to solve the problem of bottlenecks in the grid. HTLS are capable of operating at temperatures in the range from 150°C to 210°C and enable an ampacity of ～150 to ～200 percent range of conventional conductors of the same diameter. To ensure a secure operation of the transmission line it is necessary to calculate the precise behavior of the conductor and to forecast the sag in every operating status. Cigre Technical Brochure 601 includes calculation methods to meet the demands for HTLS. The main aim of this paper is to verify the calculations by laboratory tests. For this purpose HTLS conductors of type ACCR and ACCC are investigated. Both conductor types are installed in the laboratory and the surface temperature as well as the core temperature is measured. Besides the tension and the current, the conductor can be subjected to specific ambient conditions, like simulated solar radiation, wind and ambient temperature. Calculations according to Cigre TB 601 and TB 207 are compared to measurements regarding the AC-resistance, the radial thermal conductivity, the surface temperature distribution and the influence of convective cooling on the surface temperature. The measurement results regarding the AC resistance indicate a linear dependence from the conductor temperature and fit to the calculations. For the radial thermal conductivity the TB 601 model assumes a temperature independent diameter, which is in contrast to the observed "bird caging" effect, which should result in a temperature dependent diameter of the conductor above the knee point. The measured and calculated surface temperatures are very close together up to about 100°C. With an increasing surface temperature the deviation of measurement and calculation increases for TB 601 and TB 207. Thereby TB 601 overestimates and TB 207 underestimates the measurement for ACCC and ACCR conductor. The effect of convective cooling seems to be underestimated in the calculation since the difference to the measured temperature slightly increases up to 17 K with an increasing wind speed up to 2.4 m/s.