Research On Ice-melting Technology Of Overhead Lines With Alternative Current

Line-icing is a serious threat to power system. Thermal ice-melting technology, which uses Joule heat generated by the current flowing through the lines to melt ice, is the most direct, effective and reliable de-icing technology now to solve overhead lines icing problem. However, there are still some defects such as too large reactive power consumption for alternative current (AC) ice-melting and too expensive investment for direct current (DC) ice-melting due to additional devices of DC power. As the construction of Ultra-high voltage (UHV) power grid and the emergence of more and more power lines with larger cross-section, it is essential to develop more practical icing-melting method.Differing from the existing thermal ice-melting technology for overhead lines, a new AC ice-melting method with a heater, bifilarly wound by insulated cooper wires and set along the axis of overhead lines, is proposed. There are two benefits for the bifilar heater, one is non-inductive and almost equivalent to a pure resistance; the other carries AC current to melt ice and DC power is not necessary so that cost can be greatly saved.In order to improve the heat transfer efficiency of ice-melting lines, the gap among wires of overhead line is filled by mixture of epoxy resin and Aluminum Nitride (AlN), a kind of semi-conductor powder with high thermal conductivity. Based on the principles of heat transfer, this paper performs an analysis on inner temperature field of ice-melting lines with thermal field and thermal circuit methods, respectively. After preparing some specimen, the temperature-rise experiment is also carried out. Experimental results and theoretical analyses have manifested that mixture of AlN and epoxy resin filled in lines not only enhances the thermal conductivity but also increases the heat transfer area, which obviously improves the heat transfer efficiency of lines, the temperature difference between inner and outer layers of power lines is greatly decreased, that is, the maximum temperature rise in inner of lines is effectively reduced.According to the proposed method, the ice-melting experiment is implemented, the experimental results verify the feasibility of the ice-melting method. Effects of adding AlN mixture on ice-melting efficiency are studied from the perspective of power and temperature. When the ice-melting current is fixed with constant power, the result indicates that adding AlN mixture has slight impact on ice-melting efficiency, but the inner temperature rise significantly decreases and the range of ice-melting current permit to increases further. Consequently, adding AlN mixture obviously shortens ice-melting time and improves ice-melting efficiency with the circumstance of the same dynamically stable inner temperature rise due to the increase of current-carrying capacity.