Research On Temperature Characteristic Of Conductor And Its Influencing Factors During Ice-melting

Transmission lines are important power transmission equipments, transmission line icing poses a serious threat to the security and stability of power system. So far, it has not yet an ideal de-icing method for transmission line at home and abroad. In contrast, ice-melting method using short-circuit have short time and good effect of ice-melting and so on, is one of the methods for preventing the occurrence of ice damage. In the process of ice-melting, only if the temperature of conductor will be higher than the critical temperature and be not more than line allowed temperature range, ice layer melts. The method is not well resolved technical problems. Therefore, research on temperature characteristics of conductor in the process of ice-melting ensure effective ice-melting and not to damage the wire in ice-melting process, and provide the necessary guarantees for safe operation of the power grid.Supported by The National Basic Research Program of China (973 Program: 2009CB724501) and Key Project of the National Eleventh-Five Year Research Program of China(2006BAA02A19), this paper uses two kinds of transmission line conductors for the test product, and systematically investigates temperature characteristic of conductor and its influencing factors during ice-melting based on high-current generator and bridge rectifier and high-precision real-time temperature monitoring system by analoging transmission line icing and ice-melting using short-circuit in the artificial climate chamber.This paper established mathematical and physical model of the critical current of ice-melting, the influencing rule of a variety of factors on the critical current and ice surface temperature were also analyzed. In addition, the method to calculate the critical current and ice surface temperature was put forward. Combined with the thermal ice-melting with short-circuit current balance of during ice-melting, mathematical and physical model of ice melting was established, and control volume method was used for calculating temperature distribution of the surface of conductors. The various factors (air gap, wind velocity, environmental temperature and so on) were analyzed on temperature distribution of the wire surface. And the maximum conductor temperature characteristics and influencing factors were analyzed.Studies have shown that in the critical state of ice-melting surface temperature of conductor has been maintained at 0℃, current can only melt the ice when the current is greater than the critical current of ice-melting. Critical current of ice-melting increases along with the increase of wind speed and the decrease of temperature increase, while the size and thickness of ice is not obvious. Critical current of ice-melting calculations are basically consistent with the experimental results, the absolute value of error is between 1% and 9%.After the beginning of ice-melting, there is uneven distribution of surface temperature of conductor with the air gap formation. The upper surface temperature of wire is always melting temperature, the lower surface temperature increases with the increase of air gap. When the ice falls off the wire, the temperature reaches to the maximum value. In the process of ice-melting, the inner surface of ice layer is always the temperature of the ice water mixture and always is 0℃. In this paper, oval-shaped model through ice-melting is established, the impact of the air gap is considered as major factor in the distribution temperature of conductor, wind velocity and environmental temperature affect only the rate of ice-melting, and have no effect on surface temperature distribution of conductor. Only by influencing the speed of the air gap changes indirectly influence the rate of change in surface temperature leads. The uniformity of the ice also has certain influence on surface temperature distribution. Comparison of numerical results with the experimental data is basically consistent.The wire surface temperature depends only on the ice melting current and air gap theres with external conditions. A calculation formula for maximum temperature of conductor affected by the thickness of ice and ice-melting current is established according to the heat transfer theory, the method can calculate the maximum allowed ice-melting current.