Study On The Short-term Overload Capacity Of Overhead Lines Under A State Of Emergency

According to China Power Industry Standard DL755-2001 Guidelines for power system stability,the operation of 220 kV and above transmission lines should meet N-1 principle.Based on DL755-2001,the non-parallel operation schedule of 110 kV transmission-lines section is determined by long-term allowable current-carrying capacity,meanwhile the parallel operation schedule of 110 kV transmission-lines section is determined by N-1 principle.The N-1 operation modes include special strategies and emergency strategies.The control cross-section of transmission lines depend on the emergency operation current-carrying capacity,whose value determines the transmission capacity to a great extent.The transmission capacity under normal operation mode is restricted and wasteful without consideration of overload ability,as the current-carrying capacity under N-1 operation mode is determined by its long-term allowable value.Based on the operation status of Guangdong power grid,the short-time overload ability of overhead transmission line is proposed by this paper.The safety performance of transmission lines are assessed by analyzing the environmental meteorological condition,the temperature rise characteristic,sag characteristic,the permanent fault probability,the high-temperature performance of conductors and fittings.The feasibility of improving the operation temperature for transmission lines under emergency modes is assessed,and correspondingly the feasibility of short-time overload operation for transmission lines.The 30 minutes short-time operation schedules with 1.2 or 1.4 times long-term allowable current-carrying capacity are proposed and verified practically by this paper.The application conditions and control measures are proposed for the failures under short-time over-load operation of transmission lines at the same time.