Thermal Rating Calculation Of The Grid-connected Line Of The Wind Farm In Zaozhuang Region Considering Thermal Aging Process Of Overhead Conductors

At present,the rapid increase of wind power installation capacity aggravates the power flow of the grid-connected lines of wind farms.Under this condition,the conservative nature of the traditional static thermal rating（STR）became one of the important factors that restricts the wind power integration.To this issue,speeding up the construction of power grids is an effective way to alleviate the lack of power transfer capacity,but the power grid construction is land source-occupying,and time-consuming,besides,wind power has the nature of strong volatility and low power generation efficiency（the number of the annual utilization hour of wind power is only about 2000）.Therefore,the blind expansion of the power grid will incur the low efficiency of the grid-connected lines of wind farms and affect the economic benefits of power grid construction.Under this circumstance,fully exploiting the current-carrying potential of existing grid-connected lines to accommodate wind power is undoubtedly the preferred way to alleviate the contradiction between the rapidly growing demand for wind power consumption and the relatively slow power grid construction.The essence of the current-carrying capability of the transmission component lies in the thermal limit of the conductor,which is determined by the conductor thermal aging limit.For example,the maximum allowable operating temperature of the ACSR conductor is set to 70℃ in China（large spans can be set to 80℃）because there is almost no thermal aging loss（conductor tensile strength）after the conductors are continuously operated at 70℃ for 2000 hours.However,for the grid-connected overhead lines of wind farms,the current and meteorological environment of the lines are volatile,which also brings about the volatility of conductor temperature.Under this circumstance,the maximum allowable operating temperature cannot reflect the realistic current-carrying capability of the grid-connected lines.According to the wind power construction plan in Zaozhuang region,some wind farms will face the limitation of the current-carrying capability of the grid-connected lines.This dissertation takes the grid-connected line of a wind farm in Zaozhuang as the research object,grasps the thermal limitation nature of its current-carrying capacity,and proposes The current-carrying capacity calculation method under the constraints of thermal aging of the conductor makes the calculation result of the current-carrying capacity more in line with its actual current-carrying capacity.The specific work includes:（1）The relationship between the operating temperature of the overhead conductor and the life and sag is studied and the mathematical model（2）The generation method of wind power output power and meteorological environment time series around the wire used to simulate the thermal aging process during the service life of the wire is studied;（3）The goal is to minimize the sum of wind abandonment loss and tower height The allowable cumulative tensile strength loss rate during the expected service life of the transmission line and the safety net distance between the conductors and the ground are constraints.An optimal decision-making model for the thermal setting of the transmission line is constructed and a heuristic solution method is proposed.The current-carrying capacity calculation method proposed in the dissertation does not need to set the maximum allowable operating temperature of the conductor.It can reasonably increase the thermal rating of the overhead line for the grid-connected lines of wind farms on the basis of directly considering the service life and sag limits of the overhead line,which can overcome the conservativeness of the temperature setting and can effectively improve the utilization efficiency of the grid-connected lines of wind farms,thus enhancing the wind power accommodation ability of the power system.In this paper,the simulations on a grid-connected line of a wind farm in Zaozhuang region are carried out to verify the validity of the current carrying capacity calculation method proposed in the paper.