【作者】 王大兴；

【导师】 蒋兴良；

【作者基本信息】 重庆大学 ， 电气工程， 2010， 硕士

【摘要】 输电线路是电能传输的重要设备,线路覆冰给电力系统的安全稳定运行造成严重威胁。到目前为止,国内外还没有一种理想的针对输电线路的除冰防冰方法,相对而言采用短路融冰方法具有融冰速度快、融冰效果好等优点,是防止电网发生冰灾的可行方法之一。在融冰过程要求输电线路温度高于临界融冰温度,又不超过线路的允许温度范围,是目前没有很好解决的技术难题。因此展开对融冰过程中导线表面温度特性的研究,能保证输电线路有效融冰且确保融冰过程中不损伤导线,是合理设计电流融冰装置、因地制宜实施融冰方法的技术基础,为电网快速有效除冰提供必要的保证。本文依托国家重点基础研究发展计划项目(973项目:2009CB724501)和“十一五”国家科技支撑计划重大项目(2006BAA02A19),以我国输电线路所采用的两种典型导线为例,在大型多功能人工气候室中模拟输电线路自然覆冰进行短路电流融冰试验,利用电流发生器、桥式整流器和高精度实时温度监测系统,对交直流短路融冰过程中导线表面温度特性进行试验研究。论文分析了短路融冰的临界条件,建立了临界电流融冰的数学物理模型,研究各种因素对临界融冰电流的影响规律,并提出了临界融冰电流的计算公式。结合短路电流融冰的热平衡过程,建立电流融冰的数学物理模型,利用控制体积法对融冰过程中导线表面温度分布进行数值计算,分析了各种因素(空气间隙、风速、环境温度、覆冰均匀程度等)对导线表面温度分布的影响规律。并对融冰过程导线最高温度特性及其影响因素进行分析。研究表明:在临界融冰状态导线表面的温度始终保持0℃,若要进行短路电流融冰,融冰电流必须要大于临界融冰电流。临界融冰电流随着风速的增大而增大、随环境温度的降低而增大,而与冰层厚度的大小关系不明显。临界融冰电流的计算结果与试验结果基本一致,其相对误差为1%~9%。融冰开始后,随着空气间隙的产生,导线表面温度分布不均匀。导线上表面温度始终为冰层融化的温度,导线下表面温度随着空气间隙的增加而增大,当冰层从导线上脱落的时刻导线温度达到最高。在融冰过程中,冰层的内表面始终为冰水混合物,其温度为0℃。通过本文建立的椭圆形短路电流融冰模型,分析了空气间隙是影响导线温度分布的主要因素;风速和环境温度的变化仅影响冰层的融化速度,对导线表面温度分布没有影响,只是通过影响空气间隙变化快慢间接地影响导线表面温度的温升速度;同时导线覆冰的均匀程度对导线表面温度分布也有一定的影响。经数值计算得到的温度特性曲线与试验数据对比其结果基本吻合。通过分析,导线表面温度只取决于融冰电流和空气间隙而与外界条件无关。结合传热学理论,提出了计及融冰电流和冰层厚度影响的导线表面最高温度的计算公式,并可采用本文提出的方法计算最大允许融冰电流。更多还原

【Abstract】 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.更多还原