特高压气体绝缘输电线路壳体出厂试验气密性检测方法研究

Research on Air Tightness Detection Method for Enclosure Routine Test of UHV Gas-insulated Transmission Line

正在建设的淮南-南京-上海1 000 kV交流特高压输变电工程长江大跨越的跨江输电采用了气体绝缘输电线路(gas-insulated transmission line, GIL),其GIL单个单元最大长度为18 m,外径达到900 mm,因此与一般的气体绝缘封闭开关设备(GIS)相比,GIL相对具有更大的发生内部绝缘气体泄漏的可能性。为了保证GIL运行时的绝缘强度并防止外界环境对于GIL内部的影响,以往要求小于等于0.5%/年的泄漏率已经不能满足,本工程将该要求提高到小于等于0.01%/年。文中的目的是研究在型式试验和出厂试验的气密性检测中可行的方法,并通过试验确定对提高出厂试验的效率极为关键的充氦保压时间这一参数。试验中分析了两种常见的气密性检测方法,提出为满足本工程要求应该使用真空箱氦检漏的气密性检测方案,然后利用标准漏率的漏孔和18 m GIL试品工件试验研究和论证了特高压长距离GIL壳体气密性检测中的充氦保压时间。试验结果表明真空箱氦检漏法足以满足本工程要求的GIL单元的气密性检测精度和效率,试验得到的充氦保压时间也为将真空箱氦检漏法推广用于特高压GIL的气密性出厂试验提供了依据。

Gas-insulated Transmission Line(GIL) is very suitable for the power transmission across the Changjiang River in Huainan-Nanjing-Shanghai 1000 kV UHV project because of its high reliability and long endurance.Because the size of GIL unit in this project are 18 m in length and 900 mm in diameter,the probability of leakage is higher than GIS whose leakage rate is≤0.5% per year in standard,and the leakage rate is prescribed as≤0.01%per year in this project in order to enhance the dielectric strength and to avoid the external influence.The object of this paper is to obtain an air tightness method that is useful in type test and routine test,and to determine the duration in keeping Helium pressure for leakage detection that is important for accuracy and efficiency in routine test.In the test,two common methods of air tightness detection are analyzed,and the air tightness detection scheme of helium leak detection of vacuum box is proposed to meet the requirements of the project.In addition,the duration in keeping Helium pressure for leakage detection of GIL is studied with standard leakage unit and 18 m GIL unit,respectively.The experimental results indicate that Helium leakage detection method is enough for leakage detection with the required accuracy and efficiency.Moreover,the duration in keeping Helium pressure is useful for employing Helium leakage detection in the routine test of UHV GIL.