Special contaminant such as organic matter needs to be considered in pollution flashover prediction and leakage current research.This paper analyzes the material properties of glucose,and studies the discharge characteristics of glucose contaminant external insulation under different humidities.This paper has studied the influence of glucose contaminant on insulator leakage current,and has analyzed leakage current amplitude,fundamental current amplitude,3rd harmonic current amplitude and phase.Test results show that insulator leakage current is affected by adding glucose into contaminant,and extent depends on atmospheric humidity and the amount of glucose contaminant.As the amount of glucose is above 0.1 mg/cm2,the leakage current amplitude of glucose sample is much larger than that of normal sample at the humidity of 60％.Glucose has good hydroscopicity.If glucose is added into contaminant,pollution layer will absorb more water;leakage current will increase and discharge will happen.

Wet contaminant is an important precondition for pollution insulation discharge.Wet process is affected by the atmospheric environment and the hygroscopicity together.We analyzed the moisture absorption of soluble and non-soluble substances,and chosed aluminium phosphate as a strong hygroscopicity material.The discharge test of pollution insulation was performed in constant humidity condition.Some leakage current characteristics were investigated to analyze the influences of non-soluble substance hygroscopicity,such as current waveform,fundamental current amplitude,3rd harmonic current amplitude,and phase.Test results show that insulator leakage current is affected by insoluble substance hygroscopicity,and the influential extent depends on atmospheric humidity and the mount of strong hygroscopicity material.As the amount of aluminium phosphate exceeds 20％,the leakage current amplitude of aluminium phosphate is much larger than that of normal sample at the relative humidity of 70％.The phase between fundamental current and voltage is sensitive to the hygroscopicity of pollution layer.Hygroscopicity is the natural quality of pollution layer,which cannot be covered in the investigation of atmospheric humidity and pollution severity.

500 k V港城变电站在较低湿度下,其外绝缘发生大面积放电现象。为此采用化学分析与电气测试的方法,对该现象进行研究。化学模拟计算表明,磷酸铝的多孔结构增大了其比表面积,可吸附更多的水分子;同时结构中的桥位氧原子与四配位铝原子都可以与水分子形成化学键,增强了磷酸铝的吸湿性。人工污秽试验表明:非饱和湿度下,磷酸铝污秽绝缘子起始放电电压远低于常规污秽;相对湿度70%、盐密0.20 mg/cm2时,常规污秽绝缘子起始放电电压为17.5 k V,灰分中磷酸铝质量分数为20%的污秽绝缘子起始放电电压降至10.0 k V。研究结果表明,磷酸铝污秽具备的强吸湿性,是港城站外绝缘在较低湿度下放电的主要原因。污秽物吸湿性会影响低湿度下外绝缘放电特性,强吸湿性污秽将降低外绝缘放电所需的湿度要求。

Contaminant composition affects the discharge characteristics of external insulation. This paper studies the intense discharge phenomenon at low relative humidity (77%) in an AC 500 kV substation in Southern China. Due to farming and the soil feature in the sugar cane field around the substation, aluminum phosphate is formed in the soil, and accumulates on the external insulation surface owing to blowing dust. The porous structure and four-coordinated aluminum atom lead to strong moisture absorption capacity of aluminum phosphate. Then electrical performances of aluminum phosphate as a contaminant on insulation surface were investigated by means of discharge test in a constant humidity chamber. The experimental results show that, compared to conventional contaminant, aluminum phosphate contamination insulator has lower discharge inception voltage and stronger discharge intensity when relative humidity is above 70% and the aluminum phosphate content exceeds 20% in the non-soluble deposit. Aluminum phosphate is the main cause for the discharge phenomenon in the substation under study. It needs to be considered for insulation design and maintenance in ferralsol areas where phosphate fertilizer is heavily used. The moisture absorption of contaminant merits special consideration for further research.

In recent years it is discovered that there are large amounts of organic in the contaminant on insulation surface. There are some special discharge phenomenon appeared in many place. Influence of organic on insulator discharge is very scarce. This paper studied a strong discharge activity under low humidity which was caused by the glucose contained in contaminant. The influence of glucose on insulator under low humidity is studied by chemical analysis, simulation tests, flashover tests and chemical calculations. The results show that because of the strong moisture absorption of glucose, the leakage current of polluted insulator with glucose is much larger than the conventional polluted insulator, as the content of glucose exceeds 0.10mg/cm2. The thermal effect of leakage current makes the surface potential distribution of glucose polluted insulator more uniform, and reduces the initial discharge voltage of the polluted insulator. At the same time glucose possess a active chemical property, the bonds of glucose could be broken to generate free radicals with electric charge in the strong electric field or discharge. It enhances the electron transfer rate, and strengthens the discharge intensity. Physical and chemical properties of glucose cause the special discharge phenomenon.