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The Study on Leakage Current Characteristics and Electrical Properties of Uncoated Ceramic, RTV Silicon Rubber Coated Ceramic, and Semiconducting Glazed Outdoor Insulators

Insulator is one of the most important equipments in an electric power system. Failure of insulator may interrupt the electric energy delivery. The system reliability is greatly affected by the performance of the insulator. Therefore, ensuring the high performance of insulators has become indispensable. There are many methods to increase the performance of the outdoor insulator that are exposed to environmental conditions, such as temperature, humidity, and the presence of pollutants. Among the methods, applying room temperature vulcanized (RTV) silicone rubber coating and semiconducting glaze on the insulator surface are often used. This paper discusses the performance of uncoated ceramic insulator, RTV silicone rubber coated insulator, and semiconducting glazed insulator (SGI), as well as the comparison result among them. The performance is indicated by measuring leakage current (LC), surface temperature, and hydrophobicity. In addition, computer simulation on outdoor insulators using ATPDraw software is also conducted for LC waveform resulted by each type of insulator in order to study the electrical properties of each insulator. In the simulation, an outdoor insulator is represented by an electrical circuit model consisting of capacitors, nonlinear resistors, and number of arc models. AC voltage is applied to the model and the current is monitored. Hence, some key parameters of LC waveform are required to determine the similarity between measured LC waveform and simulated LC waveform, which are LC magnitude, Total Harmonic Distortion (THD), and dominant harmonic number. Experiment results showed that LC waveform and magnitude are strongly affected by the applied voltage, environmental condition, and the condition of the insulator surface itself. Specifically for SGI, LC waveforms are generally similar with the sinusoidal applied voltage. The LC waveforms are also symmetrical for positive and negative half cycles and no flashover was observed for applied voltage up to 40 kV. The hydrophobicity of insulator surface decreases after the experiments, with the pollutant presence and salt fog condition cause higher reduction compared to the clean samples and in clean fog environment. SGI has higher hydrophobicity compared to ceramic insulator. Field-aged RTV silicone rubber coated insulator shows higher hydrophobicity compared to field-aged uncoated ceramic insulator. At the end of the 6 year, the difference of contact angle between the two types of insulators can reach up to 50 – 60°. This proves that less pollutant is likely to stick on coated insulators for long time. The LC waveforms obtained from all experiments both in the laboratory or in the field have been successfully simulated through computer simulation. The simulation indicated that SGI is more capacitive than normal ceramic insulator and has lower values of piecewise resistance of the nonlinear resistance, resulting LC flow on the insulator surface also much higher. Despite the increased applied voltage, SGI shows very little discharge on its LC waveform, hence it has only 2 arc models, while at higher applied voltage, ceramic insulator has many discharges occur along the LC waveform, hence the arc models for this insulator can reach up to 9 arc models. Received: January 24, 2018. Accepted: June 23, 2018 DOI: 10.15676/ijeei.2018.10.2.9