317 / 2018-09-26 00:19:35

Industrial Pollution Impact on Outdoor High Voltage Insulator Performance

Acid rain,,partial discharge,insulator,Pollution

Loss of electrical power supply is an undesirable event as it causes huge cost and inconveniences to both suppliers and consumers. A power outage of a huge scale may originate from a fault in a piece of equipment in the generation/ transmission / distribution system (such as an insulator); spreading across the entire system. The insulator is an integral component of power transmission/ distribution and pollution accumulation on an insulator could trigger a failure process, which could be easily avoided. In industrial areas, anthropogenic pollution effects on High Voltage (HV) insulators resulting from acid precipitation (rainfall, snow and fog) deposition on insulators have been known to cause partial discharge (PD) activities and insulator flashover. Thus, an in-depth knowledge of the mechanisms of insulator pollution in industrial regions and a study of processes leading to an insulator failure will aid in predictive maintenance procedures and help prevent undesired power outages. In this work, a string of glass cap-and-pin insulator exposed to acid rain contamination is simulated in a HV Laboratory. The experiment is carried out on a standard glass disc insulator located in an environment chamber. The chamber offers control of temperature, humidity, fog and rainfall, to achieve the desired weather conditions of a chosen geographical region. As sulphuric acid (H2SO4) is a major constituent of acid rain, H2SO4 of known concentration is used for insulator contamination. Pollution severity is modelled to represent various levels of pollution obtainable in industrial areas by varying the concentration of the acid, using secondary data obtained in the field. To achieve a uniform pollution and adhesion, H2SO4 is mixed with a known quantity of kaolin and the insulator string is dipped into the mixture, removed and allowed to dry in a fume hood. The dry insulator string is set up in the environment chamber and cold fog applied to it. Voltage is supplied by a 10kVA, 100kV transformer which is controlled using a HV module to achieve desired voltage levels. A combination of High Frequency Current Transformer (HFCT) and radio frequency (RF) antenna is used for PD detection. A digital storage oscilloscope is used to acquire measured signal and measurement data is exported and analysed using a third party software in a computer. Two cases were considered in the experiment. For the first case, the voltage is kept constant while fog is gradually introduced to the polluted insulator, while for the second case; the pre-contaminated insulator is first wetted with fog, before being subjected to a slowly rising high voltage. For both cases, partial discharge activities were observed for as low as 5% concentration of the acid and flashover was observed at higher concentrations and voltages. When the polluted insulator was subjected to long periods of simulated rain, its performance improved under similar conditions. This can be explained as natural cleansing due to rainfall and plays a major role in the pollution mechanism and flashover process of exposed insulators. Results from this work are expected to be applied in asset management of HV equipment in heavy industrial areas, in preventive and predictive maintenance activities.