Abstract
Currently there are no international standards for evaluating the tracking and erosion resistance of DC polymeric insulation under contaminated conditions. Researchers often modify the existing AC inclined plane test standards such as the IEC-60587 to accommodate DC voltage conditions but this has been reported to give various inconsistences. This paper presents comprehensive experimental results on inclined plane tests of silicone rubber (SiR) insulation at 3.5 and 4.5 kV AC and positive DC using intravenous (IV) system as the pollutant supply. The leakage currents (LC) were recorded throughout the entire tests. In addition, various physiochemical tests namely, Fourier Transform Infrared analysis, thermo-gravimetric analysis, scanning electron microscopy and energy dispersive spectroscopy were performed on the aged and unaged samples. Results show that DC LC is bigger (about three times) than that under AC for the same equivalent voltages. Furthermore, DC LC variations are less random and the average magnitudes increase with duration of voltage application compared with AC. The physiochemical analyses show that 3.5 kVrms AC and 3.5 kV DC aged samples have comparable chemical characteristics albeit with electrode corrosion elements detected on the DC aged samples. Under 4.5 kV DC the degradation becomes significantly more severe and unrepeatable. It is therefore concluded that at 0.3 ml/min, pollutant flow rate, 3.5 kV positive DC and 3.5 kVrms AC are comparable as test voltages for inclined plane accelerated ageing of SiR insulation.
Highlights
Among other possible outcomes in the evolutionary development of electrical insulation technology as reviewed by Li et al [1], silicon rubber composites (SiR) are a popular contemporary option
The measured leakage currents (LC), and material characterisation results of silicone rubber (SiR) test specimen aged at 3.5 kVrms and 3.5 kV DC at 0.3 ml/min pollutant flow rate are comparatively analysed and discussed
The percentage of non-arcing state was calculated to be 48% for the DC condition and 69% for the AC samples. This is in agreement with the observed physical damage where the AC samples which arced for 31% of the test duration showed less damage compared with the DC samples which arced for 52% of the total exposure time
Summary
Among other possible outcomes in the evolutionary development of electrical insulation technology as reviewed by Li et al [1], silicon rubber composites (SiR) are a popular contemporary option This insulation technology has been in existence for at least 50 years and mainly in outdoor high-voltage applications. For AC applications, the IEC-60587 [3] standard on inclined plane tests is a well-established technique to evaluate the tracking and erosion resistance of outdoor polymeric insulation. The modifications in the test procedures include use of the equivalent root mean square (RMS) voltage and increasing the creepage distance and/or varying the pollutant flow rates These adaptations are done to try and account for and normalise the differences in insulation degradation dynamics under AC and DC electric stress. The intention of this work is to experimentally compare and contrast AC and DC inclined plane tests on SiR insulation seeking to confirm and/or add more insights into this knowledge domain
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