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Surface Resistivity of Silicone Rubber Formulations Tested in Room Ambient Conditions: The case of silicone rubber formulations with and without filler materials
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Authors: Aviti Thadei & Dr. Alexander Kyaruzi
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U N I V E R S I T Y
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• The objective of this paper is to measure the surface resistivity of silicone rubber formulations used for manufacturing housings and sheds of composite polymeric insulators. The objective has two parts: (1) to manufacture the samples, and (2) to test the samples.
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• Test specimens were – Laboratory made samples, and – Industrially made samples.
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• With these formulations there was silicone rubber with and without filler materials
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• Testing conditions were room ambient temperature (22˚C - 25˚C) and humidity (32% – 40%).
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• The testing voltage was supplied by an Electrometer.
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• Resistivity values are shown in Fig 1.
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• S1 and S2 show differing values, although both are not stable.
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• S481 and S482 show differing but stable values.
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• SF1 and SF2 show similar values which are stable
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• PS shows stable values which are lower than those for SF1 and SF2
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Resistivity Results
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Fig.1: Silicone rubber samples surface resistivity variation with time for the first 50 minutes. The conditions of the test were room temperature, pressure and humidity i.e. temperature = 22 ˚C – 25 ˚C, humidity = 32%-40 %.
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Table 1: Average Surface Resistivity and Surface Resistance Values from Resistivity Measurements
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Material Sample
Name
Silicone rubber
S SF PS
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Surface Resistivity (Ω/square) 2 x 1017 4 x 1017 2 x 1017
Surface Resista nce (Ω) 4 x 1015 8 x 1015 4 x 1015
These values were obtained 5 minutes after starting energizing the samples
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U N I V E R S I T
• Differing values for samples S1, S2, S481 and S482 rubbers could be due to contact prblem.
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• Samples retained charges implying polarization by the DC voltage and higher relaxation times of the rubbers.
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U N I V E R S I T Y
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• If the dc energization was done for longer than 50 minutes the resistivity values continued to increase up to the point that the data obtained was not useful. • Fig. 1 shows that the empirical current that traverses the surface of the insulating materials does not decay exponentially but rather as an exponential power of the time as by equation I = Iot-n 10
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Future work
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• To fit the data obtained into the equation suggested by (Dakin, 2006). • To measure surface resistances of aged silicone rubber samples and compare with the values of new samples.
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