A Ccr A Conf 2008

U N I V E R S I T Y

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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U N I V E R S I T

• 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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U N I V E R S I T

• 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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U N I V E R

• 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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U N I V E R S I

• 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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U N I V

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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