Determination of Insulators Properties

Determination of Insulators Properties is related with their applications. The properties of the insulators namely, shrinkage, water absorption, porosity and bulk density were carried according to (ASTM, 1985a).

Insulators

Determination of Insulators Properties:
Linear Shrinkage:

The dimensional changes in length were taken and the results were used to determine the linear shrinkage after firing at 12000C. The linear shrinkage was determined using equations (1) to (3) below. (Norton, 1980; ASTM, 1985a; Clay Shrinkage Testing, 2010)

Water Absorption:
The boiling method was used for this test at 1000C for 2 hours. The test pieces were subjected to a two-hour boiling followed by an additional four-hour water soaking. Water absorption was calculated as a function of the specimen’s weight difference prior to and after water submersion. The water absorption was computed using equation (4). (Norton, 1980; ASTM, 1985a; Water Absorption, 2010)

Porosity:
The boiling method was used for this test at 1000C for 2 hours. The test pieces were subjected to a two-hour boiling followed by an additional four-hour water soaking and then weighed Ws. The soaked piece was then suspended from the beam of a balance in a vessel of water so arranged that the test piece under consideration was completely immersed in the water without touching the side of the vessel. The suspended specimen in water weighed as Wsp. Porosity was then calculated as a function of the specimen’s weight difference between soaked weight and dry weight to specimen’s weight difference between soaked weight and suspended immersed weight. The results were obtained by equation (5). (Norton, 1980; ASTM, 1985a; Calculate Apparent Porosity, 2010)

Bulk Density:
Bulk density was calculated using a direct volume measurement method. This method exploits the relative density of a substance multiplied by the density of water to obtain the required bulk density. Equation (6) was used to obtain the bulk density in g/cm3

Failing Load:
The strength of the porcelain insulators was investigated by determining their failing load according to (ASTM, 1985b). A Universal tensile testing machine was used to carry out the failing load of the samples. The insulators were coupled on the tensile machine and allowed to be loaded up to 20 kN until failure was experienced. The force at which the materials failed were recorded as presented in Table 3.
Physical Properties of Porcelain Insulators

Insulation Resistance:
Digital High Voltage Insulation Tester (Model TIN6N) was used to test the insulation resistance of each sample after firing at 1,200 0C. A gas-operated kiln was used to fire the materials with analog pyrometer to measure the temperature schedule with respect to time in hours. The insulators were fired for 8 hours as indicated in Figure 1. Different voltages were then injected into the samples to determine the breakdown voltage for each sample. The positive and negative terminals of the instrument were clipped at either end of the insulators and different voltages were injected by pressing the desire voltage button per time until the monitoring screen shows discontinuity sign which indicated the breakdown voltage.


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