Insulators or insulating materials are the chemical products used for blocking the flow of heat or electricity. Insulators are made depending on the requirement of the mechanical, chemical and thermal properties it should possess for particular application. Dielectric properties are considered will selecting an insulator.
Resistivity – Electrical conductivity: As per the term insulation it should have a property of resisting the flow of electric current. This is measurement of direct current flow into the insulator when subjected to electrification up to one minute. It value vary around 109 to 1020 ohm-cm at ambient conditions.
Dielectric Polarisation: This is the displacement occurs in the material of it dipoles when electric field is supplied to a dielectric material. Due to the non flow of charge in the dielectric material it interior section have non-equipotential which make a charge to be absorbed by the formula,
Dielectric absorbed charge = capacitance of dielectric material X voltage applied around it surface.
Dielectric constant: This is a property describes the capacity of the material to store charge in the presences of electric field. It is expressed as the electrical capacities ratio of the condenser with material and without material filled with vacuum. Dielectric constant value will be less for insulating material but for storage of electric energy this value should be high.
Dielectric strength: It is the ability of the insulator to withstand the puncture and rupture caused by electric potential. The factors affecting dielectric strength are, thickness of material, time of application of electric current, frequency of applied electric field, humidity and temperature if these factors are increased correspondingly dielectric strength decreases.
Dielectric loses: it is the loss of electrical energy through the leak in insulating material, these components should not absorb electrical energy and after removing electric field from them it capacitor charge should be recovered without loss. The lose angle should be zero and phase angle of 90oC.
Power factor: It is the sine function of loss angle and cosine function of phase angle. Its value nearly meets dissipation factor. It determines the power loss from insulator.
Temperature and Heat resistance: Due to long operation insulators are heat up and so they should be able to resist to the heat evolved and maintain other properties with alteration.
Mechanical strength: The compressive strength and tensile strength of an insulator depend on the porosity of the material and this is take care during manufacturing and specification are standardised in make process.
Thermal ageing: Due to prolong exposure to heat the effect of temperature the change it mechanical properties due to change in it structure of material formed, the compound may react with water present in the air as moisture and to the oxygen present surrounding to it.