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 a particular application.
Dielectric properties that are considered while 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 a measurement of direct current flow into the insulator when subjected to electrification up to one minute. It value varies from 109 to 1020 ohm-cm at ambient conditions.
Dielectric Polarisation: This is the displacement occurs in the material of it dipoles when an electric field is supplied to a dielectric material. Due to the non-flow of charge in the dielectric material its interior section has non-equipotential which make a charge to be absorbed by the formula,
Dielectric absorbed charge = capacitance of dielectric material X voltage applied to its surface.
Dielectric constant: This is the property that describes the capacity of the material to store charge in the presences of the electric field. It is expressed as the electrical capacities ratio of the condenser with material and without material filled with vacuum. The 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 an electric potential. The factors affecting dielectric strength are,
- The thickness of material,
- Time of application of electric current,
- Frequency of applied electric field,
- Humidity and
If these factors are increased correspondingly dielectric strength decreases.
Dielectric loses: It is the loss of electrical energy through the leak in insulating material. Electric insulator components should not absorb electrical energy. Even after removing an electric field from them, its capacitor charge should be recovered without loss. The loose 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. Power factor determines the power loss from the insulator.
Temperature and Heat resistance: Due to long operation insulators gets heat up. They should be able to resist the heat evolved and maintain other properties with alteration.
Mechanical strength: The compressive strength and tensile strength of an insulator depending on the porosity of the material. This factor is taken care during manufacturing. Specification of each insulator is standardized in making process.
Thermal ageing: Due to prolonged exposure to heat. The effect of temperature changes its mechanical properties due to change in its structure. Based on the material it is formed the compounds may react with water present in the air as moisture. Also with the oxygen present surrounding it.