- Dielectric or Dielectric Materials:
- are those substances same as insulators but will allow the flow of electron through them when subjected to an external electric field as they can be polarized. It also can be defined as the ability to store charge (energy) by mean of polarization such in a capacitor. Also, they are having high dielectric constant (Relative permittivity = εr).
- Examples: A common example of a dielectric is the electrically insulating material between the metallic plates of a capacitor, (such as mica, laminated paper). Other examples: air, ceramic etc.
- Application of Dielectric Materials
- A major application for inorganic materials is in high and medium voltage substation equipments and overhead lines as insulators or as bushings on high voltage transformers and switchgears.
- Plastic films have been used as films in a variety of applications such as the insulation between foils in capacitors and slot insulation in rotating electrical machines.
- Common use for flexible insulating sleevs is the protection of cables and components from the deleterious effects of mechanical and thermal damage, and may find application in electrical machines, transformers, domestic and heating appliances, light fittings, cable connections (joints and terminations) and switchgears.
- Resins and varnishes are used by in the impregnation and coating of electrical equipment (dry type transformers, as an example) in order to improve its resistance to working conditions, to enhance its electrical characteristics and to increase its working life.
- Elastomers and thermoplastics are commonly used in the insulation of power, control and communications cables.
- Nowadays the principal uses of liquid dielectrics, mainly hydrocarbon mineral oils, are as an insulation and cooling medium for transformers, earth reactors and shunt reactors, capacitors and rheostats.
- The important properties of dielectric liquids are therefore electric strength, viscosity, chemical stability and flashpoint.
- Two gases already in common use for insulation are nitrogen and sulphur hexafluoride (SF6). Nitrogen is used as an insulating medium in some sealed transformers and Gas Insulated Lines (GIL), while SF6 is used in in high and medium voltage switchgears and circuit breakers, because of its insulating properties and its arc-extinguishing capabilities, and also in Gas Insulated Transformers (GIT) as an insulation and cooling medium.
- However, due environmental conditions, in medium voltage installations (circuit breakers, contactors and capacitors) vacuum has nowadays a preferential use.
- You may also read: Corona Effect in Transmission Lines & Power System
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