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R.N.G.P.I.T, Bardoli �Electrical Engineering Department

Subject: EMMI

Prepared By:

Dr. Shaikh Mohammed Suhel

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Prepared By:

Name: Dr. Shaikh Mohammed Suhel

(Assistant Professor RNGPIT, Surat)

Former Assistant Professor in SCET, SNPIT&RC, VIT
Qualification: PhD (Power- Electronics & Drives, NIT, Surat), M.Tech (Industrial Electronics, NIT-Surat), Gate, B.E. (Electrical Engineering., VNSGU-Surat).
Experience: 13 Years.

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CH: Electrical Engineering Materials

This Lecture contain
Dielectric Materials & It’s Application, Dielectric losses, solid dielectric

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Relative Permittivity or Dielectric Constant:

>Dielectric characteristics are determined by dielectric constant, ε_r

>It is defined as the ratio between the permittivity of the medium ε and the permittivity of free space ε_o.

> ε_ris dimension less quantity and varies widely from material to material. Its value for vacuum is 1, and for all other dielectric it is always greater than 1.

>Permittivity of a medium indicates the polarizable nature of a material.

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Dielectric Losses or Loss tangent:

>loss of energy that goes into heating a dielectric material in a varying electric field.

>It can be understand by taking the case of charging and discharging of a capacitor, if V is the potential, then amount of energy stored in the form of electrostatic potential energy in the dielectrics.

>during discharging the same energy should be released but it is an observation only a part of it is released while rest is disappeared as a heat.

The amount of energy dissipated in the form of heat is known as dielectric loss.

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Dielectric Losses or Loss tangent:

>Let the plate of capacitor is placed in an electric field ,due to field dipoles orient in a particular direction and opposes by internal friction. The opposition by dipoles is equivalent to resistance of capacitor.

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Types of Dielectric Materials:

>Dielectric materials can be solid, liquid or gaseous.

>Solid dielectric are most commonly used in electrical equipment as these are very good insulator.

>Example: Porcelain, glass, plastic, rubber cotton, wood and mica.

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Types of Dielectric Materials:

>Liquid Dielectric materials are basically three different types: (1)mineral insulating oils

(2) Synthetic insulating oils.

(3)Miscellaneous insulating oils.

>The function of insulating liquids is to provide electrical insulation and to dissipate heat (cooling agent).

>Example: Transformer oil, cable oil, capacitor oil, vegetable oil, vaseline, silicon liquids, Sovol, and Sovtol.

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Types of Dielectric Materials:

>Gaseous Dielectric materials are used both as insulator and as cooling agents

>Example: Air, hydrogen, nitrogen, helium, sulphur-dioxide, propane, methane, sulphurhexafluoride.

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Solid Dielectric Materials:

>Mica: Mica is an inorganic mineral material, made of the silicate of aluminum with silicates of soda, potash and magnesia. It is crystalline in nature and can be divided into very thin flat sheets.

It is rigid, tough and strong. It has high dielectric strength and low dielectric losses. It is not affected by moisture.

Application:

Electric Irons, hot plates and toasters.

Insulation in armature and field coils, high frequency application.

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Solid Dielectric Materials:

>Glass: Glass is an inorganic material made by the fusion of different oxides like SiO₂,ZnO and MgO.

Glass is brittle and hard. It has good mechanical strength and has low dielectric loss. It is insoluble in water and is highly chemical resistant to most corrosive agent.