Dielectric Material, Dielectric strength, Dielectric loss and loss angle

Friends,
In my previous post Insulating material and their properties We have discussed about various properties and need of insulating materials in electrical industries. In my current article I will discuss about the term Dielectric Materials.

What is a Dielectric Material

Dielectric material is typically an insulating material that is used in capacitors to store charge. As we know that in capacitor there are two separate plates that store opposite charges and that's how we store electrical energy in the form of charge in capacitors. Now the important thing is that if we fill the gap between these plates with an insulating material then the capacity of the capacitance to store charge increases. that's where dielectric play its role. So, Dielectric materials are the materials used to store electric charge in a capacitor. However there is nothing called ideal still there are some characteristics that an ideal dielectric material must have. These are :

• Zero Dielectric Loss Angle
• No dielectric loss
• Current leads voltage by an angle of 90 degrees

What is Dielectric Strength

The maximum potential gradient that an insulating material or dielectric can withstand without its mechanical breakdown is called its dielectric strength. The voltage corresponding to dielectric strength is called breakdown voltage and is expressed in kV/mm. This voltage disturbs the electric as well as mechanical properties of the material.

Factors on Which Dielectric strength depends

However their are a number of factors on which dielectric strength of a material depends, but some of the common factors are discussed below :

• Temperature:As we know that with the change of temperature the movement of electrons in a material changes and hence it affects the breakdown voltage of the material.
• Humidity:Water is no doubt a good conductor of electricity ( Not pure water although :( ). thus deposition of water on the surface of material creates some short circuit paths on material ultimately reducing its breakdown voltage.
• Frequency of Applied Voltage: Frequency has a direct relation with the breakdown voltage or dielectric strength. An increase in the frequency will result in increased dielectric strength.
• Thickness of Material: Thickness is very simple concept. In an electrical material if the thickness of material is increases its breakdown voltage is also increased.

What is Dielectric Loss And Loss Angle

When an insulating material is subjected to alternating voltage (a.c.), some of the electrical energy is absorbed by the insulating material and this energy is dissipated as heat. This amount of energy absorbed by the material is called Dielectric loss.
In case of a perfect Dielectric material current leads the voltage by 90 degrees but this is not the case with practically available dielectric materials.in practical case it is less than 90 degrees say it angle Ѳ. Now the difference 90-Ѳ is called loss angle and is very important terms in insulating materials.