Thermal properties of dielectric materials:, Physics

One of the functions of the insulation is hest transfer. Consider an underground cable under operation. This cable is recommended for operations. This cable is recommended for operation with certain limitations of voltage and current. Suppose if the voltage is increased insulating material is able to withstand the higher voltage stress, the voltage will cause increase of dielectric loss that will increase heat generation. Ultimately the temperature of the insulating will further increase. If the insulator starts losing its insulating properties, ultimately breakdown will occur. Secondly if the load current in the cable is increased, P losses will increase, resulting once again in increased heat generation and failure as mentioned. Temperature affects such diverse and important properties as electrical properties, mechanical strength, hardness, viscosity, solubility etc. This makes thermal properties more important. It will now be appreciated why a complete classification of insulating materials on their operating temperature has been done. Various thermal properties are discussed below.

 

(1)       Melting point: It assumes importance in specific cases like non draining compound, impregnated paper, insulated cable etc. It is desired in the entire of operating temperature range of cables the impregnating compound must not melt avoid to migration of oil.

 

(2)         Flash Point: It will impose restriction in manufacturing process to avoid possible hazard of apparatus catching fire.

(3)         Volatility: IT assumes importance from the fact that when a trapped gas is evolved from a volatile insulating material subjected to voltage stress. The breakdown is very rapid. A volatile material cannot be a good insulator.

(4)        Thermal conductivity: Heat generated due to power losses and dielectric losses will be dissipated through the insulator itself. However effectively this flow of heat takes place, depends on the thermal conductivity of the insulator. An insulator with better thermal conductivity will not allow temperature rise because of heat transfer through it to the from the

 Atoms sphere. This property assumes great importance in high voltage apparatus where thickness of insulation is more.

Thermal expansion: An insulator with a high coefficient of expansion poses problems. Repeated load cycles of an apparatus cause corresponding and contraction of the insulator leading to the possibility of the formation of voids in it. When there are insulating materials involved to form insulation system different coefficients of expansion of the two will further increase the formation of voids. These voids have been found to be the major causes of insulation breakdown. Be it understood that thermal expansion is of significant importance where heavy currents are involved. In communication and electronic system this obviously is not significant.

(5)        Heat Resistance: This is a general property which desires that a dielectric should withstand temperature variations within desirable limit, without damaging its other important properties .If an insulator has favourable properties at ambient temperature but it not able to retain these properties to desirable extent at higher temperatures but is not able to which it has to operate, it is not good insulator. On the contrary an insulation which is capable of withstanding higher temperatures up to which it has to operate. This means that the current loading can be increased. This making apparatus capable of handling more power. This favours economy.

Posted Date: 7/7/2012 5:57:41 AM | Location : United States







Related Discussions:- Thermal properties of dielectric materials:, Assignment Help, Ask Question on Thermal properties of dielectric materials:, Get Answer, Expert's Help, Thermal properties of dielectric materials: Discussions

Write discussion on Thermal properties of dielectric materials:
Your posts are moderated
Related Questions
Understand the manufacturing technique of optical fibres by using chemical vapour deposition method. A Traversing oxy-hydrogen flame heats the reaction zone to a temperature ar

A vertical spring generates simple harmonic motion with period 1sec. when a mass of 1gm suspended at the lower end of the spring, calculate the length through which the spring stre

A ray of light falls on a glass slab of refractive index u.if the reflected and refracted rays are mutually perpendicular to each other,find the angle of incidence. Ans) let i b

Presbyopia: The accommodation power of a person is lost by which the suffers a long sightedness. It is known as Presbyopia or lack of accommodation.

Erika is on an elevator and presses the button to go down. When the elevator first begins moving, it has an acceleration of 2.5 m/s 2 downward. Erika and the elevator have


A thermal imager is used to measure the temperature of a target surface (ε = 1) in the test section of a wind tunnel. The thermal imager must view the target though a window. The t

A toy car with a mass of 0.75 kg is pulled3.2 m across the floor with a constant force of 110 N. If 67 J of work is done, what is the upward angle of the force?

What are intrinsic and extrinsic semiconductors? A semiconductor is a material that has an electrical conductivity among that of a conductor and an insulator. In a semiconducto

Atwood's machine A weight-and-pulley system is used to measure the acceleration because of gravity at Earth's surface through measuring the net acceleration of a set of weight