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The electrical breakdown of an insulator due to excessive voltage can occur in one of two ways: A puncture arc is a breakdown and conduction of the material of the insulator, causing an electric arc through the interior of the insulator. The heat resulting from the arc usually damages the insulator irreparably.
Thermal conductivity depends on the material and for fluids, its temperature and pressure. For comparison purposes, conductivity under standard conditions (20 °C at 1 atm) is commonly used. For some materials, thermal conductivity may also depend upon the direction of heat transfer.
Thermal insulators are materials that inhibit the migration of heat. For electrical insulators, materials that inhibit the migration of electric current, ...
However, the general correlation between electrical and thermal conductance does not hold for other materials, due to the increased importance of phonon carriers for heat in non-metals. Highly electrically conductive silver is less thermally conductive than diamond , which is an electrical insulator but conducts heat via phonons due to its ...
These thermal greases have low electrical conductivity and their volume resistivities are 1.5⋅10 15, 1.8⋅10 11, and 9.9⋅10 9 Ω⋅cm for 860, 8616 and 8617 respectively. The thermal grease 860 is a silicone oil with a Zinc Oxide filler and 8616 and 8617 are synthetic oils with various fillers including Aluminum Oxide and Boron Nitride.
Electrical machines are usually designed with an average temperature below the rated hot-spot temperature to allow for acceptable life. Insulation does not suddenly fail if the hot-spot temperature is reached, but useful operating life declines rapidly; a rule of thumb is a halving of life for every 10 °C temperature increase.
This is a list of insulation materials used around the world.. Typical R-values are given for various materials and structures as approximations based on the average of available figures and are sorted by lowest value.
Bulk insulators block conductive heat transfer and convective flow either into or out of a building. Air is a very poor conductor of heat and therefore makes a good insulator. Insulation to resist conductive heat transfer uses air spaces between fibers, inside foam or plastic bubbles and in building cavities like the attic.