No insulating material has an unlimited lifespan and the dielectric properties can degrade over time. Although the deterioration factors for these insulators may vary, the consequences are always the same: failure of the equipment to be protected. It is therefore essential to always choose the material adapted to the specifications.
Two factors mainly come into play in the deterioration of the dielectric properties of insulators:
Indeed, throughout its life, the electrical insulator is brought to fight against the current. This permanent fight weakens it, because the electric current gradually erodes the surface of this insulator. After a certain time, an electric arc appears and therefore the insulation function breaks .
Furthermore, the more violent the attack of the current, and therefore the higher the voltage, the faster this degradation.
Apart from these factors whose impact is systematic, there are many other deterioration parameters to take into account. These are linked to the environment in which the insulation evolves and can be linked to various physico-chemical processes:
Concretely, the degradation of a material leads to a deterioration of the insulating properties, ie to a reduction in the dielectric strength.
The material will therefore become less resistant to the effects of the electric field and there is then a risk of breaking the dielectric function.
The consequences of a break in the dielectric function of the material are unfortunately often irremediable. In fact, when this occurs following a partial discharge, the insulation is destroyed and the electrical equipment it must protect immediately ceases to operate. To illustrate, we can therefore say that the electrical insulator behaves like “the fuse of the insulating function”.
Anticipating this deterioration is not always easy, because the degradation of the insulation itself is not visible before it breaks. This is why it is important to choose quality materials that are adapted to the actual conditions of use. Here are 2 essential criteria to take into account:
It is essential to know precisely the functional constraints of the equipment to be protected, whether it is a rotating machine or a transformer, so as to choose the insulating material which will best correspond to the specifications.
The choice of insulation is thus guided by its dielectric performance but also by its thermal class , which is why European standards such as IEC and UL certifications play an important role.
Concerning the service life of the insulator, it is known that the dielectric strength varies according to the ranges of insulating materials chosen. The deterioration of a poor quality insulating material may thus occur prematurely due to defects, such as cavities present in the material.
Thus, choosing materials from recognized manufacturers is always advisable , because manufacturers engage in a certification process which often guarantees better resistance to the degradation of dielectric properties.
During its life, an insulating material is subjected to intense electrical and thermal stress which weakens it and degrades its dielectric properties. If the deterioration of an insulator is unavoidable, it can be limited by choosing quality materials and adapted to the real operating conditions .
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