Insulating Liquids in electrical Engineering - Characterization and properties

The internal sizing of electrical equipment installed on electrical power transmission and distribution networks is conditioned, first and foremost, by the performance of the insulation system. Many of these devices use insulating liquids as impregnants for solid insulators (paper and film) and fillers: transformers (power, rectifier, traction, furnace, potential, current, instrumentation, etc.), resistors, inductors, capacitors, cables, bushings, circuit breakers, tap changers, thyristor cooling in power electronics, etc.

Although insulators are produced with the utmost care, the impact of electrical, mechanical and thermal stresses, combined with the aggressiveness of certain chemical compounds, can lead, over a limited or unlimited period of time and with possible repetition, to their gradual degradation in service conditions. Under certain conditions, the insulation system may fail to perform its function, leading to undesirable failures through dielectric breakdown.

As aging networks will be put under increasing strain by ever-increasing demand in the context of the energy transition, it is essential to characterize and diagnose equipment properly. As liquid is the most easily accessible insulator (sometimes without the need to stop the equipment), the identification of chemical tracers capable of indirectly providing precise information on the state of degradation of the equipment is the most widely used technique.

Characterizing or assessing the condition of insulating liquids is therefore crucial to guaranteeing their reliability. The physicochemical and electrical properties of insulating liquids can affect their performance, and accurate characterization can help predict their service life. This characterization enables us to better understand their properties and optimize their use in various applications. It also helps identify potential problems before they lead to equipment failure.