Insulating Liquids in electrotechnology - Applications and perspectives

Insulating liquids have been used from the very beginning of the development of high-voltage electrical equipment. In general, liquids are associated with solid insulators, and their main role is to replace air in the cavities of solid insulators to improve resistance to partial discharges and dielectric breakdown of the insulation. In some cases, notably in power and distribution transformers, the insulating liquid is primarily a heat-transfer fluid, used to evacuate the heat generated in the core of the device. It is also a practical means of routinely assessing equipment over its lifetime. Indeed, the fluid plays a vital role and (like blood in the body of a living being) enables the condition of the equipment to be diagnosed.

Until the late 1960s, insulating liquids posed no environmental or toxicity problems. The discovery of worldwide pollution by polychlorinated biphenyls (PCBs) brought the entire insulating fluid family under the spotlight, and it became a media target. Since then, most PCB-filled equipment has been retrofilled or replaced by PCB-free fluids. Driven by the search for less environmentally damaging liquids, researchers and engineers have since proposed a variety of synthetic/natural or plant-based liquids for electrical engineering applications. The Paris climate agreement, signed by 194 parties (193 countries plus the European Union), covering the mitigation and adaptation of greenhouse gas emissions and the divestment of fossil fuels, is another structuring element that has stimulated the exponential development of new technologies based on biodegradable materials. From now on, the focus will be on harvesting resources that are more efficient, more respectful or less damaging to the environment.

Nanotechnology, seen as a panacea for various engineering problems, is another focus of interest that has driven the development of nanoliquids in recent decades.

Developments in superconductivity have also sparked new interest in cryogenic liquids and liquefied gases.