Ceramic insulators have been in use on power grids for well over a century and have been subjected to extreme temperatures in both cold and hot climates. But now, as climate change continues to accelerate, the severity of weather patterns and droughts are increasing, in the process exposing power lines and insulators to more and more wildfires. Fires on a forest floor can produce temperatures at 800°C while raging fires at tree top height can be as high as 1200°C.
Lightning strikes and flashovers can cause power arcs resulting in temperatures as high as 19,000°C. More moderately elevated temperatures can be caused by proximity to fire, electrostatic precipitators and induced magnetic fields, or even simply by exceeding current ratings. The operating conditions of a power supply utility also play a role since conductors can reach elevated temperatures during line over currents. Similarly, inductors/coils can induce magnetic fields that heat iron parts to between 150 and 200°C.
Insulators are designed to operate within the normal temperature ranges of the equipment they support and it is therefore not expected that they could be exposed to extreme elevated temperatures without some risk of damage. For example, depending on the event and resulting temperature, an insulator’s mechanical and dielectric strength might decrease. As such, utility equipment will need to be inspected to assess any damage and the urgency of replacement. Insulators with serious damage are often easy to inspect and detect, but pinpointing ones with less noticeable damage is more difficult. To better understand the effects of elevated temperature, different elements of an insulator must be reviewed. How each material reacts, construction design and the manner in which the heat is applied will all play a role.
For example, ceramic insulators are made of a combination of different materials, including the ceramic insulation, fixing metal parts, bonding cement, and expansion coatings. While ceramics and iron fittings can withstand temperatures well above normal operating conditions, the bituminous asphalt used for expansion joints begins to melt at 115.5°C. At this point the bitumen will lose some mechanical strength and could potentially liquefy and run out of the hardware. Similarly, Portland cement can lose mechanical strength due to several factors including temperature level, heat rate, duration, type of aggregate, single event versus thermal cycling and whether or not the cement is confined.
Attend the 2022 INMR WORLD CONGRESS in Berlin where porcelain insulator expert, Patrick Maloney, Chief Engineer with PPC Insulators, will outline the key points that must be reviewed on insulators exposed to elevated temperatures. He will also explain how each material reacts based on how the heat was applied as well as its design and construction.