Before writing this article, after seeing those towering transmission towers, I couldn't help but feel delighted by these power facilities. At the same time, a question arose in my mind: With so many conductors transmitting enormous amounts of electrical energy day and night, how can we ensure that these high-voltage lines do not harm people around them? This is closely related to a key device: the insulator. Insulators play a critical role in providing insulation for the conductors. In this article, let’s step into the world of insulators.

The first question is: What is the function of an insulator?

As the name suggests, the word "insulator" contains "insulation," so its primary role is to provide insulation, i.e., to suspend conductors and keep them electrically isolated from the tower and the ground. Whether on high-voltage, extra-high-voltage, or ultra-high-voltage lines, insulators are indispensable on overhead lines of any voltage level.

Second, what materials are insulators generally made of?

They can be roughly divided into three types: porcelain insulators, glass insulators, and composite insulators.

The earliest to appear and with the most extensive operational experience is the porcelain insulator, which can be considered an old-timer. It has made great contributions to the development of the power industry. Its characteristic is that it has no hydrophobicity — just the opposite of a lotus leaf. Water droplets do not stay on a lotus leaf, but porcelain insulators do not have this property. Because of this, contaminants on the surface of porcelain insulators become damp and wet under humid weather conditions. To maintain the insulation level of the insulator, power supply workers need to clean the accumulated dust and dirt on its surface to prevent the reduction of external insulation strength and avoid pollution flashover accidents. The maintenance cycle is about 5 to 8 years.

Next came the glass insulator. As the name implies, it is made of glass, specifically tempered glass. Once it deteriorates, it will self-explode, which can be visually identified by power supply workers. Due to this characteristic, glass insulators do not require deterioration detection. Like porcelain insulators, they also have no hydrophobicity and need cleaning to restore their surface insulation level.

Finally, we have composite insulators. They are mainly made of silicone rubber and rod materials. Unlike the previous two types, composite insulators are characterized by hydrophobicity and the ability to transfer hydrophobicity. A conductive water film does not easily form on the surface of composite insulators, so they have strong resistance to pollution flashover. Under normal operating conditions, composite insulators require almost no special maintenance, which can greatly save labor costs.

Lastly, what types of transmission lines are insulators generally suitable for? Why do insulator strings at the same voltage level in plateau regions have more discs?

Depending on the application, insulator strings are mainly divided into suspension strings, jumper strings, and tension strings. For extra-high-voltage, ultra-high-voltage lines, and DC lines, the majority of tension insulator strings are made of porcelain and glass insulators. In polluted areas, suspension strings and jumper strings are mostly made of composite insulators. In regions with a clean geographical environment, some composite insulators are used, but porcelain and glass insulators remain the main types.

As for plateau or high-altitude areas, the number of discs in an insulator string is greater than that on a transmission line of the same voltage level at low altitude. In high-altitude areas, for the same string length, the voltage withstand capability decreases, so the length of the insulator string must be increased to raise the insulation level.