Looking up at transmission towers, insulators are easily overlooked. A closer look reveals that while both are suspended between the conductors and the tower, some are translucent, while others have a white ceramic texture. Why haven't the power grid uniformly switched to just one material after so many years of use? The reasons are related to the timing of power grid construction, line conditions, and equipment status.
Why have ceramic insulators been used for so many years?
Ceramic insulators entered the power system very early. In the early construction of transmission lines, ceramic materials already had relatively mature manufacturing processes, exhibiting good performance in insulation, mechanical strength, and outdoor weather resistance.
Transmission lines are erected outdoors for extended periods, enduring rain, wind, sun, and temperature fluctuations. Ceramic materials can maintain relatively stable performance in such environments, hence the widespread use of ceramic insulators in many previously constructed lines.
Many of these lines are still in operation today, and some insulators remain in good working order. As long as their insulation and mechanical properties meet operational requirements after testing, they can continue to serve.
What's the difference with glass insulators?
The widespread use of glass insulators later became related to the increase in transmission voltage and changes in line maintenance requirements. A key advantage of tempered glass insulators is their ease of visual identification of fault conditions. When a tempered glass insulator experiences a breakdown, the shed disc may spontaneously shatter, breaking the glass body, making the anomaly easily visible to inspectors. Transmission lines are long and involve numerous towers. If the fault location can be directly identified visually during inspections, the workload is significantly reduced. This is one reason why glass insulators are widely used in high-voltage transmission lines.
Of course, insulator selection cannot be based solely on material. Factors such as line voltage level, mechanical load, pollution levels, and climate all influence the specific selection.
Why not replace all normally functioning ceramic insulators?
A transmission line can span tens to hundreds of kilometers, traversing mountainous areas, farmland, rivers, and urban regions. Removing all normally functioning ceramic insulators and installing new glass insulators would involve not only material costs but also transportation, construction, maintenance, and power outage arrangements. For equipment in good condition, the investment in this approach does not match the actual benefits. Power grid equipment upgrades are typically carried out gradually, following line modifications, equipment status assessments, and maintenance plans. Equipment requiring replacement is addressed promptly, while equipment meeting operational requirements continues to be used. This approach aligns better with the operational characteristics of large-scale power infrastructure.
Which type of insulator is better?
It's difficult to answer in a single sentence. Ceramic insulators are technologically mature, have extensive operational experience, and remain valuable in many existing lines. Glass insulators offer advantages such as easier fault identification and are used in many newly built and upgraded lines. Actual engineering projects must also consider factors such as voltage level, line structure, environmental conditions, pollution levels, icing, and mechanical loads. Insulator selection is not simply based on "new" or "old."
Therefore, the presence of "one glass and one ceramic" insulators on transmission towers does not necessarily indicate a delay in equipment upgrades. It's more like a timeline of power grid construction: equipment from different eras continues to perform its respective tasks as long as it meets operational requirements, while lines requiring upgrades are gradually upgraded according to maintenance and construction plans.
For a vast power grid, this planned upgrade approach is more practical than large-scale replacements for the sake of uniformity.
