Selection Requirements for Glass Fibers in Taporel Insulating Core Rods

1. The Dominant Role of Glass Fiber

Glass fiber is the primary structural material in insulating core rods, serving as the reinforcing “skeleton.” In composite insulators used domestically, glass fiber accounts for approximately 80% of the core rod’s total weight and about 65% of its volume. Consequently, the properties of the glass fiber dictate the overall performance of the core rod.

2. Advantages of E-Glass (Alkali-Free Glass Fiber)

Composite insulator core rods typically utilize E-glass (Alkali-free glass fiber). E-glass is primarily composed of silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), and boron oxide (B₂O₃). These oxides possess stable molecular structures and exist in a crystalline phase that provides exceptional insulation.

• The “Neutralization Effect”: Trace amounts of potassium oxide (K₂O) and sodium oxide (Na₂O) are unavoidable impurities. These alkali metal oxides tend to exist as ions, which can be detrimental to insulation. However, by maintaining a specific concentration ratio between potassium and sodium ions, a “Neutralization Effect” is achieved, significantly reducing their impact on the material’s dielectric properties.

• The “Suppression Effect”: The presence of calcium oxide (CaO) and magnesium oxide (MgO) in E-glass promotes a denser crystalline structure. These alkaline earth metal oxides create a “Suppression Effect” that obstructs the pathways of alkali metal ions, further enhancing the material’s resistivity.

Due to these combined effects, the E-glass used in our core rods exhibits high resistivity and superior insulating performance.

3. Trade-offs with Acid-Resistant Glass Fibers

While acid-resistant glass fibers exist, their mechanism for resisting acid and water corrosion requires a reduction in the content of alkaline earth metal oxides. Unfortunately, this inevitably disrupts the “Neutralization and Suppression Effects” found in E-glass. This disruption causes a non-linear, sharp increase in the fiber’s electrical conductivity, thereby degrading its insulating properties.

4. Comparative Experimental Data

Tests conducted on acid-resistant glass fiber core rods from international sources revealed significant differences when compared to E-glass core rods:

• Boiling Test: The leakage current of acid-resistant rods was nearly 10 times higher than that of E-glass rods.

• DC Leakage Test: Under a 6kV DC voltage applied across a 10mm specimen, the DC leakage current of the acid-resistant rod was more than 4 times greater than that of the E-glass rod under identical conditions.

• Ion Migration Test: During a 100-hour ion migration test at 140°C with 6kV DC, the leakage current of the acid-resistant rod changed by nearly two orders of magnitude. In contrast, the E-glass rod’s leakage current only increased by approximately 1.5 times under the same conditions.

5. Conclusion

Although acid-resistant fibers offer better chemical durability, they suffer from high conductive current. For composite insulator core rods that must continuously withstand both high voltage and mechanical tension, this is a critical disadvantage. The phenomenon of ion migration under DC electric fields is particularly damaging to the performance of acid-resistant fibers.

Therefore, to ensure maximum electrical reliability and long-term stability, composite insulators should utilize E-glass (Alkali-free) core rods.