Insulating Surge Arresters with Metal Oxide Varistors (MOV)

The primary defense to protect electrical equipment from over-voltages is surge arresters. These necessary devices hold metal oxide varistors (MOVs) and are rapid response protectors against voltage spikes. Effective insulation is needed on the outside surfaces to ensure optimal performance and safety of the MOVs.

Power line connected to a surge arrester. Image Credit: iStock.

This article explains the unique value of glass as a suitable insulation material for this purpose. Its advantages are explored, and some considerations are detailed for the implementation of glass coatings in surge arresters.

Understanding the Need for Insulation in Metal Oxide Varistors

Metal oxide varistors are discs made primarily from zinc oxide crystals. This type of polycrystalline semiconductor ceramic demonstrates nonlinear volt-ampere properties. When subjected to high voltages, this feature allows MOVs to conduct strongly and divert excessive currents away from sensitive equipment. Proper insulation is vital in preventing inadvertent electrical pathways and guaranteeing dependable operation. This highlights the significance of glass coatings in MOVs.^1,2,3

Glass’ exceptional insulating capabilities make it an ideal choice for encasing MOVs within surge arresters. The inherent physical and chemical qualities of glass provide electrical insulation, thermal stability, and mechanical robustness. These features are vital to its performance in demanding operating environments .⁴

The Electrical and Dielectric Advantages of Glass Coatings

A primary benefit of using glass in this application is its extraordinary dielectric strength, greater than certain ceramics.

Glass coatings can resist strong electric fields without degrading effectively isolating MOVs from outside electrical interference, which minimizes the possibility of short circuits or leakage currents. The longevity and dependability of surge arresters are guaranteed by dielectric resilience, which is vital for protecting sensitive electrical equipment.^5,6

If the conditions during manufacturing are not controlled, adhesion between the glass coating and the MOV disk can be poor, and the disk surface can deteriorate due to exposure.

Transverse fields caused by substantial external pollution can lead to internal partial discharges in porcelain-housed arresters. Certain polymeric coatings can be damaged by these discharges triggering the creation of corrosive gases. Polymeric coatings have been noted as less likely to prevent discharge damage to the disk surface when compared to glass coatings.⁷

Thermal stability: Enhancing performance with glass insulation

Due to its extraordinary thermal stability, glass can tolerate elevated temperatures without degrading. The thermal resilience of glass coatings is valuable for surge arresters, which prevent overheating and maintain performance with rapid heat dissipation. Glass insulation increases the operational lifespan of MOVs by effectively discharging heat and providing long-term protection from voltage surges.

The thermal expansion coefficient of glass insulators is matched to MOV substrates by design. This results in nominal comparative deformation even with fluctuations in temperature. In response to thermal shock, glass insulators can shatter rather than crack. This underrated benefit of glass makes detecting defects easier than materials that fail with no obvious physical change.⁵

Mechanical durability: Protecting MOVs in challenging environments

The structural strength of surge arresters is reinforced by the mechanical longevity of glass. It provides protection from environmental factors like moisture, vibration, and mechanical stress. Glass has greater resistance to damage and mechanical compressive strength that is 1.5 times higher than ceramics. In outdoor applications, surge arresters’ exposure to extreme environmental conditions and mechanical impacts makes the durability of glass vital.⁵

Versatility in Design and Manufacturing Processes

The electrical, thermal, and mechanical properties of glass enable precise customization for various surge arrester designs, providing versatility to the manufacturing process.

Glass powders can be customized for wet applications like dipping, rolling, or spraying, as well as dry electrostatic techniques. Powders can be accurately refined to meet specific particle size requirements. They can be mixed with additives to improve surface textures for easier handling. Glass insulation can contain lead or be lead-free, and can be easily dyed in a multitude of colors to meet the requirements of an application.⁸

Considerations for Implementing Glass Coatings in Surge Arresters

Using glass coatings in MOVs for surge arresters requires thoroughly investigating material compatibility, manufacturing processes, and cost-effectiveness regardless of its known advantages.

Although glass offers superior performance, implementing it requires proficiency in materials engineering and specialized manufacturing fabrication methods. In addition, cost and supply chain dynamics could impact the viability of including glass insulation in surge protection systems.

Advancing Surge Protection Technology with Glass Insulation

Glass is an exceptional insulator for metal oxide varistors in surge arresters, providing extraordinary electrical, thermal, and mechanical attributes. The dielectric strength, thermal stability, and mechanical durability make glass valuable in protecting electrical systems from voltage surges.

The challenges of manufacturing complexity and cost are outweighed by the benefits of glass insulation compared to alternative materials. This reaffirms glass insulation’s position as a cornerstone in surge protection technology.

To learn more about the applicability of glass as a coating and investigate the various specialty glass coatings available, contact the Mo-Sci team today.

References and Further Reading

1. Meshkatoddini, M.R. (2011). Metal Oxide ZnO-Based Varistor Ceramics. Advances in Ceramics – Electric and Magnetic Ceramics, Bioceramics, Ceramics and Environment. doi.org/10.5772/23601
2. Yutthagowith, P., et al. (2021). A Simplified Model of a Surge Arrester and Its Application in Residual Voltage Tests. Energies. doi.org/10.3390/en14113132
3. Meng, P., et al. (2020). Excellent electrical properties of zinc-oxide varistors by tailoring sintering process for optimizing line-arrester configuration. ICHVE. doi.org/10.1109/ICHVE49031.2020.9279439
4. Saleem, M.Z., et al. (2022). Review of the Performance of High-Voltage Composite Insulators. Polymers. doi.org/10.3390/polym14030431
5. Taherian, R. (2019). Advantages and Disadvantages of Glass Insulators. In: Electrical Conductivity in Polymer-Based Composites.
6. Su, T.Y., et al. (2023). Modelling and analysis of electrical performance outdoor glass insulator under various services and lightning impulse. Journal of Physics: Conference Series. doi.org/10.1088/1742-6596/2550/1/0120201
7. INMR. (2018). [Online] Quality of Metal Oxide Disks Impacts Surge Arrester Performance. Available at: https://www.inmr.com/quality-metal-oxide-disks-impacts-arrester-performanc/ (Accessed on 29 March 2024).
8. 3M Advanced Materials Division. (2015). 3M™ Specialty Glass for Metal Oxide Varistors. Available at: https://studylib.net/doc/18476855/3m%E2%84%A2-specialty-glass-for-metal-oxide-varistors-data-sheet (Accessed on 29 March 2024). 

This information has been sourced, reviewed and adapted from materials provided by Mo-Sci.

For more information on this source, please visit Mo-Sci.