Hubbell Power Systems Blog

Brief History of Materials Used in High Voltage Insulator Construction

As the power grid continued its expansion in the latter part of the 19^th century, it became even more critical to safely and effectively insulate the high voltage lines from its surroundings. Telegraph lines had been supported primarily by glass insulators for decades, but these same glass insulators weren’t sufficient for high voltage power lines. Similar in its ceramic nature, but more durable in its construction, porcelain became the primary material for high voltage insulator construction.

TDG or thermal diffusion galvanizing is a method of applying a uniform, sacrificial, zinc and iron alloy coating using a metallurgical vapor diffusion process. Hubbell Power Systems, Inc. has investigated this method for use in the coating of end fittings for distribution insulators and the results show improved performance over traditional hot dipped galvanizing (HDG). In addition to improved anti-corrosive performance, TDG is a more environmentally friendly process due to its virtually zero-waste system.

Testing the Thermal Diffusion Galvanizing or TDG Method

Governing insulator standards ANSI C29, as of now, do not define standard prototype or quality conformance tests due to a change in galvanizing method. Because of this, Hubbell Power Systems treated the TDG end fittings as a different material and went through the prototype test requirements per the relevant insulator standards. In addition, samples were tested in a salt fog chamber according to ASTM B117 and mechanical testing of effective crimp trials were conducted to ensure process capability.

For change of metal end fitting materials in polymer distribution suspension insulators, also known as PDIs, the following prototype tests were required per ANSI C29.13:

• Water Penetration Test
• Power Arc Test
• Tensile Load Test
• Torsional Load Test
• Thermal Mechanical Test

Testing was completed primarily at the ISO 17025 accredited Hubbell Power Systems high voltage test facility in Wadsworth, OH and all testing passed successfully.

The anti-corrosion performance of the samples from the ASTM B117 salt fog chamber located in our Centralia, MO lab is shown below by comparing standard HDG end fittings and TDG end fittings. After 4,000 hours of salt fog exposure, the HDG samples are thoroughly covered with deep penetrating corrosion, while the TDG samples show corrosion only in limited areas with minimal penetration. 

The Insulators Business Unit at Hubbell Power Systems, Inc. strives to provide innovative solutions to the changing needs of our customers. In our effort to provide a complete line of products that deliver strength and quality, we are excited to announce the development and launch of our new product, the MITY-Lite® Line Post Insulator. The MITY-Lite joins the already existing 69kV Veri*Lite™ Line Post product line that our customers are familiar with and depend on. 

In physics, the glow and audible event occurring when an insulator is exposed to excessive voltages is called a corona. It may also be known in the electric industry as “corona discharge,” “plume discharge,” “brush discharge” or “glow discharge.”

To support design and development activities, we maintain a fully equipped electrical and mechanical test facility with the capability of performing virtually all of the industry required tests, including ANSI, IEC and CSA. 

Toughened glass bell insulators are easily identified through the application of color bands on the caps, signifying the most common strength class products. 

When designing a high voltage transmission line utilizing toughened glass bell insulators, engineers must consider whether or not to specify a zinc sleeve to accompany the insulator pins. Although the upfront cost is slightly more than the forged steel pin, those who are new to the use of toughened glass bells may ask what justifies a slightly higher expense for the addition of this feature.