Polymer compounds suitable for electrical insulation can consist of 10 or more ingredients which can be broken down to three major categories. These include the base polymer, fillers which can make up nearly 50% of the total compound, and active additives. Compounding of an elastomer with fillers and additives to achieve the desired results for a given application is critical. The components are carefully selected to enhance field performance and ease of manufacture.
After defining the characteristics required of an ideal polymer (link to first blog) housing material, the next step is to develop an appropriate test protocol. Good polymer compounds (link to 2nd blog) used for high voltage insulation should be tested for the ability to resist tracking, erosion, corona, and ultra-violet (UV) radiation exposure to ensure long term reliability. The section below provides a high-level overview of the key test procedures defined to achieve the previously mentioned characteristics. The testing regime, outlined in Table 1, allows various materials to be evaluated and led to the optimum material selection for electrical insulation applications.
It’s a commonly held belief that the single most important characteristic for insulating materials is hydrophobicity, the ability to shed water or cause water films to bead, breaking up the potential leakage current path. Because the polymer housing is the primary defense for system critical distribution equipment, there are several other important polymer characteristics worth taking into consideration.
Prior to 2009, ASTM F855, Standard Specifications for Temporary Protective Grounds to Be Used on De-energized Electric Power Lines and Equipment only included one table indicating the specifics to which ground set designs were to be tested. This “Table 1” was based on a near symmetrical current, limiting the circuit inductive reactance to resistance (X/R) ratio to a maximum of approximately 1.8 (20% asymmetry).
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 o
nly in limited areas with minimal penetration.
Electric Utility Engineers who design and maintain transmission lines face many challenges including weak, soft soils that can’t bear much weight and aggressive soil that corrodes metal. Whether you are facing Virginia’s Coastal Plain or western Colorado’s Mancos Shale, CHANCE® offers protection to ensure the helical foundations and anchors beneath transmission towers will function properly and withstand the test of time.
Distribution lines can face harsh conditions. If standard products aren’t doing the job and you need more protection for your standoff brackets and guy strains, look no further. Here are four reasons to switch to silicone-coated fiberglass construction products:
It is well-documented that the best method for predicting the capacity of helical piles and anchors is to measure the installation torque. Accurate torque measurements are crucial to calculate the load capacity or holding capacity.
It’s a bittersweet moment to look back on an event like the 36th Annual International Lineman’s Rodeo & Expo and to realize that for all the preparation and hard work, the event is done. The best linemen in the world brought their best to compete, and, for the rest of us, we watched and admired their skill, speed, and strength.
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.