Materials innovations improve energy efficiencies

New generation epoxy systems that combine unprecedented durability and easy processing improve the reliability and longevity of energy generation and distribution equipment including wind blades, high-voltage insulators and composite-reinforced conductor cables.

In 2009, the American Society of Civil Engineers (ASCE) evaluated the condition of the U.S. infrastructure and awarded it an overall "grade" of "D" with little to no improvement since the group's 2005 report. The energy sector was distinguished by moving from a "D" to "D+" because the power grid has received some reinforcement and continued investment is expected in generation, transmission, and distribution before 2030.¹

Electric utilities and their suppliers are keenly aware of the enormous need for improvement and are working together to meet that demand. Accompanying the new technologies being developed by utilities are significant developments in the materials electrical engineers use to design and manufacture higher performing equipment. New generation epoxy systems from companies like Huntsman are, for example, leading the way to increased reliability and extended operating service life in parts ranging from wind blades to medium-voltage transformers, high-voltage insulators and lightweight conductor cables. Each application presents its own unique set of challenges for materials formulators who are called on to create cost-effective systems that satisfy specific manufacturer processing and performance criteria.

Nanotechnology

To support the production of ever-larger wind turbines for power generation, Huntsman is applying nanotechnologies used for aerospace materials to formulating super tough epoxy adhesives for fabricating rotor blades. The requirements are extraordinary. Blades, which can have tip speeds of more than 200 miles per hour, are exposed to temperature and weather extremes as well as multi-directional shear and flexural stresses. Service life for each blade is expected to be more than 20 years.

To withstand these conditions, new methods for toughening the epoxy adhesive used in assembling blades are yielding impressive improvements in bonding quality to reduce skin/adhesive delamination and adhesive joint failure. Specifically, by utilizing nanoparticles during polymerization, Huntsman chemists are dramatically increasing crack resistance and crack propagation in wind blade adhesives (Fig. 1). Nanoparticles are also characterized by a much lower density than traditional mineral or fiber reinforcements to produce adhesives that contribute to significantly reduced finished part weight. The result: major savings are realized in the cost of transporting large rotors to the installation site.

Figure 1: Properties of Advanced Epoxy Adhesive vs. Nano-toughened Epoxy

	Advanced epoxy adhesive	Nanoparticle toughened adhesive
Single lap shear strength on laminate (MPa)	26	28
Crack initiation resistance Bend notch K1c (MPaÖm)	1.3	2.4
Crack propagation resistance Bend notch G1c (J/m2)	375	1625

Furthermore, dynamic testing demonstrates that the newly developed nanoparticle-based adhesive is four times more fatigue-resistant than advanced epoxy adhesive. For wind blade manufacturers, this capability translates to substantial longevity of the blades.

Fig. Nano-toughened epoxy adhesive produces wind blades with extended longevity.

Epoxy Casting Systems

For many years, high-performance cycloaliphatic epoxies have been used to mold durable, weather-resistant bushings, insulators and transformers used in substations. Today, utilities and their suppliers are using next generation epoxies to cast one-piece insulators capable of withstanding exposure high transmission line voltages as well as medium distribution line voltages. When compared with conventional oil-impregnated paper (OIP) and resin-impregnated (RIP) porcelain bushings, the advanced cycloaliphatic epoxy units maintain high-dielectric and mechanical strength even when exposed to temperature variations, UV light and corrosive environments. As a result, solid-cast bushings offer extended service life to cut costs, representing major economies to utilities that rely on hundreds of bushings in each substation to distribute power to consumers.

The ease of processing of resilient epoxy systems, and their combination of outstanding arc and track resistance, excellent mechanical and electrical properties and high heat resistance, also makes them ideal for molding components for the Smart Grid. One innovative alternative to conventional circuit reclosers, known as the IntelliRupter® PulseCloser, allows utilities to cost effectively and continuously monitor voltages and currents on overhead power lines. The new equipment from S&C Electric applies very fast, low-energy pulses to the power line. If a short circuit event occurs, such as a lightning strike or tree limb hitting the line, the unit detects the resulting high currents and interrupts the fault without producing system-damaging stresses or voltage sags. The field-proven device minimizes the need for repair crews to respond to all fault situations and reduces the incidence of blown fuses that require replacement by utility crews.

Fig. Hydrophobic Araldite® S-HCEP epoxy increases durability in composite insulators

Huntsman has also recently produced a semi-flexible, cycloaliphatic epoxy for producing sheds on reinforced fiber-core composite insulators used in medium- to high-voltage outdoor power applications. Known as Araldite® S-HCEP (Shed Hydrophobic Cycloaliphatic Epoxy) material, the new product exhibits intrinsic hydrophobicity, hydrophobicity transfer and recovery. It is designed to absorb the stresses that occur in composite insulators to increase durability. It is also formulated to provide good tracking and erosion resistance as well as good water diffusion breakdown strength. In addition to outstanding performance, the cost-effective new product is easy to handle to reduce processing costs.

Reinforced Epoxy Composites

Pultruded carbon and glass-reinforced epoxy cores overwrapped with conductive annealed aluminum wire are providing the utility industry with a new technology in high strength/light weight and corrosion-resistant electrical conductor cables. The high-temperature, multi-functional epoxies used for this application support the fabrication of high tension cables that operate at higher current levels with more than 20% higher current-carrying capacity and virtually no eddy current losses compared with conventional steel cables. Because of the composite cables have only 10 percent of the sag that characterizes all-steel conductor cables, they can accommodate longer spans between towers, reducing the number of towers required to carry an electrical load by as much as 16 percent. As a result, utilities that opt to install the composite cables are reducing overall project costs by three or four times.²

Summary

Today, congested transmission paths produce power outages and power quality disturbances that cost the economy between $25 billion and $180 billion annually, making equipment improvements a necessity.³  Given the growing need of utilities to improve the performance reliability of existing equipment and upgrade the generation and distribution capabilities of new programs, materials advances are more important than ever before. Suppliers like Huntsman are working in partnership with equipment manufacturers and utility engineers to ensure that the specially developed epoxy systems available to them for bonding, molding and composites fabrication meet or exceed stringent requirements to support upgrades in all aspects of the energy market sector.

Araldite is a registered trademark of Huntsman Corporation or an affiliate thereof in one or more, but not all, countries.

IntelliRupter is a registered trademark of S&C Electric Company.

DISCLAIMER:

All information contained herein is provided "as is" without any warranties, express or implied, and under no circumstances shall the authors or Huntsman be liable for any damages of any nature whatsoever resulting from the use or reliance upon such information.

Footnotes:

¹ Amanda Hurley, "ASCE Issues Report Card on U.S. Infrastructure", Architect, 9 Feb 2009, http://www.architectmagazine.com/design/asce-issues-report-card-on-us-infrastructure.aspx

² Donna Dawson, "Composites Connect With the World of Cabling", Composites Technology, 1 Feb 2006, http://www.compositesworld.com/articles/composites-connect-with-the-world-of-cabling.aspx

³ U.S. Energy Department, Office of Electricity Delivery and Energy Reliability, 2009 Congestion Study, http://www.congestion09.anl.gov/involve/searchcomment/index.cfm