|
November 2007 |
||||
| Contact Angle and High-Voltage Power Transmission | ||||
|
C. Roero1 and others have shown
how contact angle can be used to characterize the materials and various
surface treatments used on high-voltage transmission lines. One of the problems
to solve is understanding how to reduce "wet noise" caused after periods
of precipitation. This hum is caused by the fixed frequency (120Hz in
USA) of the electricity and the water droplets that remain on the lines
and insulators. By exposing sessile drops to an electric field,
researchers are able to better understand the efficacy of hydrophobic
coatings and materials designed to reduce this nuisance and improve the efficiency of
transmission. Understanding the surface treatments can help material
scientists develop or improve products that will eject the water or
otherwise minimize the undesirable side effects. The problem of "wet noise" was first studied in the late 1960s by E. R. Taylor, et al2. More recent studies employing contact angle measurements take the earlier work of answering the "what" to newer levels of understanding by answering the "why" and "how to fix" this condition. The early studies showed how water droplets in an electrical field would deform and how strong field strengths could result in a loss of charge and the emission of undesirables sound. More recent work shows how a hydrophilic surface, for instance, produces smaller droplets with low contact angles. These types of drops deform less and thus lower the level of noise during the half hour drying period which follows rainfall. The other variable studied is the speed of evaporation and how it might be accelerated by using specific materials or surface treatments. It was determined that the factors that affect overall noise and speed of evaporation are: the drop size, the surface condition, and the relative field strength. As the field strength is increased, the drops become more pointed but flatter at the base resulting in a decrease in contact angle. Roero showed also that for 50μL to 100μL-sized drops, as the contact angle decreased from 90° to about 10°, the instability voltage (aka, voltage collapse) roughly doubled. For smaller drops the increase in voltage collapse was closer to 200%. The result of these studies is a number of new and innovative materials. One such material3 developed and marketed by Tyco Electronics is an insulation product made from a polymeric material (developed by Raychem) with an additive of flourine-substituted compounds results in a material with greatly higher hydrophobicity. Another material developed by GE4 consists of a silicone polymer and in inorganic hydrophobicity imparting particulate (HIP). These particulates can be found in layered silicate minerals such as kaolinite, halloysite, montmorillonite, vermiculite, and others, as well as three-dimensional silicates such as feldspars, zeolites, ultramarines. In short, extensive underlying research -- including contact angle measurements of sessile drops -- has and continues to allow researchers and scientist to characterize materials and surface treatments used in the transmission of high-voltage current. Such research has led to numerous innovative products and materials that both increase the efficiency of transmission systems by reducing voltage collapse and reducing undesirable noise thus increasing the quality of life for those that live near power transmission lines. 1 Contact Angle, Wettability
and Adhesion, Vol. 4, pp. 165-176, Ed. K. L. Mittal. This paper is
available here:
http://www.eeh.ee.ethz.ch/downloads/hvl/publications/roero_Contact_angle_ |
||||
| End of Year Sales Planning | ||||
|
We typically receive a number of orders in December which must be delivered before the end of the year in order to meet end-of-year fiscal and calendar year purchasing requirements. While we appreciate all orders, often it becomes particularly challenging trying to meet unrealistic deadlines. While we will do everything in our power to facilitate our customers' requirements, there are some delivery requirements that we are not able to guarantee. Thus, if you are considering the purchase of complete goniometer system or accessory that needs to be delivered and invoiced before the end of the year, we would encourage you to expedite your purchase order. Most of our instruments have a 3-4 week lead time and some of our accessories may lengthen delivery.
|
||||
