/ Whitepapers

Design and Construction of an Advanced Tracking Wheel for Insulator Materials Testing

Harrison P. Fletcher, Andrew Macdonald, Chris Secord, Mark Lenckowski, Rajkumar Padmawar, Dennis K. Hore

Abstract—This account details the design and construction of a sophisticated tracking wheel for the accelerated aging of polymer insulators by subjecting them to surface contamination and high voltage. Automated control of wet-dry cycles is achieved by means of a computer-controlled lift mechanism that operates in tandem with the rotation. The applied voltage is continuously variable, and can accommodate insulators of mixed lengths. The design incorporates a fail-safe control system that automates the selected test cycle, provides an intuitive user interface, and integrates multiple safety measures. This is achieved by implementing a programmable logic controller with digital and analog inputs and outputs. An associated ladder logic program automates the actuation of electromechanical hardware while also processing the inputs provided from control hardware such as limit switches, optical encoders, variable frequency drives, and sensors. A touch-screen human interface module provides feedback and allows the user a means of input. Programmed fault detection, flood sensors, and a trapped key system increase the level of user safety and provide environmental and infrastructure protection.

Index Terms—polymer insulators, multi-stress testing, rotating wheel, accelerated aging, degradation

Algae Adhesion onto Silicone is Sensitive to Environment-Induced Surface Restructuring

Zhijing Wan, Md. Shafiul Azam, Shea Wyatt, Kaitlyn Ramsay, Jaime L. Korner, Katherine S. Elvira, Rajkumar Padmawar, Diana Varela, and Dennis K. Hore

Abstract – Resistance to algae contamination is an important characteristic of insulators used in over- head power distribution in coastal environments. It is therefore important to understand the parameters governing algae adhesion onto polymer insulator materials such as silicone. Flow- cell based shear experiments were conducted in order to characterize the adhesion strength of algae onto polydimethylsiloxane surfaces, comparing fresh polymer substrates with those that have been soaked in water and saline solutions for one month. Both freshwater algae and a seawater species could withstand considerably less drag force and were therefore more easily removed when the polymer was soaked in salt water. The polymer surface was found to be unaltered in terms of its roughness, contact angle, and lack of water uptake; no macroscopic surface characterization was therefore able to account for the differences in cell adhesion strength resulting from the soaking treatment. Surface-specific nonlinear vibrational spec- troscopy, however, revealed subtle differences in the orientation of surface methyl groups that resulted from the water and saline exposure.

An Automated Image Analysis Platform for the Study of Weakly-Adhered Cells

Zhijing Wan, Ben T. MacVicar, Shea Wyatt, Diana E. Varela, Rajkumar Padmawar, Dennis K. Hore

Abstract – Details of the design and implementation of an open-source platform for studying the adhesion of cells attached to solid substrates are provided. The hardware is based on a laser- cut flow channel connected to a programmable syringe pump. The software automates all aspects of the flow rate profile, data acquisition, and image analysis. We provide an example of the pelagic diatom Thalassiosira rotula adhered to poly(dimethyl siloxane) surfaces. The described procedure enables the shear rate to be converted to drag force for arbitrary-shaped objects, of utility to the study of many cell species, especially ones that are obviously non-spherical. It was determined that 90% of cells are removed with the application of drag forces less than 3 ⇥ 1012 N, and that this value is relatively independent of the incubation time on the surface. This result is important to understand how marine species interact with polymer surfaces that are used in electrical insulator applications.

keywords: algae, polymer surfaces, insulator fouling, flow cell, video processing, fluid mechanics