Development of Electric Field Stress Control Devices for a 132 kV Insulating Cross-arm using Finite Element Analysis

Insulating cross-arms (ICAs) allow compaction or upgrading of transmission lines. The process of designing and verifying the performance of electric-field grading devices is reported for rigid cross-arms on a 132 kV lattice tower. For the grounded end, traditional grading devices resembling rings which follow the general shape of the insulators were designed. For the high-voltage end, an iterative process yielded a novel grading device which is a unibody piece of cast aluminium that manages the field on all four ICA members. Finite-element analysis simulations show that the electric-field magnitude at the triple junctions of the insulating members meet the design criteria of 3.5 kV/cm. Also, the field magnitude on the metallic end-fittings and electric-field grading devices is maintained below 18 kV/cm. The corona extinction test was performed on ICA assemblies showing that the grading devices can effectively control the electric field at voltages up to 132 kV since the average corona extinction voltage was 173.7 kV, well above the required value. The complete ICA assemblies were installed on an existing line in Scotland in August 2013. This paper provides a set of recommendations for use of FEA in the design of complex insulation geometries

A Trial Installation of High Voltage Composite Cross-arms

Four high voltage composite cross-arms have been installed as part of a non-energised trial taking place in the Scottish Highlands. The non-cylindrical geometry of their two main structural members offers improved mechanical strength-to-weight ratio compared to cylindrically-shaped insulators of similar cross-sectional area. The instrumentation system aims to monitor mechanical performance through the use of embedded strain gauges and a combination of a load cell, accelerometer and inclinometer at the cross-arm nose. An industrial data capture and control platform is used to capture sensor outputs and store them until retrieval. Networked cameras with local storage capabilities are used to capture video recordings of the cross-arms. The trial has helped establish handling, transportation and installation procedures. The first results from the instrumentation system indicate the resilience of the cross-arms to winds reaching up to 151 mph (243 km/h) while no irregularities regarding snow and ice accretion have been observed

A Grading Device

The present invention relates to grading devices (1) for reducing electrical stress in two or more electrically insulating members (29) of an electricity network tower. Preferably, a grading device (1) for reducing electrical stress in two or more electrically insulating members (29) of an electricity network tower, each electrically insulating member (29) having means for connecting the electrically insulating member (29) to an electrical power line supported by the electricity network tower, is provided, wherein: the grading device (1) includes two or more grading rings (3, 5, 7, 9), each of which is shaped so that in use it completely or substantially surrounds a respective one of the electrically insulating members (29); and the two or more grading rings (3, 5, 7, 9) are connected together

‘Warrant’ revisited: Integrating mathematics teachers’ pedagogical and epistemological considerations into Toulmin’s model for argumentation

In this paper, we propose an approach to analysing teacher arguments that takes into account field dependence—namely, in Toulmin’s sense, the dependence of warrants deployed in an argument on the field of activity to which the argument relates. Freeman, to circumvent issues that emerge when we attempt to determine the field(s) that an argument relates to, proposed a classification of warrants (a priori, empirical, institutional and evaluative). Our approach to analysing teacher arguments proposes an adaptation of Freeman’s classification that distinguishes between: epistemological and pedagogical a priori warrants, professional and personal empirical warrants, epistemological and curricular institutional warrants, and evaluative warrants. Our proposition emerged from analyses conducted in the course of a written response and interview study that engages secondary mathematics teachers with classroom scenarios from the mathematical areas of analysis and algebra. The scenarios are hypothetical, grounded on seminal learning and teaching issues, and likely to occur in actual practice. To illustrate our proposed approach to analysing teacher arguments here, we draw on the data we collected through the use of one such scenario, the Tangent Task. We demonstrate how teacher arguments, not analysed for their mathematical accuracy only, can be reconsidered, arguably more productively, in the light of other teacher considerations and priorities: pedagogical, curricular, professional and personal

Competences of Mathematics Teachers in Diagnosing Teaching Situations and Offering Feedback to Students:Specificity, Consistency and Reification of Pedagogical and Mathematical Discourses

In the study we report in this chapter, we investigate the competences of mathematics pre- and in-service teachers in diagnosing situations pertaining to mathematics teaching and in offering feedback to the students at the heart of said situations. To this aim we deploy a research design that involves engaging teachers with situation-specific tasks in which we invite participants to: solve a mathematical problem; examine a (fictional yet research-informed) solution proposed by a student in class and a (fictional yet research-informed) teacher response to the student; and, describe the approach they themselves would adopt in this classroom situation. Participants were 23 mathematics graduates enrolled in a post-graduate mathematics education programme, many already in-service teachers. They responded to a task that involved debating the identification of a tangent line at an inflection point of a cubic function through resorting to the formal definition of tangency or the function graph. Analysis of their written responses to the task revealed a great variation in the participants’ diagnosing and addressing of teaching issues – in this case involving the role of visualisation in mathematical reasoning. We describe this variation in terms of a typology of four interrelated characteristics that emerged from the data analysis: consistency between stated beliefs/knowledge and intended practice, specificity of the response to the given classroom situation, reification of pedagogical discourses, and reification of mathematical discourses. We propose that deploying the theoretical construct of these characteristics in tandem with our situation-specific task design can contribute towards the identification – as well as reflection upon and development – of mathematics teachers’ diagnostic competences in teacher education and professional development programmes

Global economic burden of unmet surgical need for appendicitis

Background: There is a substantial gap in provision of adequate surgical care in many low-and middle-income countries. This study aimed to identify the economic burden of unmet surgical need for the common condition of appendicitis. Methods: Data on the incidence of appendicitis from 170 countries and two different approaches were used to estimate numbers of patients who do not receive surgery: as a fixed proportion of the total unmet surgical need per country (approach 1); and based on country income status (approach 2). Indirect costs with current levels of access and local quality, and those if quality were at the standards of high-income countries, were estimated. A human capital approach was applied, focusing on the economic burden resulting from premature death and absenteeism. Results: Excess mortality was 4185 per 100 000 cases of appendicitis using approach 1 and 3448 per 100 000 using approach 2. The economic burden of continuing current levels of access and local quality was US $92 492 million using approach 1 and$73 141 million using approach 2. The economic burden of not providing surgical care to the standards of high-income countries was $95 004 million using approach 1 and$75 666 million using approach 2. The largest share of these costs resulted from premature death (97.7 per cent) and lack of access (97.0 per cent) in contrast to lack of quality. Conclusion: For a comparatively non-complex emergency condition such as appendicitis, increasing access to care should be prioritized. Although improving quality of care should not be neglected, increasing provision of care at current standards could reduce societal costs substantially