Space charge accumulation under the effects of temperature gradient on solid dielectric DC cable

It is well known that existence and accumulation of space charge within the insulating material poses threat to the reliability in the operation of dc power cables. When the cables are loaded under high voltage direct current (HVDC), temperature gradient is developed across the insulation material. In this paper, commercial ac XLPE power cables were used under an application voltage of 80 kV dc with different temperature gradients loaded between the insulating material. Space charge distributions were then measured across the insulation of the cable by means of a modified pulsed electroacoustic (PEA) system with a current transformer attached. Therefore, a replica of a power cable under load conditions could be obtained, which allows us to investigate the formation, migration and accumulation of space charges in a power cable both without and with different temperature gradients consideration across the bulk of the insulating material. Discussion will be made thoroughly in order to understand the space charge phenomenon of power cable under its service temperature

Space Charge Accumulation under Effects of Temperature Gradient and Applied Voltage Reversal on Solid Dielectric DC Cable

A well-known fact of the existence and accumulation of space charge within the insulating material poses threat to the reliability in the operation of dc power cables. When power cables are loaded under high voltage direct current (HVDC), temperature gradient is developed across the insulation. Results of space charge evolution in commercial ac XLPE power cables under an application of 80 kV dc supply at different temperature gradients and during external voltage reversal are discussed in this paper. The space charge distributions were measured across the insulation of the cable by means of a modified pulsed electroacoustic (PEA) system with a current transformer attached. Therefore, a replica of a power cable under load conditions could be obtained, which allows us to investigate the formation, migration and accumulation of space charges in a power cable both without and with different temperature gradients consideration across the bulk of the insulating material during voltage reversal. Discussion will be made thoroughly in order to understand the space charge phenomenon of power cable under its service temperature as space charge accumulation during polarity reversal plays an important factor on the electric field distribution within the insulation material

The 3D nature of a real un-dismantled electrical contact interface

AbstractA 3D contact analysis and modeling suite of tools are developed and introduced in this work. The “3D Contact Map” of an electrical contact interface is presented demonstrating the 3D nature of the contact. It gives information on where the electrical contact spots in a 3D surface profile are located. An X-ray Computer Tomography (CT) technique is used to collect the 3D data to a resolution of around 5μm of a real un-dismantled contact interface for analysis. Previous work by Lalechos and Swingler presented “2D Contact Map” on a 2D contact profile from collected 3D data to a resolution of around 8μm. The main advantages of both 3D and 2D mapping techniques focus on the fact that they are non-destructive and there is no need to dismantle the component of interest. This current work focuses on the 3D mapping technique showing its advantages over the 2D mapping technique. For test purposes, a 16A rated AC single pole switch is scanned after two different current loading tests (0A and 16A). A comparison for the total mechanical area of contact, the number of contact spots and the total contact resistance is conducted using both the 2D and 3D mapping techniques to a resolution of around 5μm

Degradation of road tested automotive connectors

The automotive environment is particularly demanding on connector performance, and is characterized by large temperature changes, high humidity and corrosive atmospheres. This paper presents an initial study of connector performance in terms of temperature profiles taken from road vehicles. The temperature profiles are then simulated using empirical relationships to allow prediction of connector performance. Wire harnesses have been investigated to seek evidence of the connector degradation predicted from the temperature data. Initial indications are that the wire harness shows the type of fretting behavior associated with the temperature changes. Evidence of fretting corrosion was found at the contact interface on tin plated terminals from sealed and unsealed connectors

Statistics Anxiety and Self-Efficacy in Psychology Students: A Challenge for Teaching and Learning in STEM

Statistics and research methods are embedded in the university curricula for psychology, STEM, and more widely. Statistical skills are also associated with the development of psychological literacy and graduate attributes. Yet there is concern about students’ mathematical and statistical skills in their transition from school to HE. A major challenge facing the teaching and learning of statistics in HE is the high levels of statistics anxiety and low levels of statistics self-efficacy experienced by students required to learn statistics as part of another course, and the negative impact of these factors on academic performance. The purpose of the current research was to identify the levels of statistics anxiety and statistics self-efficacy in UG and PGT psychology students; identify perceived causes of this; and explore any practical interventions that could be introduced in attempt to alleviate anxiety and increase self-efficacy. Both quantitative and qualitative data were collected, using measures of anxiety and self-efficacy in statistics and psychology, and focus group discussions. The results showed that students reported higher levels of anxiety and lower self-efficacy for statistics when compared with anxiety and self-efficacy in psychology. Analysis of the qualitative data suggested various factors that increased statistics anxiety levels, such as assessment, and this anxiety prevented students from revising for exams and attending lectures. Factors identified as potentially reducing statistics anxiety and the feasibility of possible interventions will be discussed in the context of psychology and more widely

Implementation of a novel online condition monitoring thermal prognostic indicator system

This research aims to develop a reliable and robust online condition monitoring thermal prognostic indicator system which will reduce the risk of failures in a Power System Network. Real-time measurements (weather conditions, temperature of the cable joints or terminations, loading demand) taken close to underground cable will update the prognostic simulation model. Anomalies of the measurements along the cable will be compared with the predicted ones hence indicating a possible degradation activity in the cable. The use of such systems within a power networks will provide a smarter way of prognostic condition monitoring in which you measure less and model more. The use of suggested thermal models will enable the power network operators to maximize asset utilization and minimize constraint costs in the system

Prognostic indication of power cable degradation

The reliability and the health performance of network assets are of a great interest due to power network operators. This project investigates methods of developing a prognostic capability for evaluating the health and long term performance of ageing distribution cable circuits. From the instant of installation and operation, the insulating materials of a cable will begin to age as a result of a combination of mechanical, thermal and electrical factors. Development of simulation models can significantly improve the accuracy of prognostics, allowing the targeting of maintenance and reduction of in service failures [1]. Real-time measurements taken close to underground cables can update the simulation models giving a more accurate prognostic model.Currently the project investigates a thermal prognostic simulation model which will predict the likely temperature impact on a cable at burial depth according to weather conditions and known loading. Anomalies of temperature measurements along the cable compared to predicted temperatures will indicate a possible degradation activity in a cable. An experimental surface trough has been set up where operation of power cables is simulated with a control system which is able to model any cable loading. The surface temperature of the cable is continuously monitored as well as the weather conditions such as solar radiation, soil moisture content, wind speed, humidity, rainfall and air-temperature<br/

Use of Machine Learning for Partial Discharge Discrimination

Partial discharge (PD) measurements are an important tool for assessing the condition of power equipment. Different sources of PD have different effects on the insulation performance of power apparatus. Therefore, discrimination between PD sources is of great interest to both system utilities and equipment manufacturers. This paper investigates the use of a wide bandwidth PD on-line measurement system to facilitate automatic PD source identification. Three artificial PD models were used to simulate typical PD sources which may exist within power systems. Wavelet analysis was applied to pre-process the obtained measurement data. This data was then processed using correlation analysis to cluster the discharges into different groups. A machine learning technique, namely the support vector machine (SVM) was then used to identify between the different PD sources. The SVM is trained to differentiate between the inherent features of each discharge source signal. Laboratory experiments indicate that this approach is applicable for use with field measurement data

Towards Recyclable Insulation Materials for High Voltage Cables

The preferred material for modern extruded high voltage transmission cables is cross-linked polyethylene (XLPE). This material has excellent thermo-mechanical and dielectric properties, however it is not easily recycled at end of use, raising questions as to its long term sustainability [1]. Therefore research work at Southampton has sought to identify suitable recyclable alternatives to XLPE. Such candidate materials need to have low temperature flexibility and high temperature mechanical stability combined with a sufficiently high electrical breakdown strength

Opening the Black Box: Analysing MLP Functionality Using Walsh Functions

The Multilayer Perceptron (MLP) is a neural network architecture that is widely used for regression, classification and time series forecasting. One often cited disadvantage of the MLP, however, is the difficulty associated with human understanding of a particular MLP’s function. This so called black box limitation is due to the fact that the weights of the network reveal little about structure of the function they implement. This paper proposes a method for understanding the structure of the function learned by MLPs that model functions of the class f:{−1,1}^n->R. This includes regression and classification models. A Walsh decomposition of the function implemented by a trained MLP is performed and the coefficients analysed. The advantage of a Walsh decomposition is that it explicitly separates the contribution to the function made by each subset of input neurons. It also allows networks to be compared in terms of their structure and complexity. The method is demonstrated on some small toy functions and on the larger problem of the MNIST handwritten digit classification data set