- Date:
- 2005-
- Theme:
- Architectures and Interfaces
This research has proposed a hardware/software architecture that provides equal weighting to all node functions; for example, communications, energy management, intelligent sensing, locationing and actuation. This promotes modular design, code reuse, and protocol standardisation in the development of all node functions.
Primary investigators
- Geoff Merrett
- asw05r
Secondary investigators
- ddj07r
- ebm07r
Associated research groups
- Electronic Systems and Devices Group
- Electronics and Electrical Engineering
- Date:
- 2004-
- Theme:
- Simulation, Modelling and Evalution
- Funding:
- EPSRC
Project Aims
Simulation is heavily used in WSN research, but results are only as realistic as the models that they are built around. To ensure a close correlation between simulation and practical results, this research has developed communication, sensing, energy and timing models. WSNsim (a simulator for WSNs) has been developed as a model-centric simulator built around a structured ââ¬Ëunifiedââ¬â¢ stack for communications, energy management and intelligent sensing.
WSNsim: A Simulator for WSNs
WSNsim (Wireless Sensor Network Simulator) was developed to debug, evaluate and improve algorithms developed at the University. WSNsim is an in-house object orientated discrete-event simulator for WSNs, developed using Microsoft Visual Studio .net 2005 (due to limited support and documentation, it is not currently available as open-source).
Left: The Structure of WSNsim, Right: A Network Under Simulation in WSNsim
As shown above, WSNsim gives considerable emphasis to the range of environmental and physical models that it encompasses. Furthermore, the use of a ââ¬Ëunifiedââ¬â¢ stack for communications, energy management and intelligent sensing further increase the attention that WSNsim gives to these areas, while also allowing the simulation of code designed using a structured layered process.
Environmental and Physical Modelling
To support WSNsim, a range of environmental and physical models were investigated, encompassing communication, energy, sensing and timing.
Modelling Wireless Communication and Propagation
The communication model considers both path loss (using an empirical path loss model) and packet reception (by considering BERs at a per-byte level). Energy models are proposed for energy stores (batteries and supercapacitors), energy sources (photovoltaics and vibration energy harvesters), and energy consumers (radio transceivers, microcontrollers, and peripherals).
Modelling Energy Stores (Top Left), Energy Sources (Top Right) and Sensors (Bottom)
Sensor models account for errors and inaccuracies in sensed data by modelling the sensor hardware. Timing models consider the differences between the ââ¬Ëtrueââ¬â¢ time, and the nodesââ¬â¢ perceptions of time.
Primary investigator
Secondary investigators
Associated research groups
- Electronic Systems and Devices Group
- Electronics and Electrical Engineering
- Date:
- 2004-
- Theme:
- Algorithms for Wireless Sensor Networks
The development of wireless sensor networks presents extensive research challenges in retaining a "reasonable" network lifetime under constraints imposed by the limited energy reserves inherent in small, locally powered embedded nodes. This research addresses these challenges through the development and validation of IDEALS/RMR - an application independent, localised system to control and manage the degradation of a network through the novel combination of information management (assessed through RMR) and energy management (controlled by IDEALS) - a union which increases the network lifetime at the expense of discarding often trivial data. To evaluate these algorithms, a simulator (WSNsim), was developed to enable high level network and performance analysis. Results show that IDEALS/RMR can provide controlled network degradation under load conditions.
Primary investigator
Secondary investigators
Associated research groups
- Electronic Systems and Devices Group
- Electronics and Electrical Engineering
Dielectric breakdown phenomena pose major scientific and technological problems. The degradation of polymer insulation under high electric stress is associated with space charge formation. In fact, space charge accumulation in dc regime is the main reason that prevents the use of polymers as insulation for high voltage direct current cables. Whilst the Laplacian field, may be adequate representation of that which is experienced by an insulator over a short time, it is well appreciated that, over longer time scales, this becomes modified through the injection of charge carriers from the electrodes or the dissociation of neutral species within the bulk. These charged species subsequently migrate through the dielectric before becoming trapped at specific sites within the material. The net result of these processes is that the local field at particular sites within the insulation may be substantially different from that which would be experienced in the absence of such phenomena. In particular, the local field may greatly exceed that the threshold stress above which the degradation takes place, so causing accelerated electrical ageing of the material and eventual failure. Whilst this may occur through the action of both ac and dc fields, space charge is intrinsically more problematical under dc conditions. The development of polymer-insulated dc cables therefore represents a particularly challenging technological problem. Consequently, recently research into space charge formation and its effect on the ageing and failure mechanisms of insulating materials has intensified, not only because of its engineering importance, but also through technical advances made in instrumentation.
Attempts have been made to investigate the electric field distribution in polymeric power cables under dc conditions. Previous attempts were less significant as little knowledge on space charge distribution in the cable. Cable space charge measurement system has been set up in the High Voltage Lab and electric field in the presence of space charge has been estimated using empirical formula. This unique cable space charge measurement system enables us to investigate space charge distribution as a function of electric field, temperature and even polarity reversal, an operation often used in dc power transmission. However, for a practical dc power cable the electric field is affected by conductivity of the material which is a function of both temperature and electric field. The coupled problems impose significant difficulty to know electric field distribution in high voltage dc power cables therefore a serious thread to the reliable operation of dc power cables.
The project concerns the accurate determination of electric field distribution in the presence of space charge where electrical conductivity of the material will be determined as a function of both electric field and temperature. The coupled equations will be solved using a numerical software package. An algorithm will be produced so that the future experimental data can be loaded and electric field distribution is ready to be displayed.
Primary investigator
Secondary investigator
- ctc05r
Associated research groups
- Electrical Power Engineering
- Electronics and Electrical Engineering
- Date:
- 2006-2010
- Themes:
- Modelling and Simulation, Space and surface charge, Environmental modelling
To date, there have been a number of attempts in simulating surface discharge. These works generally fall into one of the two categories: stochastic or deterministic. Stochastic techniques are able to produce discharge figures that have fractal characteristics but do not take into consideration any of the physical processes involved in the discharge phenomenon. Deterministic approaches, on the other hand, take ionisation, attachment, recombination, photo-ionisation and photo-emission processes into account. This project, therefore, pursues a deterministic scheme which is characterised by a set of partial differential continuity equations coupled with the Poissonââ¬â¢s equation. These equations govern the evolution of charged particles along the surface streamer channel. Due to the non-linearity and sharp gradient nature of the problem at hand, an accurate numerical method is required. Various numerical techniques have been compared including the Eulerian differencing, Lax-Wendroff and the Flux-Corrected-Transport (FCT) algorithm. The FCT method has shown superiority owning to its accuracy, stability and nonââ¬ânegativity. The principle of the method is based on the flux limitation process which makes the best out of the low and high order schemes without introducing either diffusion or spurious oscillation. Possionââ¬â¢s equation, on the other hand, can be solved using the disc method or 3-D finite-difference method depending on the accuracy desired. From simulated results, one can obtain the streamer velocity, charged particle densities and electric field along the streamer channel. In addition, the discharge figure can be achieved by considering the growth of the future streamer in the direction of the maximum field induced from the preââ¬âexisting streamers. By using a different set of swarm parameters, it is also possible to simulate surface discharge in SF6 gas.
Primary investigators
Secondary investigator
- ntt05r
Associated research groups
- Electrical Power Engineering
- Electronics and Electrical Engineering
- Date:
- 2006-2009
- Themes:
- High Voltage Engineering, Space and surface charge
- Funding:
- National Grid plc
The aim of the project is to develop an experiment to measure surface discharge using the Pockels technique. As surface discharge is an inevitable phenomenon leading to failure of the insulation systems in most practical gas-insulated-switchgear (GIS) and high voltage transformers, it is desired to measure surface charge density and distribution. On the other hand, results obtained from measuring surface discharge helps gain insight into the mechanism of streamer formation along the interface of gas and solid insulators. Other measurement techniques in the field include the Lichtenberg figures, dust figures and capacitive probes. However, all of these methods suffer from a number of shortcomings which do not allow charge quantification and capturing of discharge dynamics at the same time as the Pockels technique offers. The principle of the electro-optic system is based on the Pockels effect of some materials such as Bi12SiO20, Bi12GeO20, and LiNbO3, which under an electric stress have the characteristic of retarding the phase of the linearly polarised input light. Other components of the rig include a laser source, beam expander, beam splitter, optical phase modulator (OPM), vacuum chamber, lens, pinhole, CCD camera and synchronisation control circuit. Discharge images are recorded at 1 ms interval during the application of the external voltage and transferred afterwards to a personal computer for further image processing. Results obtained from two cycles of AC voltage in dry air have revealed a number of discharge characteristics namely the polarity effects, back-discharge, residual charge effects etc. In addition, measurements at various pressures have been performed in order to investigate the effects of pressure on the discharge patterns. The influences of electropositive and electronegative gases have also been studied. Other aspects of surface discharge which require further investigations include improving the framing rate, measuring discharge along the solid/liquid interface and studying the electrode shape impacts.
Primary investigators
Secondary investigator
- ntt05r
Associated research groups
- Electrical Power Engineering
- Electronics and Electrical Engineering
- Date:
- 2004-2012
- Themes:
- High Voltage Engineering, Condition monitoring, Solid dielectrics, Liquid dielectrics
- Funding:
- National Grid plc
Transmission and distribution operators throughout the world control significant populations of ageing large transformers which use mineral oil and paper as the dielectric insulation. Some of these transformers are reaching the end of the projected service life and subject to various end-of-life failures which cause the transformer to be taken out of service.
One failure mode, for which no root cause has been identified, occurs in the inter-phase barrier region. This is the mechanical space between the high voltage series coils in the transformer. This failure mode leaves evidence of surface tracking along the inter-phase barrier boards.
This project is supported by UK National Grid and has the principle goal of understanding this failure mode with a secondary goal of early life failure prevention. The project has twin themes of high voltage engineering and dielectric ageing.
This is an experimentally based project and has resulted in a unique experimental apparatus to be developed. The apparatus permits high voltages from two separate voltage sources to be applied to a scale model of inter-phase barrier boards under controlled conditions of moisture and temperature. The voltage sources can be controlled independently of each other in terms of amplitude and phase.
The development of the apparatus, along with some novel side experiments is revealing some interesting properties of surface tracking on pressboard insulation. The results from this study should help transmission and distribution operators in long term asset management.
Primary investigators
Secondary investigator
- pmm2
Associated research group
- Electronics and Computer Science
- Date:
- 2004-2009
- Themes:
- High Voltage Engineering, Condition monitoring
- Funding:
- AMPerES, SuperGen V, EPSRC
Partial discharge (PD) may have a significant effect on the insulation performance of power apparatus. Insulation performance and properties can be influenced by PD activity from different types of PD sources. Therefore, PD source identification and diagnosis is of interest to both power equipment manufacturers and utilities.
The main aim of this research is to investigate approaches that may be used to facilitate on-line condition monitoring of high voltage assets. The application of machine based learning techniques to partial discharge (PD) discrimination will be researched. The use of support vector machines (SVM) has been assessed as a potential tool for PD source identification. A comprehensive automatic PD identification system has been developed and assessed. The approach has also been applied to PD monitoring of power transformers using an electro-optic modulator based PD data transmission system.
Current work is concentrating on methods of identifying PD signal buried in measurement noise and methods of discriminating between PD signals from multiple discharge sites within an item of power plant.
Primary investigator
Secondary investigator
- lh3
Associated research group
- Electronics and Computer Science
- Date:
- 2007-2010
- Themes:
- High Voltage Engineering, Solid dielectrics
- Funding:
- EPSRC, SuperGen, AMPerES
Electrical generation and distribution equipment employs both liquid and solid materials in its construction. Unfortunately, when such equipment was brought into service many decades ago, little thought was paid to its environmental impact. SuperGen is a major government and industry funded project which tackles the issue of how we can generate and distribute electrical power in a responsible, sustainable and environmentally friendly manner. For our part at Southampton, we are looking at new materials to replace those currently used in such plant, which are less detrimental to the environment both in service and at the point of disposal. The project has two facets, dealing with liquids and solids.
The first part of the project deals with liquid insulation systems. Liquids are used both as an insulator and a coolant in many items of high voltage plant including cables, transformers and switchgear. However, the current oil employed in almost all of these applications is mineral oil which is toxic to the environment and comes from a non-renewable source (crude oil). To date, a biodegradable synthetic oil (dodecylbenzene) and a range of vegetable oils have been investigated as to thier suitability to replace mineral oil in existing and new plant. They have been thermally aged under different atmospheres (ranging from air to nitrogen) to simulate equipment conditions, and their ageing behaviour has been characterised by a variety of optical and electrical techniques. The various available oils have been sucessfully ranked in terms of thier ability to withstand ageing and suitable biodegradable oils for use in existing plant have been recommended. Current work concerns optimising and improving, through the use of additives and blending, thier ageing resistance.
The second part of the project deals with solid insulation systems. Currently, the majority of solid (extruded) power cables employ cross-linked polyethylene (XLPE) which has excellent thermal, mechanical and electrical properties but is not easily recycled and hence its use poses serious disposal problems. To replace XLPE, both ethylene and propylene based alternatives have been proposed which have the advantage of being recyclable after use. So far, the thermal, mechanical and electrical properties of a range of different systems have been investigated and compared to XLPE in order to assess thier suitability for future cable systems. Current work is focused on optimising the mechanical, thermal and electrical properties through suitable choice of material and processing conditions.
Primary investigators
- asv
- sgs
Secondary investigator
Associated research groups
- Electrical Power Engineering
- Electronics and Electrical Engineering
- Date:
- 2007-2008
- Themes:
- Nanomaterials and Dielectrics, Solid dielectrics
- Funding:
- EPSRC
This research investigates how polar molecules can affect the behaviour of non polar polymer solids. In the recent years, there has been growing interest in nanocomposites based on a polymer matrix. However, the introduction of polar nanoparticles may involve a penalty in terms of dielectric material properties. By designing a polyethylene matrix with polar molecules we are able to control a series of factors like: microstructures, nucleation density and phase behaviour. Studies have shown the influence of morphology on the dielectric proprieties of polymers.
This project involves a study of polyethylene with different types of polar molecules. We are investigating the effect of small and macro polar molecules. A further investigation looks at the effect of nanoclay dispersed in ethylene vinyl acetate and subsequently nanocomposites based on PE/EVA and nanoclay.
Primary investigator
- asv
Secondary investigator
- gg04r
Associated research group
- Electronics and Electrical Engineering