- 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
- Date:
- 2007-2010
- Themes:
- High Voltage Engineering, Modelling and Simulation, Solid dielectrics
- Funding:
- EPSRC, SuperGen V, AMPerES
This project is concerned with establishing whether the occurence of switching/lightning impulses can lead to accelerated ageing of extruded cables. HDPE and XLPE material samples have been manufactured using a mold tool developed as part of this project. The samples then can be electrically aged using one of the high voltage laboratory's impulse generators. A real-time software based monitoring tool has been designed to control the impulse wave-shape and process the measurement data. The obtained results will inform the further development of models describing the multifactor ageing mechanisms that in-service cables experience. The electric field and potential profiles as well as the mechanical deformation of the sample will be observed when using different shaped electrodes.
Primary investigators
- Paul Lewin
- sgs
Secondary investigator
- nld06r
Associated research groups
- Electrical Power Engineering
- Electronics and Electrical Engineering
- Date:
- -2009
- Themes:
- Modelling and Simulation, Condition monitoring, Space and surface charge
The fact that the average service field of most insulating polymers used in high voltage systems is only a fraction (typically ~10%) of their breakdown strength has lead to the belief that the existence of space charges within the insulation may well be the key factor for its long-term electrical degradation. There has been a growing interest nowadays to investigate further the energy dissipation of these mobile and trapped charges and this dissipation process is associated with the emission of visible photons, a process known as electroluminescence (EL). Optical emission has been generally regarded as a direct proof of excited and chemically reactive states within the molecules so the study of the phenomenon could give a better understanding on the processes leading to polymer degradation. The aim for this project is to investigate the factors that influence the occurrence of EL under uniform electric field with the application of 50Hz ac stresses. EL intensity level was observed using a CCD camera and a set of filers were used to examine the spectral characteristics of this light emission. In addition to this, phase-resolved EL measurements were also obtained in order to see how the charge injection processes affect EL behaviour. A dynamic bipolar charge recombination model has been developed in order to allow the simulation of the phenomenon in a plane-plane electrode system.
Primary investigator
Secondary investigator
- ama04r
Associated research group
- Electronics and Computer Science
- Date:
- 2006-
- Theme:
- Industrial Monitoring
Researchers are working on a sensor network that will be capable of monitoring people and machinery in the University's new 55M Pound interdisciplinary cleanroom. The main aims for the system are to increase publicity and awareness (by "opening up" the cleanroom to visitors and staff/students), increase productivity (by allowing users of the cleanroom to see which machines are in use before entering the cleanroom). A primary challenge of the project is the ability of the network to be energy-efficient, while still providing a reasonably up-to-date and accurate impression of its monitored environment.
In addition to increasing publicity and awareness, the project will also provide a WSN showcase and development platform, and also be able to assist in the administration of certain areas of cleanroom management (by monitoring machine and personnel usage).
Primary investigators
- Geoff Merrett
- asw05r
Secondary investigators
- Luca Berti
- Nick Harris
- Neil White
- Bashir Al-Hashimi
Associated research groups
- Electronic Systems and Devices Group
- Electronics and Electrical Engineering
- Date:
- 2005-2010
- Theme:
- Nanoelectronics
Ni has been electro-deposited on n-type Ge wafers of various substrate resistivities. The Ni-Ge Schottky barrier is characterized and found to be of very high quality for highly doped Ge (0.005-0.02 é-cm) with leakage currents order of magnitudes lower than those fabricated by physical vapour deposition techniques eg. evaporation or sputtering. This technique could be used for low leakage Ge based Schottky barrier MOSFETs. On the other hand, the sharp Schottky interface of Ni to highly doped Ge is crucial for spin polarised carrier injection where the currents are explained by Thermionic field emission theories. Therefore, electrodeposition of a Ferromagnetic metal (Ni) on Ge is a viable fabrication technique for spintronic applications. This technique will be used to investigate spin injection into Ge.
Primary investigator
Secondary investigators
- mkh05r
- xl04r
Associated research groups
- Nano Research Group
- Southampton Nanofabrication Centre
- Date:
- 2005-2008
- Themes:
- Nanomaterials and Dielectrics, High Voltage Engineering, Solid dielectrics
- Funding:
- EPSRC
Morphology of polymers has been widely studied in order to enhance their structural properties. In the case of polyolefin, additives are often used to modify the morphology and improve the macroscopic physical properties. In the last decade, the use of nucleating agents has attracted many interests for improved optical and mechanical properties. Dibenzylidene sorbitol (DBS), a physical molecular organogelator, has shown nucleation efficiency on different polymers, like polyethylene (PE). This study investigates the effect of different amount of DBS on the nucleation and crystallisation of PE. A potential application as dielectric is given by the improved space charge distribution in samples containing DBS.
Primary investigator
- asv
Secondary investigator
- gg04r
Associated research group
- Electronics and Computer Science