This project is concerned with a new approach to the condition monitoring and measurement for Partial discharge (PD) especially in terms of its location along high voltage transformer windings. PD may occur in a transformer winding due to aging processes, operational over stressing or defects introduced during manufacture. The presence of PD indicates a serious degradation and ageing mechanism which can be considered as a precursor of transformer failure. The concept developed in this project is based on the fact that the PD which occurred at any point along the winding produces a signal which contains high frequency components with a bandwidth up to 150-200 MHz, that will propagate as a travelling wave towards both ends of the winding eventually reaching a bushing core bar which will allow high frequency components of the PD signal to propagate to its tap point. In the experiment in the lab enviornment, the measurement of PD signals is obtained using Radio Frequency Current Transducers (RFCT) from both ends of the winding which are connected to earth via the bushing tap and neutral earth connection respectively. A new approach is need to be developed for location by using simualtion and digital signal processing techniques. An experiment has been developed that can be used to create common types of PD sources artificially in order to investigate the applicability of the proposed methods.
In order to provide a robust infrastructure for the transmission and distribution of electrical power, understanding and monitoring equipment ageing and failure is of paramount importance. Commonly, failure is associated with degradation of the dielectric material. As a result, a great deal of research and development focuses on understanding ageing of materials and designing methods for condition monitoring. Smart dielectrics are materials which contain a chemical group that produces a measurable response depending on local environmental changes. The introduction of a smart moiety into a chosen material is a potentially attractive means of continual condition monitoring as the system is passive (requiring no maintenance), provides a clear visual output indicative of the local environment, and could be applied to equipment as a coating or even make up part of the bulk dielectric. This project is a collaboration between the Tony Davies High Voltage Laboratory and the research group of Professor Richard C D Brown in the Department of Chemistry at Southampton University. It is important that any introduction of smart groups into the dielectric does not have any detrimental effect on the desirable electrical and mechanical properties of the bulk material. Liquid crystals are currently the subject of investigation as they are widely known to exhibit dramatic changes which are electric field dependant. It is possible to encapsulate droplets of liquid crystal in a host polymer to form a ââ¬Åpolymer dispersed liquid crystalââ¬? (PDLC). Such materials are manufactured into films which can then be used in a variety of applications. It is possible to rigorously control liquid crystal composition and material microstructure in order to produce PDLCs which ââ¬Åswitchââ¬? between clear and opaque states depending on changes in the local electric field, therefore making PDLCs potentially attractive smart dielectrics.
Electric propulsion (EP) can provide an order of magnitude increase in the specific impulse over conventional chemical propulsion giving significant reductions in the mass of propellant needed for a spacecraft. EP thrusters are being increasingly used on modern large telecommunications satellites, primarily for orbit control (NSSK). However, for attitude control chemical thrusters are used, meaning that two separate propellant types are required along with their associated storage tanks, flow control, etc.
There has been recent interest in replacing the chemical propulsion system with electric thrusters for attitude control (AC) thus providing significant systems advantages in terms of mass, complexity and integration. Such a spacecraft has been given the name, ââ¬ËAll-electric Spacecraftââ¬â¢.
One promising candidate for an AC thruster is the hollow cathode thruster (HCT). Hollow cathodes have been developed over the last 50 years or so and are used in gridded ion engines (GIEs) (for the main discharge and neutralizer) and in Hall Effect Thrusters (HETs) as an electron emitter. There is the possibility of using them as stand-alone thrusters (with an anode electrode) and most of the pioneering work on HCTs has been done at the university of Southampton. Nonetheless, the basic mechanism for thrust production has not been determined and the realization of a practical HCT with adequate performance for application to All-electric Spacecraft will need a much better understanding of the device.
To gain this understanding and to design and build a prototype thruster which could meet the necessary performance requirements, the European Space Agency (ESA)/ESTEC has recently funded a Technology Research Programme (TRP) project. Within this project, semi-empirical and analytic models will be developed, a thruster designed and testing to validate the models. Previous performance calculations have almost solely been based on indirect thrust measurements using a target pendulum onto which the thruster plume impacts; this method is not accurate enough and new measurements will be performed at Aerosapzio in Siena using a direct thrust balance. In addition, the effects on the application of a magnetic field to improve performance will be investigated both theoretically and experimentally.
Electric propulsion (EP) can provide an order of magnitude increase in the specific impulse over conventional chemical propulsion giving significant reductions in the mass of propellant needed for a spacecraft. EP thrusters are being increasingly used on modern large telecommunications satellites, primarily for orbit control (NSSK). However, for attitude control chemical thrusters are used, meaning that two separate propellant types are required along with their associated storage tanks, flow control, etc.
There has been recent interest in replacing the chemical propulsion system with electric thrusters for attitude control (AC) thus providing significant systems advantages in terms of mass, complexity and integration. Such a spacecraft has been given the name, ââ¬ËAll-electric Spacecraftââ¬â¢.
One promising candidate for an AC thruster is the hollow cathode thruster (HCT). Hollow cathodes have been developed over the last 50 years or so and are used in gridded ion engines (GIEs) (for the main discharge and neutralizer) and in Hall Effect Thrusters (HETs) as an electron emitter. There is the possibility of using them as stand-alone thrusters (with an anode electrode) and most of the pioneering work on HCTs has been done at the university of Southampton. Nonetheless, the basic mechanism for thrust production has not been determined and the realization of a practical HCT with adequate performance for application to All-electric Spacecraft will need a much better understanding of the device.
To gain this understanding and to design and build a prototype thruster which could meet the necessary performance requirements, the European Space Agency (ESA)/ESTEC has recently funded a Technology Research Programme (TRP) project. Within this project, semi-empirical and analytic models will be developed, a thruster designed and testing to validate the models. Previous performance calculations have almost solely been based on indirect thrust measurements using a target pendulum onto which the thruster plume impacts; this method is not accurate enough and new measurements will be performed at Aerosapzio in Siena using a direct thrust balance. In addition, the effects on the application of a magnetic field to improve performance will be investigated both theoretically and experimentally.
Design of Experiment (DOE) is a technique used to make effective and controlled experimentation and simulations, it helps in reducing the number of simulation runs. This will be very helpful in heterogeneous systems, since simulating such system is costing a lot of CPU resources and computations which leads to prohibitive simulation's time. Energy harvesting system is one of these heterogeneous (multi-physics) systems that contains components from different domains such as electrical both analogue and digital, mechanical, magnetic and thermal; simulating this type of system will result in prohibitive cost unless utilising the power of DOE. In addition to that, DOE enables mathematical modeling to study the behavior of these systems and enable optimising performance of these complex systems efficiently.
Design of Experiment (DOE) is a technique used to make effective and controlled experimentation and simulations, it helps in reducing the number of simulation runs. This will be very helpful in heterogeneous systems, since simulating such system is costing a lot of CPU resources and computations which leads to prohibitive simulation's time. Energy harvesting system is one of these heterogeneous (multi-physics) systems that contains components from different domains such as electrical both analogue and digital, mechanical, magnetic and thermal; simulating this this type of system will result in prohibitive cost unless utilising the power of DOE. In addition to that, DOE enables mathematical modeling to study the behavior of these systems and enable optimising performance of these complex systems efficiently.
Interest is rapidly increasing regarding the application of partial discharge (PD) diagnostics for the task of condition monitoring of HV plant. Put simply, utilities require the tools and fundamental understanding to interpret on-line PD data and relate it to the health of their assets. This project aims to investigate the PD generated by a specific type of three-phase distribution cable: that of paper insulated lead covered construction (PILC). This specific design of cable is of great interest to the utilities that operate Londons' distribution network as it is widely used and is approaching the end of its operational life - significant increases in failure rates have already been identified. An improved understanding of the relationship between PD activity and the various failure mechanisms associated to this cable design is key to accurate analysis in the future.
An experiment has been designed and constructed with the capability of stressing cable sections in a manner similar to circuits in the field. A number of cable samples have been fabricated with defects that are known to reduce the service life of operational circuits. The hope being that the signals generated by these samples under known laboratory conditions, will exhibit similar characteristics to those generated in the field. Therefore, any discrimination or characterisation algorithms that we develop using the experimental data should be readily transferrable to currently operational systems.
Existing induction based harvesting devices power by ambient vibrations are designed around an inertial mass mounted on a spring systems. Such arrangements are linear resonators with very simple structures and strong amplification at their resonant frequency. However they have one major limitation namely their very narrow resonant peak, this translates in very low power generation when the excitation frequency (ambient vibrations) deviates for the resonant frequency of the spring-mass system. Different strategies have been studied to widen the bandwidth of such devices but all of them complicate the simple mass-spring system of such devices. In this project a magnetic circuit is added to the induction devices as it will increase the coupling between the mechanical and electrical domain, however this addition will not complicate the mass-spring system structure of the device. The addition of the of the magnetic circuit will complicate however the design and analysis part, as the linear behaviour of the system is modified and FEM models of the device coupled with a system simulation will be needed to fully characterize the induction harvester. The losses in the magnetic circuit have to be also properly characterised and accounted to fully understand the benefits of the iron core. The possibility to create a bi-stable device in this configuration will be also investigated.
Oil is an important part in power transformers. It serves as both the electrical insulation and coolant and is in contact with metals and the paper insulation. Contaminants such as metal filings or cellulosic residual can be formed in the oil, especially for the transformers with aged paper insulation. These contaminants could form a bridge under the influence of the applied electric field. The bridge may potentially act as a conducting path between two different potentials within the transformer structure, leading to partial discharges or insulation failure. Experimental studies of contaminants motion under both dc and ac voltages will be done in the project. In addition to live optical observation and capturing of bridging phenomena between two electrodes in oil under different voltages, contamination levels and oil and paper insulation conditions, electrical conduction currents and partial discharges will also be measured simultaneously during bridging. These experimental results should allow one to establish a good understanding of contamination and its relation to electrical performance and pre-breakdown phenomena. To aid the understanding of bridging dynamics in the contaminated oil, a numerical model of particle movements and their accumulation at high field regions will be developed. It will be based on the hydrodynamic drift-diffusion approximation for the particles motion under dielectrophoresis force.