Previous projects in conjunction with projects currently running have studied the use of capacitive couplers, Radio Frequency Current Transformers and Rogowski coils. The aim of this project is to assess the suitability of directional couplers for on line monitoring in comparison to established methods. A directional coupler is essentially a screened conducting plate placed on the outer layer of the semi-conducting material of the cable, with outputs from each end of the sensor being fed to a scope. Due to both the capacitive and inductive effects between the two plates one output from a sensor will be greater than the other, hence the direction from which the discharge emanated from can be determined. The advantage directional couplers offer over other methods is this two-channel output per each sensor, so discharge sites can be pin-pointed, however also means that twice as much data is collected and then needs to be analysed.
This project is concerned with the detection, location and pattern identification of partial discharges in high voltage cable systems. The acoustic emission technique, capacitive coupler technique and high frequency current transducer technique have been investigated. Obtained discharge signals were analysed using statistical patterns and operators, Fourier transform and Wavelet analysis. Artificial neural networks were used to identify different PD sources.
This project is concerned with the three-dimensional (3D) space charge distribution measurement in dielectrics. The pressure wave propagation (PWP) method is applied to measure the space charge distribution. Acoustic lens is used to produce intense pressure wave on a small area of the sample so that the detected signal will reflect the charge distribution in Z direction. By moving the acoustic lens on XY plane using a XY stage, the 3D space charge distribution can be measured.
Good substation earthing is essential for a safe and reliable power system. Methods to improve substation grounding with supporting measurements of earth resistance, and computational models to simulate the possible Ground Potential Rise (GPR) due to injected current surges are of particular interest.
The main objective of the initial work is to develop a reliable computational model for the impedance of substation earthing mats and the distribution of the surface potential that occurs when a power frequency fault current is injected into the earthing system. The commercial package CDEGS MALT has been found to be one of the best currently available, and part of the initial effort was to verify its performance. MALT is being tested with experimental results and also Earthing Standards and literatures formulas available. Extensive work have been done to study the effect of �proximity effect� on the surface potentials in and around the earthing system when comparing with the computer software computations.
Also, study of the potential distribution due to the insertion of a local high resistivity barrier have been carried out. The purpose of using local high resistivity is to skew the potential contours, so the earth potential rise immediately beyond the barrier can be reduced. As the power frequency current can penetrate very deep into the ground, the effectiveness of the high resistivity barrier needs to be examined. Effects of barrier geometry under various system conditions was analysed. Both solid barrier and barrier made of plates with various spacings of gaps were tested in the electrolytic tank and modelled in the CDEGS software.
Production and use of HV DC power cables cause formation of space charge within the insulating material and this can become a serious problem. One of the well known non-destrcutive techniques is the Pulsed Electro-acoustic(PEA). The method makes use of the acoustic wave generated by the charges existing in the sample under an applied pulse voltage and this wave is then detected by a piezo-electric transducer. Presently, construction of the improved Pulsed Electro-acoustic(PEA) system is capable of not only measuring space charge but also conduction current simultaneously on thin plaque specimens under a controlled temperature environment. This additional valuable piece of information enhances comprehension about their relationship. They complement each other to give details about charge carrier generation, transportation and accumulation. Such measurements allow insight into the charging processes taking place within the dielectric under study, and make it possible to select materials and interfaces which minimise the risk of breakdown in HV applications.
This project is concerned with the feasibility of using capacitive coupling techniques to detect partial discharge activity in high voltage cables and cable accessories. In particular the need to develop an accurate method of calibration is required if capacitive couplers are to be used for on-line condition monitoring. Post-processing of measurement data will be developed so that the discharge type and its location can be identified.
Recovery Voltage is a phenomenon of polymeric insulators. It is believed to have close relationship with the aging state and moisture content of the insulator. However the interpretation of the measurement is still open to debate, therefore the aim of this project is to study the relationship of measurement with relevant parameters under controlled environment. This will then lead to a model that will be applicable in actual transformer diagnosis.
This project has been established by the Electrical Power Engineering Group at the University of Southampton, and its collaborators the National Grid Company and Pirelli Cables to address some fundamental issues associated with the application of superconducting technology.
Within existing superconducting equipment designs LN2 is used as both the coolant and electrical insulator. Primarily this project is concerned with power transmission and the potential difficulty for all types of superconducting equipment at the ambient/cryogenic boundary. There exists the potential for electrically weaker thermal bubbles of gas nitrogen to form due to thermal influx either from the outside of a termination or through the conductor.
This project will undertake a fundamental study of the bubble dynamics through the life-cycle stages of nucleation/growth/break-off/rise from surface. A purpose built cryostat has been designed and manufactured in-house enabling investigation of bubble dynamics for a range of different samples and conditions including; liquid nitrogen temperature, heat influx regime, pressure (to 20bar), surface materials and geometries.
This study is currently focused on the examination of the influence of electric fields upon the bubbles and LN2; the pre-breakdown, partial discharge and breakdown for the conditions simulated and materials/geometries realistic to the application of superconductivity technology. The project will furnish the University of Southampton and its collaborators with design data that can only be obtained through such extensive experimental validation.