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/

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

Condition monitoring and prognostic indicators for network reliability

Large-scale investment in transmission and distribution networks are planned over the next 10-15 years to meet future demand and changes in power generation. However, it is important that existing assets continue to operate reliably and their health maintained. A research project is considering the increased use of simulation models that could provide accurate prognostics, targeting maintenance and reduce in service failures. Such models could be further refined with parameters obtained from on-line measurements at the asset. It is also important to consider the future development of the research agenda for condition monitoring of power networks and with colleagues from National Grid, PPA Energy and the Universities of Manchester and Strathclyde, the research team are preparing a Position Paper on this subject

Preliminary investigation on the feasibility of radiometric techniques to detect faults in buried cable joints

This paper investigates the preliminary use of radiometric techniques to the detection of PDs in buried cables, and in particular to cable joints. The transfer function from the source to the detector is a function of the propagation characteristics of the media involved. In the case of radiometric detection the inclusion of soil, in general a lossy and dispersive medium with frequency and content dependent characteristics, further contributes to signal attenuation. The work undertaken here examines whether a repetitive pulse of varying amplitude and frequency, injected into an experimental arrangement that simulates buried power cables, is being detected by two simple antennae above ground. Successful detection of the pulses showed the preliminary possibility of the use of such techniques in PD detection, which creates the need for further experiments and antenna designs to be explored

The development of prognostic tools for MV cable circuits

Cable failures are disruptive, costly to repair and have a serious impact on customer confidence. Thus developing a reliable on-line prognostic tool is of a great interest. An experimental setup has been created to develop a new prognostic thermal model for MV underground cables. This paper introduces a thermal prognostic simulation model based on Support Vector Regression Algorithm which predicts the likely temperature along the cable thirty minutes into the future and is able to detect temperature anomalies which can indicate upcoming failures

The effects of surface hydroxyl groups in polyethylene-silica nanocomposites

Logically, the surface chemistry of filler particles must be a key factor that governs how they interact with a polymer matrix, determining for example, how strongly the particles are bound into the matrix and how easy or difficult it is to achieve a homogenous dispersion of filler particles. This second point is surely one of the most basic challenges when producing a nanocomposite (poor dispersion is frequently stated as the cause of undesirable results). Many attempts have been made to modify the surface chemistry of filler particles through surface functionalization. Typically, this is achieved by chemically attaching polymer chains to the surface of the filler particles. In this paper we try a more direct approach; the surface chemistry of silica nanoparticles is modified by processing them at high temperature. This procedure removes hydroxyl groups from the surface of the filler particles, leaving siloxane groups which are stable at room temperature. Polyethylene composites were produced using both “as delivered” and high temperature processed nanosilica. After heat treatment the particles become hydrophobic which reduces the propensity for water uptake in the resulting nanocomposite and significantly modifies the dielectric response of the material

Numerical thermo-mechanical stress analysis for HVDC cables

Calculating the current rating of paper insulated HVDC cables under low ambient temperatures can require additional mechanical considerations. Under rapid cable heating or cooling processes, an extremely high mechanical stress or a rapid pressure drop can develop due to the strong impregnant thermal expansion or contraction respectively. This may cause plastic deformation of the sheath or the creation of voids. This paper demonstrates the importance of this thermo-mechanical constraint through the application of finite element modelling techniques which permit a coupling of the thermal and mechanical properties within the cable. The results show that the FEA technique can be fully applied to analyze the internal thermo-mechanical stress distribution of the cable and calculate the resulting mechanical stress-limited rating, which provides an alternative to an analytical method previously developed by the same author

Continuous online monitoring of partial discharges in high voltage cables

This paper reviews data acquisition, transmission and processing methodologies for continuous online monitoring of partial discharges in power cable systems. A PD continuous online monitoring system for underground cable circuits using capacitive couplers, LiNbO3 electro-optic modulators, laser, optical switch and optical fibers has been proposed. Data processing methods include pulse shape and spectrum analysis, time of flight analysis, phase-resolved two-dimensional histograms, three-dimensional (phi)-q-n patterns, trend analysis, wavelet-based denoising, alarm strategy and telecommunication function to enable remote control and data download

Experimental studies on surface discharge dynamics and decay under different voltage waveforms and electrode shapes

This paper studies the development and decay of surface discharge under various voltage waveforms and electrode shapes in air at atmospheric pressure. The electro-optical Pockels method is utilised to measure and quantify the distribution of surface charge. Charge is deposited on the surface of the Bismuth Silicon Oxide (BSO) sensing crystal from a high voltage needle or mushroom electrode. Sinusoidal, square pulse and ramp voltage waveforms of different polarities are generated in order to investigate the differences in the total surface charge, inception voltage and distribution pattern of positive and negative discharges. The total charge deposited can be found by integrating the post-processed charge density over the entire surface. This technique also enables the study of charge decay with time