Knowledge Discovery from On-line Cable Condition Monitoring Systems - Insulation Degradation and Aging Diagnostics

Lead Research Organisation: University of Strathclyde
Department Name: Electronic and Electrical Engineering


This proposal involves collaborative research between academics at Glasgow Caledonian University (GCU) and the University of Strathclyde (UoS). The primary aim of the project is to apply a cross-disciplinary approach to address the problem of acquiring essential information for diagnostics of on-line condition monitoring of cable insulation on the basis of partial discharge (PD) activity. This will be achieved by developing modern data mining techniques to acquire knowledge directly from on-line, data rich, condition monitoring systems. Analysis of on-line information from applied systems will be supported and validated through extensive, dedicated experiments carried out both in the laboratory environment as well as in practical power distribution systems. Failures in the power distribution network are costly to the operators and they are also a serious issue for consumers, who experience power cuts and disruption to their business and social activities during repairs. If techniques for establishing scientifically the condition of cable insulation and its performance are not developed, similar disruption and excessive cost can result from unnecessary replacement of cable assets on the basis of planned maintenance based purely on age. This proposed research programme will build on three areas in which the investigators have internationally recognised expertise: firstly, measuring and discriminating signal characteristics from high power plant, secondly, determining degradation in oil/paper insulation systems and, thirdly, applying software to determine knowledge entrained in raw data. This programme of research will significantly benefit from the knowledge gained from two recently funded EPSRC projects at GCU and UoS (EP/D048133 and GR/86760) as well as recently completed industrially funded projects. In addition to the academic strengths of the proposers, a very substantial industrial contribution is being provided by EDF Energy: a 30,000 direct cash injection and strong in-kind contribution, i.e. cable samples, unlimited access to data from its on-line condition monitoring systems and to fault/condition reports from its replacement programme as well as access to practical expertise of its staff. Further support from Cable manufacturing company Prysmian Cables and Systems Limited (20,000 in kind), Dow Chemical and PD based condition monitoring equipment provider IPEC Ltd (8,000 in-kind) will ensure breadth of validity of the research and broaden the scope of the project by investigating a range of plant types and set-ups and to ensure more general applicability of the research.


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Description This project, carried out in collaboration with a complementary research team at Glasgow Caledonian University, developed our understanding of electrical discharges in the high voltage (HV) cables that are used in electricity distribution networks. Partial discharges (PD) within the insulation (usually at joints and terminations) erode material and are one of the more common causes of cable failure, which can lead to loss of supply and considerable inconvenience during repair. The research carried out involved measurement of the pulses of electrical current emanating from such defects in the early stages of their development. Since they can only be detected by sensors situated at the ends of cables (often hundreds of metres away), understanding how the pulses propagate and become distorted due to the cable material properties is important for implementing effective diagnostic techniques. Advanced high-frequency electromagnetic modelling software was applied to simulate propagation through the cable once the cable materials had been properly characterised. This model implemented the local excitation of a propagating pulse in the cable, and was combined with the propagation equations for long distances (based on measurements of cable samples) and the measured response of sensors (current transformers). By this means, the process has been fully modelled in a way that allows for better interpretation of the remotely measured signals to relate them to the severity of defects in the cable. Sections of defective 11 kV cable removed from service by an industrial partner were subjected to extensive forensic evaluation, and used to validate several forms of defect identification. Time-of-flight and thermal imaging techniques were used to locate the defects, after which computer aided X-ray tomography and scanning electron microscopy were applied to characterise the defect and identify manufacturing errors in the insulation system. Artificial defects created in a section of EPR cable allowed PD signals to be measured, characterised and added to a library for analysis using the newly developed classification algorithm. Two algorithms for knowledge discovery (Rough Set and Kohonen mapping) were evaluated and the Rough Set method was found to be superior in terms of its ability to interrogate and learn from existing databases, analyse PD activity from on-line monitoring systems, with the ability to evolve continuously and produce knowledge rules on the level of degradation. A novel (K-means) method was applied for automating recognition of PD patterns recorded under conditions in which a phase-reference voltage waveform from the HV conductors is not available. The method has proven particularly useful as it is capable of recognising patterns of PD activity in on-line monitoring applications for both single- and three-phase cables and is also effective for rejecting PD-like interference signals. A new, portable cable PD monitoring system was developed and has been applied to in-service cable PD tests at 4 large power stations. An insulation defect localisation algorithm, based on pulse rise time degradation with distance, was also developed from experiments and the on-site measurement campaign. This allows the system developed to provide an indication of the source and origin of PD.
Exploitation Route Better diagnostic interpretation of partial discharge pulse signals measured at the ends of high voltage cables to assess the severity of insulation defects that may be some considerable distance away.
Sectors Energy

Description Joint research with Glasgow Caledonian University 
Organisation Glasgow Caledonian University
Country United Kingdom 
Sector Academic/University 
PI Contribution University of Strathclyde researchers worked on this project with researchers from Glasgow Caledonian University
Start Year 2009
Description Project partnership with EDF Energy Networks ltd 
Organisation EDF Energy
Country United Kingdom 
Sector Private 
PI Contribution EDF Energy Networks ltd worked with the research team and assisted/contributed to the project outcomes
Start Year 2009
Description Project partnership with Prysmian Cables and Systems Limited 
Organisation Prysmian Cables and Systems Limited
Country United Kingdom 
Sector Private 
PI Contribution Prysmian Cables and Systems Limited worked with the research team and assisted/contributed to the project outcomes
Start Year 2009