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EDF Energy uses on-line partial-discharge mapping to determine integrity of aging underground cable.
THE DEVELOPMENT OF A ROBUST ON-LINE PARTIAL-DISCHARGE (PD) MONITORING TECHNIQUE HAS PROMPTED EDF ENERGY to perform routine on-line mapping tests on its underground medium-voltage (MV) cable network. EDF Energy is concurrently reviewing its long-term preventive-maintenance strategy, taking advantage of the increased functionality.
OUTLINING THE OBJECTIVES
EDF Energy, one of the largest energy companies in the United Kingdom, provides electricity to London, as well as eastern and southeastern England. EDF Energy's 11-kV and 6.6-kV (MV) underground cable network is 38,000 km (23,620 miles) long, with a total replacement cost estimated at £4 billion (US$7.7 billion). The financial and environmental costs of replacing all the older cables are prohibitive. Therefore, the utility is seeking to establish maintenance and replacement strategies that will avoid premature replacement and reduce unplanned outages.
The fault rate on the MV network is gradually increasing and, in the longer term, likely to accelerate. This trend conflicts with customer pressure and regulatory incentives to improve network performance and reduce operational costs. Hence, EDF Energy aims to develop a comprehensive suite of condition-monitoring tools to provide a reliable assessment of its cable network to optimize the investment of limited financial resources.
The utility's long-term objectives include improving system reliability, identifying high-risk network sections to objectively prioritize cable replacement and refurbishment, and developing systems and tools that would be suitable for other power-system assets as well.
Cables exhibiting a high level of PD have a greater risk of failure than cables with little or no PD activity. For the past 20 years, off-line PD measurement techniques have been used largely in a reactive capacity to detect potential future failures on cables with a history of poor-reliability performance. Offline techniques are time consuming and require network outages, which present an operational risk.
On-line mapping techniques present no such issues, and they provide a continuous monitoring capability. The on-line techniques that are now available have the potential to offer easy, cost-effective solutions and, importantly, to detect the onset of incipient failures on cables with a previously good reliability record.
MAPPING EQUIPMENT AND TECHNIQUES
More than 600 of the 11-kV feeders on the EDF Energy network are now monitored for PD on-line. In most cases,...