A Framework for the Prioritization of Underground Transmission Cable Asset Renewal Projects in Power Electric Utility Companies
High voltage transmission lines are one of the most important assets in electricity transmission utility companies. In crowded urban areas, underground power transmission cables, in particular, forms an important part of the electricity grid network. A large number of underground power transmission lines in North America have now been in service for more than fifty years and are already approaching their expected end of life. As a result of the aging network, a large number of underground transmission circuits in many city areas need to be upgraded or replaced through "asset renewal" projects. However, based on the author's experience working in a transmission utility company, the prioritization of underground transmission cable renewal projects is quite challenging as it is not a straightforward process. Some current issues typically encountered by an Asset Manager in a utility company include the following:
- The physical conditions of the underground cable assets are difficult to ascertain in many cases because of their hard to reach or inaccessible installation locations.
- Many tests currently available to determine the remaining life of an underground cable circuit require an actual cable sample to be obtained from the field and tested in a laboratory. Typically, samples of an existing underground cable circuit are hard to obtain and are usually available only after a cable fault has occurred.
- Most high voltage underground cables in North America were installed in the 1950's and 1960's. Due to the age of the system, a majority of the existing circuits will soon require significant refurbishment work or their outright replacement, all within the next five to ten years. It is not feasible to prioritize underground transmission line renewal projects based simply on the age of the circuits because a large number of old underground circuits that are of similar age.
- The asset manager in a transmission utility company, due to limited resources, can typically only make large investments in transmission line asset renewal projects on a limited number of circuits at a given time.
- Underground transmission lines are typically constructed over long geographical distances and are usually installed in public corridors which require the coordination and approval from multiple utility companies, environmental and government agencies. Due to the large number of stakeholders involved and the sometimes complex nature of underground transmission line renewal projects, it can take many years to complete an asset renewal project from the initial planning stage to the final commissioning. In other words, due to the long length of time it takes to replace an underground transmission line circuit, the asset manager in a utility should theoretically initiate asset renewal projects well in advance of when the cable has reached its end of life.
Given that utility companies have only finite resources available, one of the most important goals of asset management in power transmission utilities therefore is to be able to prioritize asset renewal investment projects.
This research reviews the current asset management methodologies in power electric utility companies and identifies the present challenges and problems encountered by utility companies with the current methodologies in managing and prioritizing underground transmission cable asset renewal projects. A more systematic framework for evaluating and ranking underground transmission cable asset renewal investment projects is proposed in the research based on the modeling of uncertainties and on determining the relative importance of a particular transmission line circuit in the power system as it affects the bulk power system reliability.