Utility grids consist of large numbers of components as well as many connections that comprise a network supplying electrical energy. Electricity grids in Europe and elsewhere used to be regarded as a public service at almost any cost required and tended to be overdesigned, over-serviced and often deployed only in a national context. By 2000, however, energy came to be recognized as strategic and no longer at any price. Energy represented a significant portion of domestic production costs and therefore had to be controlled in the face of international competition. In addition to reliability, demand for cost-efficiency became a priority. Components and connections in the grid and must meet power supply requirements. Since most grid assets wear due to mechanisms driven by temperature, electromagnetic field, mechanical forces and other ambient conditions, preventive and corrective maintenance actions are necessary, ultimately leading to replacement. Cost, human resources, materials as well as planned outages form both efforts and risks for utilities. Not undertaking these efforts also forms risks. Therefore, maintenance strategies require careful consideration. A presentation by international expert, Prof. Robert Ross, at the 2019 INMR WORLD CONGRESS will discuss alternative maintenance strategies and which conditions favor which approach. The paper leans on statistical techniques, but even if data is lacking for such analysis, the basic principles may still be applicable and used when selecting methods to repair or replace assets.
In Europe, for example, need for cross-border electricity trade evolved as a way to secure energy supply and cost-efficiency. This internationalization was one of the consequences of the drive towards securing energy supply, keeping energy affordable, protecting the environment, reducing climate change and improving electricity grids. Indeed, the European Community policy has been summarized as: sustainable, secure and affordable energy. This policy had far-reaching consequences. Traditional electricity grids were organized as a chain consisting of power plants interconnected to a high voltage transmission network, a distribution network and sale of electric power to end-users also belonged to the utility service. By the end of the twentieth century, this typical utility chain was broken up and electricity production and sales privatized.
Grids are so capital intensive and have such an impact on spatial planning that neither investments nor added right-of-ways are available to build competing parallel infrastructures. As a consequence, there is usually just one electricity grid shared by all providers. As a result, network utilities have kept a monopoly on electricity transmission and distribution. In pursuit of cost efficiency and affordability, however, many countries installed Regulators to supervise and set market prices and quality standards. This assured that the grid owners/operators could not unreasonably drive up prices for their transmission and distribution services. As such, although utilities may have retained a physical monopoly, they were compared to worldwide best practice and faced penalties if underperforming by either poor power quality or excessive expenses. Precise tasks and formulations might differ per country, but the responsibilities of Distribution System Operators (DSOs) and Transmission Operators (TSOs) typically comprise maintaining an electricity network and providing connections between producers and consumers. Moreover, TSOs also have the task of maintaining the balance between supply and demand of electric power. In this context, asset management among utilities aims to provide a resilient, secure and cost-efficient power infrastructure. This leads to solutions that differ from those utilized during most of the twentieth century when technical quality of reliable electrical energy supply faced fewer constraints on financial and workforce resources, as typical for public services. In addition to Corrective Maintenance (CM) and Period Based Maintenance (PBM), new maintenance styles such Condition Based Maintenance (CBM) and Risk Based Maintenance (RBM) were developed. These were supported by tools such as diagnostics, condition monitoring, health index and risk index. CBM focusses on the functionality of grid components while RBM also takes the consequences of dysfunctionality into account, measured in terms of a set of business values that include safety, power quality, security of supply, etc. However CBM and RBM are not always more feasible nor more cost-efficient than conventional styles such as CM and PBM.
Dr. Ross’s presentation at the 2019 INMR WORLD CONGRESS will discuss the background of the transition to modern asset management as well as the Corrective, Period Based, Condition Based and Risk Based maintenance styles along with the circumstances where each is most applicable. Redundancy plays an important role in grids to safeguard security of supply. With the tendency to delay replacement and to harvest as much as possible operational life of assets, this redundancy is also put to its limits. The presentation will pay particular attention to the quality loss of redundancy if the service life of assets is prolonged. An important conclusion is that, even in the absence of failures, an undesirable situation may build up where redundancy is no longer effective. Strategies towards strengthening redundancy will be recommended and a measure for redundancy quality will also be presented.
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