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Centralized Architecture of the Electricity Distribution Substation Automation - Benefits and Possibilities

Research output: Collection of articlesDoctoral Thesis

Details

Original languageEnglish
Place of PublicationTampere
PublisherTampere University of Technology
Number of pages134
ISBN (Electronic)978-952-15-3061-6
ISBN (Print)978-952-15-3044-9
StatePublished - 2013
Publication typeG5 Doctoral dissertation (article)

Publication series

NameTampere University of Technology. Publication
PublisherTampere University of Technology
Volume1122
ISSN (Print)1459-2045

Abstract

Smart grid initiatives around the world show how much the control and protection of distribution networks is expected to change within the next few years. As passive networks with unidirectional power flow evolve into active networks with a variety of different active resources, the requirements for distribution substations will also change, requiring the utilities to take action. Utilities do not want to undertake continuous and costly upgrades of the whole protection system, but there is still a clear need for adapting to new requirements. The need to increase the level of automation in the distribution system has been clearly recognized both on the vendor side and on the utility side. Various concept-level proposals have been presented in order to address the conflicting requirements for low life-cycle costs and the rapid uptake of new technology. The most traditional approach has been to increase the functionality of the bay-level protection and control IEDs (Intelligent Electronic Devices). This approach has been sufficient, while CPU capacity has been steadily increasing and the price of new technology has remained at a reasonable level. The issue in this approach has been the extensive costs of upgrades. New features have also required substantial changes in the substation’s entire secondary system, requiring long maintenance breaks. This PhD thesis investigates how station-level data processing can be utilized to help in creating a future-proof architecture for the secondary system of a distribution substation. The needed technology is evaluated, and an overall life-cycle cost analysis is performed showing the cost benefit of a centralized architecture. The thesis shows that the larger the substation, the greater the benefits of a centralized architecture. It also shows how great is the impact of increased reliability. The outage costs of a network exceed all the other life-cycle costs of the secondary system, and illustrates how focusing on substation automation is a cost-efficient way to improve the reliability of the network. The new architecture enables the re-allocation of substation functionality, as both bay-level and station-level data processing is available. This aspect is researched in the thesis, and a clustering method based on fuzzy c-means clustering is proposed for this re-allocation. When the function requires communication, but does not have strict requirements for response times, station-level implementation can be justified. Complex functionality requiring additional CPU performance and anticipated updates in the near future are clear indications of station-level functionality. In addition to re-organizing the existing functionality, the new architecture also enables the utilization of new features which were not feasible previously. A new measurement method is proposed which emphasizes this aspect by increasing the overall sampling frequency of the substation measurements without increasing the sampling frequency of the individual IEDs. The method is based on Time-Interleaved technology, where the sampling of all the IEDs in the substation is synchronized. However, this synchronization is done in such a way that each IED does not take the measurement at exactly the same time stamp. This is achieved by time-shifting the sampling in the IEDs by a fraction of the sample time. Merging these measurements at the station level creates a single sample stream with a high sampling frequency. The usefulness of the architecture and the new measurement method is tested with a transient-based fault location method. In earlier studies, transient-based methods have not been used in bay-level IEDs because of the strict requirements for the sampling frequency. However, using the measurement method presented in this thesis, transient-based algorithms can also be used without increasing the sampling frequency of individual IEDs.

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