Power Line Sensor Networks for Enhancing Power Line Reliability and Utilization

The task of monitoring asset status and optimizing asset utilization for the T&D industry, given millions of assets and hundreds of thousands of miles of power lines distributed geographically over millions of square miles, seems particularly challenging if not impossible. Given the traditionally high cost of sensing and communications, the grid has minimal 'smarts' with much of the intelligence located at major substations. Dramatic reductions in sensor, computing and communications costs, coupled with significant performance enhancements has raised the possibility of realizing widely and massively distributed sensor networks (SNs) to monitor utility asset status. Under NEETRAC funding, a survey was conducted to review existing sensor technologies and products, and to estimate the possibility of extending these to realize distributed SNs. Possible applications for such SNs were also explored, as was the issue of cost point at which such networks would become commercially viable. This paper provides an overview of the highlights from the detailed survey that was conducted, and identifies 'gaps' in currently available sensor technologies, both from a performance and cost point.

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A Survey on Technologies for Implementing Sensor Networks for Power Delivery Systems

This paper presents an overview of the state of the art on the research on Dynamic Line Rating forecasting. It is directed at researchers and decision-makers in the renewable energy and smart grids domain, and in particular at members of both the power system and meteorological community. Its aim is to explain the details of one aspect of the complex interconnection between the environment and power systems. The ampacity of a conductor is defined as the maximum constant current which will meet the design, security and safety criteria of a particular line on which the conductor is used. Dynamic Line Rating (DLR) is a technology used to dynamically increase the ampacity of electric overhead transmission lines. It is based on the observation that the ampacity of an overhead line is determined by its ability to dissipate into the environment the heat produced by Joule effect. This in turn is dependent on environmental conditions such as the value of ambient temperature, solar radiation, and wind speed and direction. Currently, conservative static seasonal estimations of meteorological values are used to determine ampacity. In a DLR framework, the ampacity is estimated in real time or quasi-real time using sensors on the line that measure conductor temperature, tension, sag or environmental parameters such as wind speed and air temperature. Because of the conservative assumptions used to calculate static seasonal ampacity limits and the variability of weather parameters, DLRs are considerably higher than static seasonal ratings. The latent transmission capacity made available by DLRs means the operation time of equipment can be extended, especially in the current power system scenario, where power injections from Intermittent Renewable Sources (IRS) put stress on the existing infrastructure. DLR can represent a solution for accommodating higher renewable production whilst minimizing or postponing network reinforcements. On the other hand, the variability of DLR with respect to static seasonal ratings makes it particularly difficult to exploit, which explains the slow take-up rate of this technology. In order to facilitate the integration of DLR into power system operations, research has been launched into DLR forecasting, following a similar avenue to IRS production forecasting, i.e. based on a mix of statistical methods and meteorological forecasts. The development of reliable DLR forecasts will no doubt be seen as a necessary step for integrating DLR into power system management and reaping the expected benefits.

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Forecasting for dynamic line rating

Electrical load growth and the addition of renewable energy generation occur at a rate that can outpace transmission development. As a consequence, transmission lines may become constrained. To accommodate load growth or distributed generation connections, one option is to operate existing transmission facilities up to their actual physical capacity rather than a conservative estimate of line capacity. Dynamic thermal rating of transmission lines provides actual current-carrying capacity of overhead lines based on real-time operating conditions. Dynamic Thermal Line Rating (DTLR) approaches vary significantly from one study to another in implementation, objectives and outcomes. Existing literature has presented several methodologies for DTLR adoption. This paper provides a comprehensive study of the literature on DTLR. It presents a survey and evaluation of various DTLR technologies, DTLR equipment, challenges with DTLR deployment, real world applications, and future approaches to DTLR implementation. The presented work is organized to allow a reader to understand and compare various DTLR approaches.

Dynamic thermal rating of transmission lines: A review

When a wind power system is connected to a network point there is a limit of power generation based on the characteristics of the network and the loads connected to it. Traditionally, transmission line limits are estimated conservatively assuming unfavourable weather conditions (high ambient temperature, full sun and low wind speed). However, the transmission capacity of an overhead line increases when wind speed is high, due to the cooling caused by wind in the distribution lines. Dynamic line rating (DLR) systems allow monitoring real weather conditions and calculating the real capacity of lines. Thus, when planning wind power integration, if dynamic line limits are considered instead of the conservative and static limits, estimated capacity increases. This article reviews all technologies developed for real-time monitoring during the last 30 years, as well as some case studies around the world, and brings out the benefits and technical limitations of employing dynamic line rating on overhead lines. Further, the use of these DLR systems in wind integration is reviewed.

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Review of dynamic line rating systems for wind power integration

This paper describes a method to directly measure the physical sag of overhead electric power transmission conductors. The method used relies on the Global Positioning System (GPS) used in the differential mode. The direct measurement of sag is a main advantage of the concept. The digital signal processing required is described in detail in a four-level configuration. The typical accuracy, response time, problems, strengths and weaknesses of the method are also described.

C. Mensah-Bonsu

Papers

Application of the Global Positioning System to the Measurement of Overhead Power Transmnission Conductor Sag