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

The capacitive coupler, acoustic emission (AE) sensor and radio frequency current transducer (RFCT) have been used to detect partial discharge (PD) activity within a 132 kV prefabricated cable joint containing a known defect. Although each of the three methods has been applied individually under different situations, a comprehensive investigation and comparison of these three methods has not yet been made. Results obtained were compared to measurements made using the conventional electrical detection method. The quantification of the capacitive coupler measured signal in mV with a discharge apparent quantity in pC has been investigated and an on-line quantification method proposed. The capacitive coupler has good detection sensitivity and PD location can be realised by studying the time of Right between signals from two sensors. The difference in pulse shape, spectrum and time of flight between an internal discharge and external interference has been investigated. The AE approach has the advantage of being free from electrical interference. However, investigation indicated that AE signals were significantly attenuated within the cable joint. RFCTs were used to detect the discharge current flowing through the cable sheath. Where the detection sensitivity was low, a wavelet de-noising method was applied to process the RFCT signals and proved to tie effective in increasing the measurement signal to noise ratio.

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Comparison of on-line partial discharge detection methods for HV cable joints

This Guide lists the various field test methods that are currently available or under development with guidance on HOW to perform each test. The Guide covers shielded, insulated power cable systems rated 5 kV through 500 kV unless these voltages are modified by the specific "point" document.

IEEE Guide for Field Testing and Evaluation of the Insulation of Shielded Power Cable Systems

Over the last several decades, electricity consumption and generation have continually grown. Investment in the Transmission and Distribution (T&D) infrastructure has been minimal and it has become increasingly difficult and expensive to permit and build new power lines. At the same time, a growing increase in the penetration of renewable energy resources is causing an unprecedented level of dynamics on the grid. Consequently, the power grid is congested and under stress. 
To compound the situation, the utilities do not possess detailed information on the status and operating margins on their assets in order to use them optimally. The task of monitoring asset status and optimizing asset utilization for the electric power industry seems particularly challenging, given millions of assets and hundreds of thousands of miles of power lines distributed geographically over millions of square miles. The lack of situational awareness compromises system reliability, and raises the possibility of power outages and even cascading blackouts. 
To address this problem, a conceptual Power Line Sensor Network (PLSN) is proposed in this research. The main objective of this research is to develop a distributed PLSN to provide continuous on-line monitoring of the geographically dispersed power grid by using hundreds of thousands of low-cost, autonomous, smart, and communication-enabled Power Line Sensor (PLS) modules thus to improve the utilization and reliability of the existing power system. 
The proposed PLSN specifically targets the use of passive sensing techniques, focusing on monitoring the real-time dynamic capacity of a specific span of a power line under present weather conditions by using computational intelligence technologies. An ancillary function is to detect the presence of incipient failures along overhead power lines via monitoring and characterizing the electromagnetic fields around overhead conductors. This research integrates detailed modeling of the power lines and the physical manifestations of the parameters being sensed, with pattern recognition technologies. Key issues of this research also include design of a prototype PLS module with integrated sensing, power and communication functions, and validation of the Wireless Sensor Network (WSN) technology integrated to this proposed PLSN.

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Power line sensor networks for enhancing power line reliability and utilization

This paper describes on-line and off-line partial discharge (PD) measuring techniques applicable to transmission cable terminations. The on-line technique can be utilized for both extruded and pipe-type cable terminations. In pipe-type cable terminations, the on-line technique is only applicable to newly installed terminations, as it requires an internal inductive sensor. In the case of extruded cable terminations, on-line testing is made possible by using an external inductive coupler around the ground connection at the base of termination. Off-line PD measurements utilize high-frequency capacitive couplers. The coupler is attached to the overhead line within 4-feet from the termination under test. The off-line testing is applicable to new and existing cable terminations.

N. Ahmed

Papers

Partial discharge measurement in transmission-class cable terminations