Konstantinos Kopsidas

A Performance Analysis of Reconductoring an Overhead Line Structure

A holistic computational methodology is employed in this paper to present an analysis of the widely used aluminum alloy conductors (AAAC) performance on a 33-kV wood pole structure. This analysis highlights the basic system properties that influence its mechanical and electrical performance. A comprehensive comparison of the performance of the common AAAC and aluminum conductor steel reinforced (ACSR) conductors erected on the structure is presented, including the study of the increase in operating temperature on the losses, ampacity and sag, in order to identify the most appropriate conductor for the pre-specified structure. Some recently developed high temperature low sag (HTLS) composite conductors are also studied in terms of power transfer uprating on distribution overhead lines. Their performance is examined at normal temperatures instead of the high operating temperatures for which they are specifically designed for, in order to evaluate the benefits they may offer at distribution level voltages.

Induced Voltages on Long Aerial and Buried Pipelines Due to Transmission Line Transients

In a previous paper , the voltage induced onto a 1-km above-ground pipeline by transmission line transients was shown to be significant in comparison to the induced voltage resulting from power system currents. This paper enhances the previous work in three distinct areas. First, both aerial and buried pipelines are considered. Above-ground pipelines are shown to be more at risk from transient-induced voltages. Second, parallelisms of up to 10 km are simulated. The results show that increasing parallelisms do not result in higher induced voltages once a critical distance has been reached. Third, a backflashover from a tower in the vicinity to a pipeline is modeled. This allows conductive coupling to take place at the same time as inductive and capacitive coupling. Backflashovers are shown to be an important consideration in determining the maximum voltages observed on a nearby pipeline.

Optimal Demand Response Scheduling With Real-Time Thermal Ratings of Overhead Lines for Improved Network Reliability

This paper proposes a probabilistic framework for optimal demand response scheduling in the day-ahead planning of transmission networks. Optimal load reduction plans are determined from network security requirements, physical characteristics of various customer types, and by recognizing two types of reductions, voluntary and involuntary. Ranking of both load reduction categories is based on their values and expected outage durations, while sizing takes into account the inherent probabilistic components. The optimal schedule of load recovery is then found by optimizing the customers’ position in the joint energy and reserve market, while considering several operational and demand response constraints. The developed methodology is incorporated in the sequential Monte Carlo simulation procedure and tested on several IEEE networks. Here, the overhead lines are modeled with the aid of either static-seasonal or real-time thermal ratings. Wind generating units are also connected to the network in order to model wind uncertainty. The results show that the proposed demand response scheduling improves both reliability and economic indices, particularly when emergency energy prices drive the load recovery.

A Holistic Method for Conductor Ampacity and Sag Computation on an OHL Structure

The rating current (ampacity) of a conductor erected on a particular overhead line (OHL) structure installed at a specified location is influenced by the conductor, the OHL structure, as well as weather and operational parameters. Many studies have been carried out regarding calculating an aerial bare conductors ampacity at a steady-state conductor temperature, but without considering the OHL structure as part of the system. In this paper, a holistic methodology for calculating the conductors ampacity and sag at any temperature and power frequency, erected onto a prespecified OHL structure is developed, considering together the mechanical and electrical parameters of the overall system. This methodology incorporates the conductors basic material properties allowing the calculations to be applied to newly developed high-temperature low-sag composite conductors. In this way, it becomes possible to identify, at the system level, the potential benefits that may result from the improved performance of these conductors as well as to indicate new sizes that may better fit a prespecified system, optimizing its performance. The methodology is also validated with a real system application, resulting in correct predictions of the performance of a four-span double-line system.

Comparison of Transient and Power Frequency-Induced Voltages on a Pipeline Parallel to an Overhead Transmission Line

An analysis of the voltages induced on a 1-km pipeline by a parallel overhead transmission line has been carried out when the transmission line is carrying power frequency (50 Hz) current and when it is subject to the propagation of a lightning or switching transient. A frequency-based circuit modeling technique coupled with forward and inverse Fourier transforms is used to carry out this analysis. The relative severity of the induced voltages from power frequency current or transient (lightning/switching) overvoltages is illustrated using the simulation results. The results demonstrate the high relative magnitude of induced pipeline voltages that result from the propagation of lightning transients down overhead lines. The need to model the full overhead line for such an analysis is investigated as is the variation of the level of transmission line/pipeline coupling as a function of the local soil resistivity. Analysis of the level of induced voltage as a function of length of parallelism is also carried out.

Power transfer capacity improvements of existing overhead line systems

The increased demand for power transfer in combination with environmental and economic issues which set constraints to building new lines, force the implementation of new technologies into the existing system in order to improve its power capability. Such methods involve re-tensioning, re-conductoring, or modifying the tower design to utilize composite cross-arms. It is hypothesized that a composite cross-arm and a novel conductor together provide an insulating significant opportunity to increase the overhead line voltage. The paper explores the range of options that could be implemented on an L3 overhead line tower typically used at 275kV in the United Kingdom, and demonstrates clear improvement in power capacitiy through the implementation of new technologies.

Power Network Reliability Evaluation Framework Considering OHL Electro-Thermal Design

Utilities continually investigate ways to optimize the utilization of their existing plant and improve their networks flexibility and resiliency to future uncertainties. With respect to overhead lines (OHL), smart grid solutions aim to increase adequacy through the implementation of probabilistic thermal rating (PTR), dynamic thermal rating (DTR) or novel high temperature low sag (HTLS) conductor technologies. At present, the risks related to these particular solutions, both for the OHL plant and the power network, are not quantified. This paper presents a novel methodology for power network reliability evaluation which integrates a network level sequential Monte Carlo algorithm with a detailed modeling of OHL. This integration facilitates a holistic evaluation of power network reliability as it considers the properties of OHL design technologies and their associated ageing risks. As a result, the network performance (adequacy) and plant risks (ageing) introduced by increased OHL capacities through PTR, DTR, and HTLS solutions can be objectively quantified. An application of the methodology is demonstrated using the IEEE-RTS 96 network which is assessed considering PTR-based OHL capacities.

Assessing the value of employing dynamic thermal rating on system-wide performance

The power grid is under pressure to maintain highly reliable supply under constrained expansion budgets and environmental policies. This can be achieved through realization of smart grid technologies and methodological advancements that would allow further improvement of asset utilization, economic operation and network security. This paper introduces a method for evaluating potential benefits as well as the technical limitations of employing dynamic thermal rating (DTR) on overhead lines (OHL) in a stressed network environment. The paper, initially models system-wide network performance under actual thermal ratings to investigate the benefits of DTR under specific operating scenarios as well as over static thermal rating (STR) on OHLs in a given network. Secondly, it investigates the benefit of implementing several additional long-term emergency rating-duration times for secure and adequate operation through a smarter ICT rule-setting program that improves network performance without compromising its reliability under contingent scenarios. The proposed methodology is employed on the IEEE 24-bus network test system suggesting a cost benefit model that balances the interests of both network operators and asset managers.

Investigating the potential of re-conductoring a lattice tower overhead line structure

In order to evaluate the potential from re-conductoring existing overhead power systems (OHL), the paper employs a holistic computational methodology that allows sag-ampacity-tension calculations considering electro-mechanical properties of arbitrary OHL systems. The focus of analysis is a 275 kV lattice tower system. Initial investigation of the performance of the widely used aluminum alloy conductors (AAAC) on this system and the comparison with the corresponding performance of the conductors on a 33-kV wood pole structure supports the conclusion that the OHL structure is an essential part of the system performance. Further analysis and results involve the mechanical and electrical performance of standard as well as some recently developed high temperature low sag (HTLS) composite conductors in order to identify the optimal conductor size and type for the investigated lattice tower system.

Modeling of Currents on Long Span, Dielectric Cables on HV Overhead Lines

It is well established that all-dielectric self-supporting cables on high-voltage overhead power lines can suffer from damage through the mechanism of dry-band arcing. A number of heuristics have evolved over the past 20 years and these are used to determine whether such cables are capable of reliable performance. A key element to planning is modeling the installation conditions. In addition to the geometry of the high-voltage line, such a model needs to consider the climatic environment and potential pollutants on the cable. In this paper, a model is built based on the commercial software current distribution, electromagnetic fields, grounding and soil structure analysis which is widely used in the power industry. The model developed is shown to be consistent with a number of previously published models. It is demonstrated that the relative sags of all-dielectric self-supporting cable and conductors are key to the severity of the installed situation. It is also shown that the towers do not need to be modeled for the most severe cases of high pollution, but are required for accuracy in medium and low pollution cases