Thermal Rating System Research Articles

Optimizing microgrid efficiency: Coordinating commercial and residential demand patterns with shared battery energy storage

The optimization of energy systems within a multi-microgrid framework, enriched by shared Battery Energy Storage Systems (BESS), has emerged as a compelling avenue for enhancing the efficiency of distributed energy networks. In response to the increasing integration of BESS in modern energy systems, this study investigates the implications of incorporating BESS within connected residential-commercial Microgrids (MGs). Unlike previous studies that primarily focused on cost and reliability, this research fills a significant gap in the literature by investigating the optimization of load demands patterns. Specifically, we explore the impact of shared BESS on load demand patterns in commercial-residential MGs. The research introduces two innovative critical load metrics, peak-to-average ratio (PAR) and demand profile smoothness (DPS), to assess the influence of BESS on demand profiles. In addition, the study explores the integration of a Dynamic Thermal Rating (DTR) system, compared to traditional fixed thermal rating systems, to further optimize the performance and efficiency of connected residential-commercial MGs enriched by shared BESS. Three distinct case studies, each comprising a commercial MG (shopping mall, hotel, and office building) paired with a residential MG, were considered. Utilizing a Firefly Algorithm (FA) for optimization, the study determines the optimized BESS capacity for minimum total cost. The results highlight that the implementation of shared BESS, especially in collaboration between commercial and residential MGs, significantly reduces imported energy from the main grid, enhancing MG flexibility and resilience. While the economic benefits of shared BESS may not be substantial (up to 3.25 % cost reduction), the study underscores its contribution to more balanced and smoother load demand curves, with improvements in PAR (up to 15.63 %) and DPS (up to26.05 %). Moreover, considering DTR for transmission lines, instead of fixed thermal rating, improves the PAR and DPS up to 28.52 % and 41.06 % respectively. The findings of this study highlight the importance of considering load demand patterns in the design and operation of MGs and underscore the multifaceted benefits of shared BESS beyond economic considerations.

A new approach for reliability assessment of the smart microgrids using k-shortest path algorithms

The reliability of cyber-physical microgrids (MGs) is crucial in the development of smart grids. The reliability of MGs can be affected by cyber network failures, which have a significant impact on the physical components. Since MGs have interdependent cyber and physical elements, a smart MG can be viewed as a system of n dependent two-mode components. This paper proposes an approach to finding the k most likely configurations of the system. The method involves three phases. Firstly, the multi-mode model is obtained for physical components, considering the operation and topology of the cyber network. Then, the problem is transformed to finding the k most likely state of a system consisting of n independent multi-mode components. In the second phase, a transformation using new transformed metrics is applied. This results in the problem being converted to finding the k shortest path, which can be solved using efficient algorithms. Finally, the states are evaluated using a DC load flow, and reliability indices such as loss of load probability (LOLP) and expected energy not supplied (EENS) are calculated. Moreover, we have incorporated the dynamic thermal rating (DTR) system into our proposed model, addressing the safe enhancement of system component ratings. The results indicate that the most probable states of the system are related to the failure of distribution generators. The most severe events occur due to failure in the cyber network, and cyber network malfunction has a higher effect on EENS compared to LOLP. Additionally, we observe a significant enhancement in reliability indices when considering the DTR system over the static thermal rating (STR) system. This approach is efficient in reliability calculation using fewer system states.

On the issue of applying the dynamic thermal rating in electric power distribution system

The article considers separate studies and review articles on dynamic thermal rating system in power transmission lines and electrical equipment. Available researches of foreign authors are mainly devoted to forecasting algorithms, model-ing methodologies and implementation of dynamic thermal rating in order to increase the capacity of power transmis-sion lines. It is shown that for the tasks of planning and management of the electric power system in Russia, the need to study and coordinate domestic and foreign developments on the assessment of the capacity of power transmission lines and power distribution is currently relevant. The expansion of residential areas increases the load on electric distribution network due to the shift of maximum power consumption. The currently dynamically changing conditions of electricity consumption direct attention to the development of new technological concepts and the applicability of the existing approaches to assessing the capacity of electricity transmission lines to distribution networks. Available research on dynamic thermal rating in electric distribution networks has focused much attention on both the potential problems and benefits of its implementation in the integration of distributed generation based on the renewable energy sources, in particular wind generation. The ambiguous impact of dynamic thermal rating systems on the reliability of the electric distribution network and the need for their reasonable use, as well as a significant lack of research in relation to cable distribution networks and consistency in assessing their capacity depending on the cable insulation material are being not-ed. Few studies have verified the adaptation of the state-of-the-art approach of dynamic thermal rating of overhead transmission lines to cable lines for predicting parameters corresponding to operational objectives. The research results can be useful in the development and modernization of metering systems, in which new functions of power loss moni-toring and automated determination of distribution network reliability indicators are implemented, which will allow, within the framework of “smart grids”, to ensure the required level of reliability of power supply to consumers.

Optimal sizing of battery energy storage systems and reliability analysis under diverse regulatory frameworks in microgrids

The integration of battery energy storage systems (BESS) with microgrids (MG) is crucial to improve the reliability and flexibility of renewable energy sources (RES) integration. However, the reliability and regulatory policies are critical factors that affect the optimal operation of MGs in the market. This study aims to enhance the reliability of MGs integrated with RES and BESS by evaluating their performance under different regulatory frameworks, namely feed-in tariff (FiT), net metering (NM), and energy storage incentive (ESI). Also, a dynamic FiT (D-FiT) framework is utilized to improve the reliability of the MG. An artificial bee colony optimization algorithm is utilized to optimize the size of BESS for each regulatory policy to minimize the total cost of the MG. Each policy is formulated based on its specific constraints in the problem. Subsequently, the reliability indices of Loss of Load Expectation (LOLE) and Expected Energy not Supplied (EENS) are calculated for each optimized solution. Moreover, we have integrated the dynamic thermal rating (DTR) system into our proposed model, focusing on the safe augmentation of system component ratings. The study finds that the D-FiT and standard FiT frameworks provide the best reliability level, whereas the reliability improvement under the ESI policy is not significant, as most of the MG's demand is supplied by the main grid. Furthermore, the study shows that the improvements in EENS are higher than LOLE, indicating that installing BESS reduces the loss of energy rather than the number of interruption hours. D-FiT framework has a significant positive impact on both reliability indices, unlike the other frameworks that have a greater effect on EENS. Furthermore, we have noticed a substantial improvement in reliability indices when the DTR system is taken into account, as compared to the static thermal rating (STR) system.

Optimisation of generation unit commitment and network topology with the dynamic thermal rating system considering N-1 reliability

The electrical grid is a vital component of modern society that requires significant and cost-effective investments to ensure its reliability. The dynamic thermal rating system (DTR) and network topology optimization (NTO) aim to increase the capacity of existing networks and provide flexible options for enhancing power system reliability. The co-optimization framework for generation unit commitment and network switching is formulated with for N-1 reliability, a gap that has not been previously addressed. This is important as it ensures: (1) economic efficiency in power system despatch, (2) optimal operation of both generation and transmission systems, and (3) power grid operation that can withstand the loss of any single component without causing a cascading failure. The reliability impacts of these new proposed operating strategies are also tested on complex, large-scale power systems under long-term, multi-area weather conditions. This proposed work is useful for power system planners, as it helps them identify ways to improve the reliability and efficiency of power systems under various weather conditions. This paper shows that using the DTR-NTO combination improves EENS by 50% in both test cases compared to the original condition. Additionally, it also makes the reliability assessment more realistic when taking into account multi-area weather conditions.

Resiliency-Oriented operation of distribution networks under unexpected wildfires using Multi-Horizon Information-Gap decision theory

Extreme events may trigger cascading outages of different components in power systems and cause a substantial loss of load. Forest wildfires, as a common type of extreme events, may damage transmission/distribution lines across the forest and disconnect a large number of consumers from the electric network. Hence, this paper presents a robust scheduling model based on the notion of information-gap decision theory (IGDT) to enhance the resilience of a distribution network exposed to wildfires. Since the thermal rating of a transmission/distribution line is a function of its temperature and current, it is assumed that the tie-line connecting the distribution network to the main grid is equipped with a dynamic thermal rating (DTR) system aiming at accurately evaluating the impact of a wildfire on the ampacity of the tie-line. The proposed approach as a multi-horizon IGDT-based optimization problem finds a robust operation plan protected against the uncertainty of wind power, solar power, load, and ampacity of tie-lines under a specific uncertainty budget (UB). Since all uncertain parameters compete to maximize their robust regions under a specific uncertainty budget, the proposed multi-horizon IGDT-based model is solved by the augmented normalized normal constraint (ANNC) method as an effective multi-objective optimization approach. Moreover, a posteriori out-of-sample analysis is used to find (i) the best solution among the set of Pareto optimal solutions obtained from the ANNC method given a specific uncertainty budget, and (ii) the best resiliency level by varying the uncertainty budget and finding the optimal uncertainty budget. The proposed approach is tested on a 33-bus distribution network under different circumstances. The case study under different conditions verifies the effectiveness of the proposed operation planning model to enhance the resilience of a distribution network under a close wildfire.

Impacts of Communication Network Availability on Synchrophasor-Based DTR and SIPS Reliability

Themodern electricity network has become smarter and more reliable because of the addition of information and communication technology. Dynamic thermal rating systems (DTR) allow existing transmission lines to be operated much closer to their limits. However, line outages after DTR implementation could threaten network security. Thus, system integrity protection schemes (SIPS), which are designed to ensure security, are useful to forestall impending contingencies that could arise from DTR implementation. Furthermore, synchrophasors can improve wide-area monitoring and protection capabilities. However, the reliability of these technologies considering their communication network availability is yet to be studied in a unified framework. Therefore, a novel framework of synchrophasor-based DTR and SIPS is presented while examining eight DTR network topologies and two SIPS schemes simultaneously. A sequential Monte Carlo simulation-based technique is proposed to simulate the effect of the topologies on system-wide reliability. This method is tested on the IEEE-RTS. Results show an improvement of 93.27% between DTR communication Schemes 1 and 8 in load curtailment. More importantly, the article reveals an improvement of 99.15% in the load curtailment value in scenarios where SIPS is deployed compared with the case where SIPS is not deployed, highlighting the benefits of DTR and SIPS hybrid implementation.

Composite Reliability Impacts of Synchrophasor-Based DTR and SIPS Cyber–Physical Systems

The integration of smart infrastructures that facilitate two-way communication via information and communication technology (ICT) has enhanced the efficiency and sustainability of the power network. However, technologies, such as dynamic thermal rating (DTR) systems and system integrity protection schemes (SIPS), have disadvantages, including infrastructure failures, cyber–physical interdependencies, and cyber intrusions. These disadvantages contribute to the reduced reliability of the network. Comprehensive exploration of the reliability impacts of multiple smart grid technologies on a single power network has not been conducted. A DTR and SIPS system integrating wide area monitoring functions using phasor measurement units (PMUs) is presented in this study, and the effect of ICT contingencies on network reliability is investigated. A Monte Carlo simulation approach and a scenario reduction technique are utilized in this article. This approach is evaluated on the IEEE-RTS to demonstrate the advantages of ICTs. The approach is suitable for different network topologies, in which the difference lies in the number of required PMUs. Results demonstrate that a reliable SIPS can minimize the aging process while slightly influencing load curtailment despite the increase in overall network aging due to DTR. PMU functional failures result in load loss due to loss of observability despite their high availability.

Fuzzy Dynamic Thermal Rating System-Based Thermal Aging Model for Transmission Lines

Electricity demand has surged over the last several years and will persist in the future. Increased transmission loads cause transmission lines to operate much closer to their security limits, leading to thermal and mechanical stress and thus affecting the transmission reliability and thermal aging. Accordingly, monitoring the conductor temperature over time is critical to identifying power transmission networks that may need extra attention and perhaps maintenance. This paper presents a fuzzy thermal aging model for transmission lines equipped with a fuzzy dynamic thermal rating system based on the IEEE 738 standard. In this framework, the ampacity of the transmission line was calculated. The conductor temperature was computed with the back-calculation method by considering the fully loaded transmission line. The estimated conductor temperature was employed to determine the corresponding conductor fuzzy loss of tensile strength, i.e., the fuzzy annealing degree of the conductor based on the Harvey model. Additionally, a tensile strength loss cost profile is provided. Simulation and numerical results indicate that the proposed framework is robust against various operating conditions of the parameters considered in the study and provides crucial information for managing transmission assets and transmission network operation.

REGIONALY IMPORTANT SINCRO.GRID SMART GRID PROJECT

Regional transmission and distribution challenges has evolved and changed a lot in recent years. Four contradictory influences increasingly affected the operations of Slovenian and Croatian electricity systems. Regional electricity systems experienced increasing support of RES integration to meet the EU targets, a lower electricity consumption due to the economic crisis, a growing lack of centralized electricity production for electric system support and the high interconnectivity between the neighboring control zones. TSOs and DSOs observed growing network overvoltage issues as well as a decrease in secondary reserve capacities. Such situation starts to impact national and regional renewable integration targets affecting the security of supply at European level. SINCRO.GRID joint investment project addressed the above-mentioned issues in a sustainable manner. Such cross-border systemic approach will bring synergetic benefits. It will enable an acceptable level of security of operation for at least the next ten years hosting levels of RES in line with the trends foreseen to reach the 2030 targets safely. The project is going to integrate new active elements in the transmission and distribution grids. It leans on the following main pillars: deployment of six compensation devices, deployment of advanced dynamic thermal rating (DTR) systems, deployment of electricity storage systems, integration of distributed renewable generation (DG) and deployment of a virtual cross-border control center (VCBCC). A key aspect of the SINCRO.GRID project lies in the synergy brought by the simultaneous innovative deployment of a portfolio of mature technology-based solutions bring high benefits and positive externalities for the region and European Union.

Demand Respond Program and Dynamic Thermal Rating System for Enhanced Power Systems

This paper reviews the development of demand response (DR) and dynamic thermal rating (DTR) system for enhancing the operation and reliability of power system. The advantages and prospect of the DR program are discussed. The case for DTR system is established by comparing it against the traditional static thermal rating (STR) system. Various line monitoring methods and devices required for the implementation of the DTR system are presented. The challenges for deploying the DTR system from the perspective of selecting appropriate transmission lines for DTR deployment, identifying critical spans for deploying DTR sensors, managing the reliability of the DTR system, and the integration of the DTR system with existing and future power systems are discussed. Finally, the two main standards governing the operation of the DTR system, namely the IEEE 738 standard and the CIGRE standard are compared to elucidate the employability of the DTR system.

Network topology optimisation based on dynamic thermal rating and battery storage systems for improved wind penetration and reliability

The nonflexible operations of transmission networks with high load demand and wind power increase the likelihood of power congestions and deteriorate grid reliability. This condition causes higher load curtailments and inhibits the penetrations of wind power, subsequently leading to higher dispatch cost because more expensive generators compensate for the loss of wind integrations. These unfavourable factors contribute to a higher total system operating cost, which should be reduced. This paper applies a network topology optimisation technique to optimise line and busbar switching for relieving network congestions and improving network flexibility. A dynamic thermal rating system is used to enhance overhead line ratings. A battery storage system is utilised to time shift wind power usage and avoid wind spillage. These methods are effective but they have been studied only in isolation. This paper presents an assessment framework that combines all the three methods in a single model to evaluate their synergistic effects on wind integration and network reliability. The proposed framework is generic and can be applied on any networks with changes only to the numerical results. The battery energy and power ratings required to maintain the prevailing security of supply standards in a large scale wind-integrated network are determined probabilistically. Case studies performed on a modified IEEE 24-bus reliability test system show that the proposed combination of methods reduces system dispatch, load curtailment and wind curtailment costs the most when compared to any combinations with fewer methods or using each method in isolation.

Dynamic thermal analysis for underground cables under continuously fluctuant load considering time-varying van wormer coefficient

With the extensive integration of renewable energy sources in power system, the fluctuation characteristics of transmission and distribution network load have been further strengthened. However, for the power cable widely used in power system, its dynamic thermal behavior under continuously fluctuant load cannot be well modeled by the IEC method. It has not been sufficiently addressed in the literatures either. In this paper, the variation of the time-dependent Van Wormer coefficient and the error cumulative phenomenon of adopting the constant Van Wormer coefficient in conventional methods (including the IEC 60853-2 and the classical thermo-electric equivalent method) under continuously fluctuant cable load are discussed. Moreover, several different modification ways on the lumped thermal model of cable insulation to mitigate the possible error cumulative phenomenon are presented. The superiority of the modified methods compared with the conventional methods is verified by the real cable experiments. The results show that the modified methods can better reflect the cable's real thermal behavior under continuously fluctuant load. The modified methods are instructive for maximizing cable utilization while still ensuring cable reliability, which can be easy to be integrated into the existing real-time cable thermal rating system.

Fuzzy Dynamic Thermal Rating System-Based SIPS for Enhancing Transmission Line Security

The increased integrations of intermittent renewable energy sources into power systems cause more power grid congestions and therefore system operators need more advanced control to relieve this pressure. The dynamic thermal rating (DTR) system is able to increase the thermal constraint and subsequently maximum loading of existing lines. This dynamic rating is achieved through real-time considerations of weather data and it is usually much higher than the traditional static thermal rating system. The operational tripping scheme (OTS), a variant of the wider system integrity protection scheme, also relieves line congestions but it does this by tripping pre-selected generators and this have the unwanted consequence of reducing power adequacy. This paper proposes the novel integration of DTR and OTS, while considering the inherent uncertainties of their sensors based on fuzzy numbers, to avoid unnecessary generation tripping due to conservative line ratings. This novel Fuzzy-DTR-OTS delays the tripping of generations, enhances the adequacy of power supply, improves system security and avoids high risk cascading black out inducing events.

A Robust Coordinated Expansion Planning Model For Wind Farm-Integrated Power Systems With Flexibility Sources Using Affine Policies

This article presents a two-stage adaptive robust coordinated generation and transmission expansion planning model for a wind farm-integrated power system. Also, dynamic thermal rating (DTR) systems, energy storage systems, and optimal line switching maneuvers are considered as various flexible sources to enhance the flexibility of the power system in response to uncertain variations of net system demand. The proposed approach characterizes the uncertainty of demands, wind power, and DTRs in each representative day by a polyhedral uncertainty set. Additionally, the k-means clustering technique is used to obtain upward/downward variations of correlated uncertain parameters in each representative day and to construct the uncertainty set. The proposed model is inherently intractable as it includes infinite constraints modeling enforced techno-economic limitations for all realizations of uncertain parameters. To resolve this limitation, the proposed intractable model is recast as a tractable mixed-integer linear programming problem using affine policies. The proposed approach is implemented on the Garver 6-bus and IEEE 73-bus test systems. Simulation results illustrate its flexibility, practicality, and tractability.

Using Dynamic Thermal Rating and Energy Storage Systems Technologies Simultaneously for Optimal Integration and Utilization of Renewable Energy Sources

Nowadays, optimal integration and utilization of renewable energy sources (RES) are of the most challenging issues in power systems. The wind and solar generation units' maximum production may or may not occur at peak consumption times resulting in non-optimal utilization of these resources. As a solution to this problem, energy storage systems (ESS) are embedded in networks. However, the power transfer from RES to ESS may lead to network congestion. In this paper, the simultaneous application of dynamic thermal rating (DTR) technology and ESS devices is proposed. The DTR is used to overcome the problem of transmission lines limited capacity and ESS is responsible for mitigating curtailment of RESs energy production by saving their generated energy in non-peak hours. The RESs generation and lines’ ratings are calculated based on hourly actual weather elements. For evaluating the proposed method, a linearized formulation of DC-OPF is used in the problem definition and also simulated on a modified IEEE 30-bus test system including a wind farm, solar park, and ESS devices by using MATLAB software. In addition, different comparisons are performed demonstrating the remarkable and better performance of the proposed method compared to previously introduced methods.

Probabilistic Peak Demand Matching by Battery Energy Storage Alongside Dynamic Thermal Ratings and Demand Response for Enhanced Network Reliability

Battery energy storage systems (BESS), demand response (DR) and the dynamic thermal rating (DTR) system have increasingly played important roles in power grids worldwide. In addition to storing energy, BESS can supply peak demands, thereby reducing the frequency of load interruptions and deferring new asset investments. However, study on the precise BESS sizing (i.e. energy and power ratings) to supply peak demands to improve the security of supply of transmission networks is still lacking. The combined efficacy of BESS, DR and DTR have also never been studied, because their simultaneous deployment has never been considered. The first contribution of this paper is proposing a probabilistic evaluation method to evaluate various combinations of BESS power ratings and energy capacities and determines their impacts on the reliability of transmission networks, in which peak demands are supported by charges stored in BESSs to address the security of supply problem. The second contribution extends the proposed method to examine the effects of deploying BESS alongside DR and DTR. Our results show that the security of power supply improves along with BESS sizing by as much as 37.2%, and that its reliability becomes more significant as its capability grows, with bigger BESS having more detrimental effects towards EENS as it becomes unavailable than smaller BESS does. DTR and DR reduce the requirements of BESS sizing without adversely affecting network reliability.

Reliability impacts of the dynamic thermal rating and battery energy storage systems on wind-integrated power networks

Abstract Increasing the penetration of wind energy in power networks is one of the ways to reduce industrial carbon footprint. However, the intermittency of wind speed inhibits the widespread installation of wind farms and hinders the share of wind energy. A way to tackle this problem is by installing a battery energy storage system (BESS) to store excess wind energy for future usage, such as when wind speed is low. The dynamic thermal rating (DTR) system is also beneficial in further enabling wind energy to be utilised and distributed to consumers by alleviating the congestion of power networks. However, despite the benefits of these technologies, the modelling of their joint reliability impacts on power networks has never been performed. This study presents for the first time the reliability modelling of the two technologies mentioned above. The models are realistic because they are based on actual weather conditions and the operating scenarios of power systems. Results show that both BESS and DTR systems can lower demand losses and increase the saved, supported and delivered wind energy depending on the settings of the two systems. Three new indices are introduced to measure wind energy-related performance.

Implementation of Quasi-Real-Time Rating Software to Monitor 525 kV Cable Systems

In 1999, BC Hydro installed optical fibers in the fluid channel of 525 kV self-contained fluid-filled submarine cables originally installed in the 1980s that connect substations in the Vancouver area of British Columbia, Canada, for the purposes of monitoring temperatures. In combination with this work, a real-time monitoring was used to collect load data and measured temperatures in an effort to optimize the ratings of the cables. The dynamic thermal circuit rating system developed by the Electric Power Research Institute was applied to the 525 kV cables as part of a project to modify the system for support of the unique characteristics of the cable system installation. Specifically, the submarine cables utilize a parallel pipe water cooling system for the shore zones. This paper describes the software modifications that were implemented to enhance the dynamic rating system to model the unique characteristics of the 525 kV cable system and discusses how recorded data collected over several seasons were used to verify and refine the cable rating model. The resulting evaluation showed good agreement of the dynamic rating system calculations with measured results and helped the utility better understand the ratings on these circuits and permitted the utility to perform simulations to evaluate various loading conditions.

Cooling of overhead power lines due to the natural convection

The development of Dynamic Thermal Rating (DTR) systems for transmission lines in recent years has led to a better and safer utilization of the existing transmission network, as it, for most cases, enables transmission capacity of lines to be increased above the traditionally used static thermal rating value, when weather conditions are favourable. Yet, on-site measurements in the Slovenian system have also shown that many sites are regularly subject to conditions of very limited or even no winds, causing the line rating to fall well below the static value. In those conditions, the natural convective cooling can surpass forced convective cooling and correctly assessing natural convective cooling becomes crucial for the Transmission System Operators (TSO). Different mathematical models deal with natural convective cooling in different ways. Moreover, references have emerged that claim that cooling due to the natural convection gives the same results as with forced convection at 0.6 m/s crossing wind. To clarify the thermal behaviour of power lines when no external wind is present, this paper employs thermo-fluid simulation of natural convection and compares it with laboratory measurements for two different conductors. The results are also compared with CIGRE, IEEE and IEC guidelines.