scholarly journals Spreading of Disturbances in Realistic Models of Transmission Grids: Dependence on Topology, Inertia and Heterogeneity

2021 ◽  
Author(s):  
Kosisochukwu P. Nnoli ◽  
Stefan Kettemann
Keyword(s):  
Geodesic Distance ◽  
Pearson Correlation ◽  
Energy Transition ◽  
Power Grids ◽  
Reliable Estimate ◽  
Time Of Arrival ◽  
Inhomogeneous Distribution ◽  
Renewable Energy Resources ◽  
Effective Distance ◽  
Heterogeneous Distribution

Abstract The energy transition towards more renewable energy resources (RER) profoundly affects the frequency dynamics and stability of electrical power networks. Here, we investigate systematically the effect of reduced grid inertia, due to an increase in the magnitude of RER, its heterogeneous distribution and the grid topology on the propagation of disturbances in realistic power grid models. These studies are conducted with the DigSILENT PowerFactory software. By changing the power generation at one central bus in each grid at a specific time, we record the resulting frequency transients at all buses. Plotting the time of arrival (ToA) of the disturbance at each bus versus the distance from the disturbance, we analyse its propagation throughout the grid. While the ToAs are found to be distributed, we confirm a tendency that the ToA increases with geodesic distance linearly. Thereby, we can measure an average velocity of propagation by fitting the data with a ballistic equation. This velocity is found to decay with increasing inertia. Characterising each grid by its meshedness coefficient, we find that the distribution of the ToAs depends in more meshed grids less strongly on the grid inertia. In order to take into account the inhomogeneous distribution of inertia, we introduce an effective distance reff, which is weighted with a factor which strongly depends on local inertia. We find that this effective distance is more strongly correlated with the ToAs, for all grids. This is confirmed quantitatively by obtaining a larger Pearson correlation coefficient between ToA and reff than with r. Remarkably, a ballistic equation for the ToA with a velocity, as derived from the swing equation, provides a strict lower bound for all effective distances reff in all power grids. thereby yielding a reliable estimate for the smallest time a disturbance needs to propagate that distance as function of system parameters, in particular inertia. We thereby conclude that in the analysis of contingencies of power grids it may be advisable that system designers and operators use the effective distance reff, taking into account inhomogeneous distribution of inertia as introduced in Eq. (11), to locate a disturbance. Moreover, our results provide evidence for the importance of the network topology as quantified by the meshedness coefficient β.

scholarly journals Spreading of disturbances in realistic models of transmission grids in dependence on topology, inertia and heterogeneity

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Kosisochukwu P. Nnoli ◽  
Stefan Kettemann
Keyword(s):  
Geodesic Distance ◽  
Pearson Correlation ◽  
Energy Transition ◽  
Power Grids ◽  
Reliable Estimate ◽  
Time Of Arrival ◽  
Inhomogeneous Distribution ◽  
Renewable Energy Resources ◽  
Effective Distance ◽  
Heterogeneous Distribution

AbstractThe energy transition towards more renewable energy resources (RER) profoundly affects the frequency dynamics and stability of electrical power networks. Here, we investigate systematically the effect of reduced grid inertia, due to an increase in the magnitude of RER, its heterogeneous distribution and the grid topology on the propagation of disturbances in realistic power grid models. These studies are conducted with the DigSILENT PowerFactory software. By changing the power generation at one central bus in each grid at a specific time, we record the resulting frequency transients at all buses. Plotting the time of arrival (ToA) of the disturbance at each bus versus the distance from the disturbance, we analyse its propagation throughout the grid. While the ToAs are found to be distributed, we confirm a tendency that the ToA increases with geodesic distance linearly. Thereby, we can measure an average velocity of propagation by fitting the data with a ballistic equation. This velocity is found to decay with increasing inertia. Characterising each grid by its meshedness coefficient, we find that the distribution of the ToAs depends in more meshed grids less strongly on the grid inertia. In order to take into account the inhomogeneous distribution of inertia, we introduce an effective distance $$r_{\mathrm{eff}}$$ r eff , which is weighted with a factor which strongly depends on local inertia. We find that this effective distance is more strongly correlated with the ToAs, for all grids. This is confirmed quantitatively by obtaining a larger Pearson correlation coefficient between ToA and $$r_{\mathrm{eff}}$$ r eff than with r. Remarkably, a ballistic equation for the ToA with a velocity, as derived from the swing equation, provides a strict lower bound for all effective distances $$r_{\mathrm{eff}}$$ r eff in all power grids. thereby yielding a reliable estimate for the smallest time a disturbance needs to propagate that distance as function of system parameters, in particular inertia. We thereby conclude that in the analysis of contingencies of power grids it may be advisable that system designers and operators use the effective distance $$r_{\mathrm{eff}}$$ r eff , taking into account inhomogeneous distribution of inertia as introduced in Eq. (12), to locate a disturbance. Moreover, our results provide evidence for the importance of the network topology as quantified by the meshedness coefficient $$\beta$$ β .

scholarly journals Spreading of Disturbances in Realistic Models of Transmission Grids: Dependence on Topology, Inertia and Heterogeneity

2021 ◽  
Author(s):  
Kosisochukwu Pal Nnoli ◽  
Stefan Kettemann
Keyword(s):  
Arrival Time ◽  
Geodesic Distance ◽  
Electrical Power ◽  
Energy Transition ◽  
Power Grids ◽  
Transmission Network ◽  
Renewable Energy Resources ◽  
Power Networks ◽  
Heterogeneous Distribution ◽  
The Times

The energy transition towards more renewable energy resources (RER) together with the reduction of conventional energy sources profoundly affects the frequency dynamics and electromechanical stability of electrical power networks. Here, we investigate the effect of different levels of grid inertia and its heterogeneous distribution on propagation patterns of disturbances in realistic models of power grids, including the Nigerian transmission network, the Ghana transmission network and the IEEE 118 bus test-grid as well as a Cayley-tree network, as a model grid without cycles, and the Square-grid power network as a strongly meshed model grid. These studies are conducted with the DigSILENT PowerFactory software and compared with results obtained from swing equations.Results show that the times of arrival of frequency deviations as function of geodesic distance from the contingency are more clustered and decay faster in more meshed grids than in tree- like or weakly meshed grids. In order to take into account the inhomogeneous distribution of inertia, we define an effective distance and find it to be more strongly correlated with the arrival time than the geodesic distance. A ballistic equation for the arrival time, with a velocity derived from the swing equation, provides then a strict lower bound for all effective distances. The fitted velocity decays with a power law with grid inertia. Decreasing the magnitude of grid inertia by increasing the magnitude of RER is thereby found to increase the travel velocity of disturbances and reduce the time a disturbance needs to spread throughout the grid.

Reliability of the Minimum Masking Level as Outcome Variable in Tinnitus Clinical Research

2020 ◽  
Vol 29 (3) ◽  
pp. 429-435
Author(s):  
Patricia C. Mancini ◽  
Richard S. Tyler ◽  
Hyung Jin Jun ◽  
Tang-Chuan Wang ◽  
Helena Ji ◽  
...  
Keyword(s):  
Standard Deviation ◽  
High Frequency ◽  
Pearson Correlation ◽  
Correlation Coefficients ◽  
Outcome Variable ◽  
Reliable Estimate ◽  
Moderate Correlation ◽  
Trained Subjects ◽  
The Relationship ◽  
Minimum Intensity

Purpose The minimum masking level (MML) is the minimum intensity of a stimulus required to just totally mask the tinnitus. Treatments aimed at reducing the tinnitus itself should attempt to measure the magnitude of the tinnitus. The objective of this study was to evaluate the reliability of the MML. Method Sample consisted of 59 tinnitus patients who reported stable tinnitus. We obtained MML measures on two visits, separated by about 2–3 weeks. We used two noise types: speech-shaped noise and high-frequency emphasis noise. We also investigated the relationship between the MML and tinnitus loudness estimates and the Tinnitus Handicap Questionnaire (THQ). Results There were differences across the different noise types. The within-session standard deviation averaged across subjects varied between 1.3 and 1.8 dB. Across the two sessions, the Pearson correlation coefficients, range was r = .84. There was a weak relationship between the dB SL MML and loudness, and between the MML and the THQ. A moderate correlation ( r = .44) was found between the THQ and loudness estimates. Conclusions We conclude that the dB SL MML can be a reliable estimate of tinnitus magnitude, with expected standard deviations in trained subjects of about 1.5 dB. It appears that the dB SL MML and loudness estimates are not closely related.

scholarly journals Transient stability analysis of power grids with admissible and maximal robust positively invariant sets

2020 ◽  
Vol 68 (12) ◽  
pp. 1011-1021
Author(s):  
Tim Aschenbruck ◽  
Willem Esterhuizen ◽  
Stefan Streif
Keyword(s):  
Power Systems ◽  
Transient Stability ◽  
Energy Transition ◽  
Power Grids ◽  
Invariant Sets ◽  
Admissible Sets ◽  
Major Fault ◽  
Bounded Disturbances ◽  
One Machine ◽  
Positively Invariant Sets

AbstractThe energy transition is causing many stability-related challenges for power systems. Transient stability refers to the ability of a power grid’s bus angles to retain synchronism after the occurrence of a major fault. In this paper a set-based approach is presented to assess the transient stability of power systems. The approach is based on the theory of barriers, to obtain an exact description of the boundaries of admissible sets and maximal robust positively invariant sets, respectively. We decompose a power system into generator and load components, replace couplings with bounded disturbances and obtain the sets for each component separately. From this we deduce transient stability properties for the entire system. We demonstrate the results of our approach through an example of one machine connected to one load and a multi-machine system.

scholarly journals The state of green energy transition in regional industrial centres—The case study of Székesfehérvár

2021 ◽  
Keyword(s):  
Renewable Energy ◽  
Local Governance ◽  
Economic Value ◽  
Value Added ◽  
Energy Transition ◽  
Local Environment ◽  
Green Energy ◽  
Urban Region ◽  
Renewable Energy Resources ◽  
Sustainable Solutions

Abstract Industrial parks may be high pollutants of the local environment, but also engines of regional development, employment, and economic value added. To make them more sustainable, regional planning often purports to promote a transition to a greener approach, but in reality, many green measures oppose business logic and profitability, while those companies that do invest in sustainable solutions do so without having a clear strategy. This complicated setup is to be explored and modelled in this article which is focused on a remarkable area, the urban region of Székesfehérvár, an industrial city in Hungary having an impressive economic development and hosting significant domestic and international companies. The disharmony between greening policies, intentions and actions is observable in Székesfehérvár, despite the considerable local and regional potentials of renewable energy resources. Findings indicate that systemic thinking and future-oriented decision making will be necessary to achieve true sustainability, which also requires a mutually proactive attitude and the cooperation of different sectors. A legitimate strategy aiming at greening the local and regional economy (with renewable energy concerns), implemented by both public and business actors can be the key element of a successful transition. This strategy needs to be stimulated by local governance.

scholarly journals Energy Storage as a System Resource

2020 ◽  
Author(s):  
Ramon Leon ◽  
Maria Camila Ochoa ◽  
Alejandro Gutierrez
Keyword(s):  
Energy Storage ◽  
Electricity Markets ◽  
Large Scale ◽  
Business Models ◽  
Power Grids ◽  
Renewable Energy Resources ◽  
Grid Resource ◽  
Electric Industry ◽  
Sustainable Business ◽  
System Resource

The origins of the electric industry can be traced back to the invention of the battery. However, Energy Storage Systems (ESS) have never been considered as a part of the electricity supply chain. Even though there has been an increase of government mandated storage investments in power grids, market driven investments are still lacking sustainable business models. Now, with the possibility that cost reductions of the technology make it viable for widespread utilization, multiple efforts have been devoted by the academia and industry to design its incorporation into electricity markets. A large majority of the proposals have been devoted to develop mechanisms for their incorporation in ancillary services markets or for arbitrage, considering storage as another market player, both still with little success in providing sustainable benefits to energy consumers and investors alike. In this paper, we demonstrate that Large Scale Energy Storage excels when incorporated as a service provider in electricity markets. Our proposal considers ESS as a grid resource, available to the ISO to achieve the optimal mix of resources in the day ahead dispatch. We demonstrate that in the Colombian system, a large ESS used in this manner may achieve high benefit-cost ratios. The results also indicate that current market designs need to evolve in order to take better advantage of energy storage and renewable energy resources.

What is the most accurate substitute for an invisible T1 slope in cervical radiographs? A comparative study of a novel method with previously reported substitutes

2021 ◽  
pp. 1-7
Author(s):  
Brian J. Park ◽  
Colin J. Gold ◽  
Royce W. Woodroffe ◽  
Satoshi Yamaguchi
Keyword(s):  
Linear Regression ◽  
Direct Method ◽  
Pearson Correlation ◽  
Regression Modeling ◽  
Reliable Estimate ◽  
Horizontal Line ◽  
T1 Slope ◽  
C7 Slope ◽  
Novel Method ◽  
Linear Regression Modeling

OBJECTIVE The ability to utilize the T1 slope is often limited by poor visibility on cervical radiographs. The C7 slope has been proposed as a reliable substitute but may have similar limitations of visibility. Herein, the authors propose a novel method that takes advantage of the superior visibility on CT to accurately substitute for the radiographic T1 slope and compare the accuracy of this method with previously reported substitutes. METHODS Lateral neutral standing cervical radiographs and cervical CT scans were examined. When the T1 slope was clearly visible on radiographs, the C3–7 slopes and T1 slope were measured. In CT method 1, a direct method, the T1 slope was measured from the upper endplate of T1 to the bottom edge of the CT image, assuming the edge was parallel to the horizontal plane. In CT method 2, an overlaying method, the T1 slope was calculated by superimposing the C7 slope angle measured on a radiograph onto the CT scan and measuring the angle formed by the upper endplate of T1 and the superimposed horizontal line of the C7 slope. A Pearson correlation with linear regression modeling was performed for potential substitutes for the actual T1 slope. RESULTS Among 160 patients with available noninstrumented lateral neutral cervical radiographs, the T1 slope was visible in only 54 patients (33.8%). A total of 52 patients met the inclusion criteria for final analysis. The Pearson correlation coefficients between the T1 slope and the C3–7 slopes, CT method 1, and CT method 2 were 0.243 (p = 0.083), 0.292 (p = 0.035), 0.609 (p < 0.001), 0.806 (p < 0.001), 0.898 (p < 0.001), 0.426 (p = 0.002), and 0.942 (p < 0.001), respectively. Linear regression modeling showed R2 = 0.807 for the correlation between C7 slope and T1 slope and R2 = 0.888 for the correlation between T1 slope with the CT method 2 and actual T1 slope. CONCLUSIONS The C7 slope can be a reliable predictor of the T1 slope and is more accurate than more rostral cervical slopes. However, this study disclosed that the novel CT method 2, an overlaying method, was the most reliable estimate of true T1 slope with a greater positive correlation than C7 slope. When CT studies are available in patients with an invisible T1 slope on cervical radiographs, CT method 2 should be used as a substitute for the T1 slope.

Global Energy Cultures of Speed and Lightness: Materials, Mobilities and Transnational Power

2014 ◽  
Vol 31 (5) ◽  
pp. 127-154 ◽  
Author(s):  
Mimi Sheller
Keyword(s):  
Material Culture ◽  
Energy Transition ◽  
Power Grids ◽  
Figured Worlds ◽  
Aluminum Production ◽  
Industrial Complex ◽  
Production And Consumption ◽  
Production And Distribution ◽  
History Of ◽  
The Military

Following aluminum as part of a material culture of speed and lightness, this article examines how assemblages of energy and metals connect built environments, ways of life, and ideologies of acceleration. Aluminum can be theorized as a circulatory matrix that forms an energy culture. Through a discussion of speed and social justice, the history of aluminium-based socioecologies reveals how the materiality of energy forms assemblages of objects, infrastructures, and practices. The article then traces the aluminum industry’s involvement in the production and distribution of energy itself both at the national scale of power grids and in the emergence of transnational transfers of energy, such as hydropowered smelters in Iceland. Finally, this analysis of deeply embedded energy cultures calls for a transnational approach to the accelerated socioecologies of aluminum production and consumption; and for energy transition theories to pay closer attention to the figured worlds and figuring work of the military-industrial complex.

scholarly journals A Review of Key Performance Indicators for Building Flexibility Quantification to Support the Clean Energy Transition

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5676
Author(s):  
Girolama Airò Farulla ◽  
Giovanni Tumminia ◽  
Francesco Sergi ◽  
Davide Aloisio ◽  
Maurizio Cellura ◽  
...  
Keyword(s):  
Performance Indicators ◽  
Renewable Energy Sources ◽  
Energy Transition ◽  
Clean Energy ◽  
Key Performance Indicators ◽  
Electric Power System ◽  
Power Grids ◽  
Current Status ◽  
Future Perspective ◽  
The Stability

The transition to a sustainable society and a carbon-neutral economy by 2050 requires extensive deployment of renewable energy sources that, due to the aleatority and non-programmability of most of them, may seriously affect the stability of existing power grids. In this context, buildings are increasingly being seen as a potential source of energy flexibility for the power grid. In literature, key performance indicators, allowing different aspects of the load management, are used to investigate buildings’ energy flexibility. The paper reviews existing indicators developed in the context of theoretical, experimental and numerical studies on flexible buildings, outlining the current status and the potential future perspective. Moreover, the paper briefly reviews the range of grid services that flexible buildings can provide to support the reliability of the electric power system which is potentially challenged by the increasing interconnection of distributed variable renewable generation.

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