Optimal generation units start-up sequence during restoration of power system considering network reliability using bi-level optimization

Guest Editorial: Situational awareness of integrated energy systems

This paper considers voltage control in restoration of EHV power systems. Restoration of a power system is performed by energizing transmission lines sequentially from initial power sources. These operations have already been programmed into an expert system developed by the authors. However, energizing no‐load transmission lines causes some bus voltages to rise 20 percent more than rated voltages, and transformers can tolerate a 20 percent voltage rise only for 1 min.Here, the expert system is supplemented with a function for checking bus voltages and reactive powers of initial sources, and which automatically switches on reactors. Conditions for switching reactors and selecting appropriate reactors are written by rules, hence they are easy to modify. The target of voltage control is to keep bus voltages with in ±5 percent, and to keep reactive powers of generators within 30 percent of generator capacity. Applying this method to three basic restoration patterns of a model power system shows that small adjustment of switching conditions is sufficient for two patterns, and some modification of the restoration procedure is necessary for the other pattern to obtain good voltage profiles through the restoration process.

The power system experiences many changes, which are leading to new challenges. The electric energy will no longer be generated only by large power plants, but rather by numerous decentralized energy resources that are primarily installed in distribution grids. In particular, power system restoration processes after a blackout will face new challenges. However, new opportunities by the widespread use of renewable energy resources arise. In this paper, the black start capability of a real distribution grid in Germany, operated by SWW Wunsiedel, will be investigated, as it has a high share of decentralised energy resources and a BESS with black start capability. For this purpose, the medium voltage level of the distribution grid is investigated with static load flow simulations to evaluate the best black start strategy. The driving forces of this black start concept are an 8 MW BESS unit and a 13.5 MW CHP plant.

Power system restoration is the procedure of restoring a power system after a blackout and different strategies have developed for it because of its importance. One of the most practical and economical strategies is a "Build-up strategy" that includes the process of restoring separated islands in the power system and interconnecting them after it. The process of Build-up power system restoration is highly affected by power system telecommunication capabilities. Based on the constraints of wide area measurement system (WAMS) operation, each island must be fully observable. This paper provides an approach for power system restoration and observability of these islands. The New England 39 bus power system has used to simulate the presented approach. Copyright © 2010 John Wiley & Sons, Ltd.

Restoring a large-scale power system has always been a complicated and important issue. A lot of research work has been done on different aspects of the whole power system restoration procedure. However, more time will be required to complete the power system restoration process in an actual situation if accurate and real-time system data cannot be obtained. With the development of the wide area monitoring system (WAMS), power system operators are capable of accessing to more accurate data in the restoration stage after a major outage. The ultimate goal of the system restoration is to restore as much load as possible while in the shortest period of time after a blackout, and the restorable load can be estimated by employing WAMS. Moreover, discrete restorable loads are employed considering the limited number of circuit-breaker operations and the practical topology of distribution systems. In this work, a restorable load estimation method is proposed employing WAMS data after the network frame has been reenergized, and WAMS is also employed to monitor the system parameters in case the newly recovered system becomes unstable again. The proposed method has been validated with the New England 39-Bus system and an actual power system in Guangzhou, China.

The restoration of the bulk power system after a partial or complete blackout relies on black-start (BS) resources. To prepare for system restoration, it is important to procure the right amount of BS resources at the right locations in the grid so that the total restoration time can be minimized. Achieving this goal requires that resource procurement planning takes the restoration process into account. In this study, we integrate the BS resource procurement decision with a restoration planning model and develop an optimization model that produces a minimal cost procurement plan that satisfies the restoration time requirement.

The integration of ICT into power systems has increased the interdependencies between the two systems. The operation of power system depends on several ICT-enabled grid services which manifest the interdependencies. ENTSO-E system state classification is a tool that is widely used by operators to determine the current operational state of the power system. However, it does not adequately describe the impact of ICT disturbances on the operation of the power system. Despite their interconnections, the operational states of both systems have been described separately so far. This paper bridges the well-established ENTSO-E systems state classification with an ICT system state classification, forming a new model considering the state classification of the ICT-enabled grid services. The model is developed by first identifying the ICT-enabled services, remedial actions and the respective performance requirements that are required by the power system. Then the states of these services are specified based on the supporting ICT system. The resulting joint state description shows how performance degradation of ICT-enabled services (introduced by disturbances) can affect the operation of the interconnected power system. Two case studies of such ICT-enabled services, namely state estimation and on-load tap changer control, are investigated in terms of how their operational states affect the states of the power system. A third case study highlights the interdependencies that exist between the services. These case studies demonstrate the interdependencies that exist between power and ICT systems in modern cyber-physical energy systems, thus highlighting the usage of a unified system state description.

Integrated model and automatically designed solver for power system restoration

As power systems grow in their size and interconnections, their complexity increases. Rising costs due to inflation and increased environmental concerns has made transmission, as well as generation systems be operated closer to design limits. Hence power system voltage stability and voltage control are emerging as major problems in the day-to-day operation of stressed power systems. For secure operation and control of power systems under normal and contingency conditions it is essential to provide solutions in real time to the operator in energy control center (ECC). Artificial neural networks (ANN) are emerging as an artificial intelligence tool, which give fast, though approximate, but acceptable solutions in real time as they mostly use the parallel processing technique for computation. The solutions thus obtained can be used as a guide by the operator in ECC for power system control. This paper deals with development of an ANN architecture, which provide solutions for monitoring, and control of voltage stability in the day-to-day operation of power systems.

Contingency ranking is one of the methods used in power system operations and planning to foresee the behavior of a system when there is a large disturbance in the system. Several indices have been proposed in the literature for estimating the severity of a particular contingency but mostly in the area of static security assessment. Therefore, in order to effectively capture the performance of a large power system under contingencies, dynamic security assessment (DSA) indices would be more desirable. In this paper, a score is presented with relatively less computational burden and used to determine the severity of a large disturbance in the power system for the purpose of contingency ranking. This score is formulated from the algebraic state variables that are related to the machines in a multi-machine power system modeled with differential algebraic equations (DAE). The proposed score is used with the angle stability criteria and applied on the IEEE 14-Bus test system in Matlab environment to determine the critical transmission lines in the system.

Gerilim kararlılığı, güç sistemlerinde incelenmesi gereken önemli bir konudur. Sürekli artan elektrik enerjisi talebi, artan talebi karşılamak için yeni elektrik üretim santrallerinin kurulumu ve güç sistem arızaları gerilim kararlılığını olumsuz yönde etkilemektedir. Günümüzde gerilim kararlılığını iyileştirmek için güç sistemlerinde Esnek Alternatif Akım İletim Sistemleri (FACTS cihazları) kullanılmakta olup, ayrıca enerji talebini karşılamak ve gerilim kararlılığını iyileştirmek için güç sistemlerine Dağıtık Üretim Kaynakları (DGs) entegre edilmektedir. Bu çalışmada, IEEE 30 baralı güç sistemi ile Kuzeybatı Anadolu (KBA) güç sistemi, gerilim kararlılığı bakımından temel (nominal), aşırı yüklenme ve hat kopması durumlarında incelenmiştir. İncelenen güç sistemlerine FACTS cihazlarından Statik Var Kompanzatör (SVC) ve Tristör Kontrollü Seri Kapasitör (TCSC), DGs’lerden ise Yakıt Hücresi (YH), Güneş Enerji Santrali (GES) ve Rüzgâr Enerji Santrali (RES) ayrı ayrı ve birlikte bağlanmıştır. Güç sistemlerinin bara gerilim değerlerinde ve yüklenme parametresinde meydana gelen değişimler analiz edilmiştir.

Electric power systems are subject to severe damages caused by high impact low probability events such as wildfires. The effects of wildfire threats on power systems operation include power outages and economic losses. As a critical infrastructure, power systems are expected to estimate these events in order to reduce inherent risks, but the estimation of wildfire occurrence is an irksome task given its highly stochastic nature and relatively low probability of occurrence. This paper leverages the advancements offered by data availability and deep learning techniques to propose an empirical, gridded, spatio-temporal approach, as opposed to the conventional utility approach of wildfire threat areas and levels, towards more granular estimation of the probability of wildfire occurrence. Historical ignition points and diurnal weather-predictor data from 1996 to 2016 were collected, preprocessed and features extracted as training data for quantitative analysis. The fire spread is modeled as a function of wind speed and landuse data. The risk optimization of the power system is then demonstrated using the IEEE 24-bus test system.

Minimizing power loss and improving voltage stability are crucial aspects of power systems, driven by transmission line contingencies, financial losses for utilities, and potential power system blackouts. Optimal allocation comprising the sizing and operating power factor—of Distributed Generation (DG) units and capacitor banks (CBs) significantly enhances power system efficiency. Efforts by power system operators and researchers focus on addressing issues related to power loss, energy loss, voltage profiles, and voltage stability through the strategic placement of DGs and CBs. Additionally, optimal DG and CB allocation protects the distribution system from unforeseen events and enables operators to run the system in islanding mode when necessary. The integration of DG units and CBs in distribution systems aims to enhance overall system performance. This research paper introduces a Water Cycle Algorithm (WCA) for the optimal placement and sizing of DGs and CBs. The proposed method targets both technical and economic benefits, considering multiple objective functions: minimizing power losses, reducing voltage deviation, lowering total electrical energy costs, and improving the voltage stability index. The WCA emulates the natural water cycle, from streams to rivers and rivers to the sea. Five different operational scenarios are evaluated to test the performance of this methodology. Simulations are conducted on distribution systems: the IEEE 69-bus test system and the Sankhu feeder network, a real system. The results demonstrate the superior performance of the proposed WCA compared to other optimization algorithms. The findings highlight the WCA's flexibility, efficiency, and significant improvements in economic benefits, establishing it as a promising approach for optimizing the placement of DG and CB in distribution systems.

The application of unified power flow controller (UPFC) has become an inevitable trend to deal with challenges faced by modern power system such as optimization of power supply and system operation. However, review researches on UPFC are less while the researches on specific technologies mostly focus on theoretical fields, which are difficult to guide actual engineering. To this end, this paper discusses several key issues of UPFC in its actual application. First of all, technical process of UPFC in actual application was proposed and its six key issues were pointed out. Then, for three issues in the process of “scheme-obtaining of UPFC application”, the principles of necessity to configure UPFC, the method of determining UPFC location and capacity, the method of determining UPFC control strategy are discussed. Finally, for three issues in the process of “influence analysis and optimization for UPFC”, simulation calculation method of power system with UPFC, influences of UPFC on power system operation, changes strategy of operating parameter for UPFC are discussed. The work done in this article aims to provide a reference for the actual application of UPFC.

Modern power system is a typical cyber-physical system (CPS). The stable operation of the modern power system relies increasingly on the well-functioning cyber system. Therefore, it is important to include the possible effects of the cyber system as we assess power system stability. Since our main purpose of considering the cyber system is to study its possible effect on power system operation, and cyber system mainly affect the physical system through affecting the information flow, we mainly focus on the information flow as we model the cyber system. In the proposed model, the details in cyber system operation is not considered to reduce redundant calculation burden. Instead, cyber elements and cyber contingencies are classified and modeled based on their effect on the information flow, reflecting their possible effect on the operation of the power system. We can simulate the CPS by integrating the proposed cyber system model with the power system model and conducting mixed simulation. Case study is carried out in the AVC system in the IEEE-14 bus power system. The result shows the proposed cyber system model and CPS simulation method can be used to analysis the possible effect of cyber contingencies on the power system.