Transmission System Operators Research Articles

Learning Data-Driven Stable Corrections of Dynamical Systems—Application to the Simulation of the Top-Oil Temperature Evolution of a Power Transformer

Many engineering systems can be described by using differential models whose solutions, generally obtained after discretization, can exhibit a noticeable deviation with respect to the response of the physical systems that those models are expected to represent. In those circumstances, one possibility consists of enriching the model in order to reproduce the physical system behavior. The present paper considers a dynamical system and proposes enriching the model solution by learning the dynamical model of the gap between the system response and the model-based prediction while ensuring that the time integration of the learned model remains stable. The proposed methodology was applied in the simulation of the top-oil temperature evolution of a power transformer, for which experimental data provided by the RTE, the French electricity transmission system operator, were used to construct the model enrichment with the hybrid rationale, ensuring more accurate predictions.

Joint Control Strategy of Energy Storage System and Cutting Machine for Transient Stability of Direct Current Locking Rear Delivery Terminal System

With the gradual operation of large-capacity HVDC transmission, HVDC), the characteristics of the “strong and weak communication” of the power grid are increasingly obvious. The power impact of the DC line after locking has a great impact on the power angle stability of the system and seriously threatens the transient stability of the delivery end system. By establishing the equivalent model of the AC/DC system with the energy storage power station and analyzing the transient process after DC locking, we propose a control strategy for the transient stability of the energy storage system and the delivery system after DC locking. This strategy controls the charge and discharge of the energy storage system by collecting real-time power angle and voltage data of the grid, uses the equal area rule, and initiates the cutting machine after the energy storage system is withdrawn. To verify the validity and correctness of the proposed method, a simulation analysis was performed in a modified cross-flow CEPRI-36 node AC–DC system.

Frequency regulated transmission-reflection integration modes of a terahertz metasurface.

The conventional transmission and reflection operating mode switching metasurface depends on phase change materials, which are often difficult to integrate with metasurface devices and work in real time. Here, we propose an integration of a transmission-reflection metasurface that can dynamically control beam direction and functions in both transmission and reflection modes by varying the frequency of the incident wave. Remarkably, the transmission and reflection modes of terahertz beam manipulation can be obtained by illuminating only the transmission side of the metasurface. The full-wave simulation results are in good agreement with the theoretically calculated results, which verifies the terahertz wave manipulation capability of the proposed structure. This metasurface provides a design method for full-space terahertz beam regulation devices.

A Hierarchical Maintenance Method for Power System Transmission and Substation Multi-Equipment Operation Status Considering Equipment Service Age

The current conventional maintenance methods for transmission and substation operation equipment are mainly used to extract fault data features by combining micro-network algorithms to process equipment operation data. The lack of effective analysis of equipment fault characteristics leads to poor maintenance results. In this regard, a power system transmission and substation multi-device operation status hierarchical maintenance method considering the age of equipment service is proposed. By accessing the configuration network and interacting with the grid intelligent collection of data, network storage and parallel processing of data are realized. The characteristics of transmission and substation equipment operation data are analyzed and processed to build the maintenance system. In the experiments, the proposed method is validated for the effect of condition assessment. The experimental results show that when the proposed method is used to process the transmission and substation equipment, the condition assessment accuracy is high and it has a more desirable equipment maintenance performance.

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.

Assessing Hardware in the Loop Approaches for Wide-Area Monitoring Control and Protection Devices

Wide-area monitoring, protection, and control (WAMPAC) systems are expected to support the transmission system operators in maintaining stability and security of supply in the future power systems. The WAMPAC solutions heavily rely on deployment and use of phasor measurement units (PMU) and related communication technologies. Laboratory testing in a realistic environment utilizing hardware in the loop (HIL) approaches can be successfully used to evaluate WAMPAC functionalities algorithms and to accelerate proofs of concept. However, different implementations of the HIL testing can be adopted and their inherent characteristics affect both the accuracy of the results and the overall testing capabilities. The objective of this paper is to provide a comparative assessment of three HIL approaches for laboratory testing of WAMPAC systems and devices. These testing approaches have been implemented in a laboratory configuration and applied to characterize WAMPAC devices. Moreover, methodologies to quantify the error introduced by these testing approaches in static and dynamic conditions are presented and applied to this laboratory configuration.

An Impulse Aging Assessment Method for Arrester Under Multiple Strokes Based on Frequency Domain Dielectric Spectroscopy

Multiple strokes (MS) is the primary factor leading to the failure of electrical equipment. Arrester, as the critical lightning protective instrument, its service status is directly relevant to the stability of transmission system operation. Meanwhile, MS also significantly accelerates the impulse aging of arresters and ultimately causes malfunction. This paper proposes a method to evaluate the impulse aging of arresters under MS based on frequency domain dielectric spectroscopy (FDS). Firstly, MS experiments are performed, and then the FDS parameters of arresters are measured. Subsequently, the improved Havriliak–Negami equation (IHNE) is developed to explicitly analyze the dielectric relaxation process of arresters. Additionally, an improved metaheuristic algorithm is presented to identify the parameters in IHNE based on FDS, which has significant parameter identification. Eventually, the impulse aging evaluation model is established. Simultaneously, the condition of two types of arresters (including new and used arrester in service on transmission lines) are estimated based on the evaluation method presented in this paper. The maximum absolute errors are 0.73 times and 1.2 times, respectively, fully validating the effectiveness of the presented method. The investigation of this paper can provide a direct foundation for the replacement and overhaul of line arresters.

Reactive power management: Comparison of expert‐based and optimization‐based approaches for dispatcher training

AbstractReactive power management (RPM) in electric power systems is usually based on a rule‐based control derived from the transmission system operator's (TSO) experience. This approach faces challenges as the number of decisions and the complexity of the system operation is increasing. With the increasing generation from renewables and the evolution of electricity markets, the available resources must be optimally utilized. This paper compares the optimization‐based approach (OBA) and the experience‐based expert approach (EBA) for RPM. The OBA is based on security‐constrained optimization with minimum redispatch cost as the objective function for a reference contingency. In contrast, the EBA's actions are based on the system operator's experience. Comparison is made in terms of the generator redispatch cost, active and reactive power redispatch volume, active power losses, nodal voltages, and the number of actions to ensure secure operation. The analysis using a reduced model of an actual transmission system shows that OBA is more beneficial than EBA, with up to 22% and 42% reduction in redispatch cost and volume, respectively. Moreover, the control decisions from both approaches are seen to be similar. This study aims to show the usefulness of the OBA and motivate TSOs to move towards optimization‐based reactive power management.

Fully parallel decentralized load restoration in coupled transmission and distribution system with soft open points

Collaboration between transmission and distribution system operators (TSOs and DSOs) is crucial to improve power supply reliability during a massive blackout. However, these two systems usually operate separately in reality. To coordinate them, a new fully parallel decentralized TSO + DSO service restoration (D-TDSR) scheme is proposed in this paper. Based on analytical target cascading (ATC) method, the proposed D-TDSR is able to formulate the local restoration model for each TSO and DSO by decomposing shared boundary information in an iterative process. By introducing the diagonal quadratic approximation in ATC, all local restoration models are solved in a fully parallel manner with no need for a central coordinator. This parallel implementation increases the computation efficiency of decentralized restoration procedure. Furthermore, to enhance the ability of TSO and DSOs to support each other, the potential benefits of flexible regulation in DSO, including soft open points and network reconfiguration, are fully exploited, thus improving critical load restoration speed, and reducing voltage deviations. The effectiveness of the proposed D-TDSR is validated using an IEEE standard test system.

Continuous estimation of power system inertia using convolutional neural networks

Inertia is a measure of a power system’s capability to counteract frequency disturbances: in conventional power networks, inertia is approximately constant over time, which contributes to network stability. However, as the share of renewable energy sources increases, the inertia associated to synchronous generators declines, which may pose a threat to the overall stability. Reliably estimating the inertia of power systems dominated by inverted-connected sources has therefore become of paramount importance. We develop a framework for the continuous estimation of the inertia in an electric power system, exploiting state-of-the-art artificial intelligence techniques. We perform an in-depth investigation based on power spectra analysis and input-output correlations to explain how the artificial neural network operates in this specific realm, thus shedding light on the input features necessary for proper neural-network training. We validate our approach on a heterogeneous power network comprising synchronous generators, static compensators and converter-interfaced generation: our results highlight how different devices are characterized by distinct spectral footprints - a feature that must be taken into account by transmission system operators when performing online network stability analyses.

Analysis and general calculation of DC fault currents in MMC-MTDC grids

The short-circuit fault of MMC-MTDC has great influence on the safe and stable operation of the MMC-HVDC transmission system. To analyze the changing trend of short-circuit current after fault, this paper studies the short-circuit fault mechanism based on the analytical formula of MMC short-circuit current, and analyzes the influence of capacitance, inductance and resistance on short-circuit current. Subsequently, the discharge characteristics of each converter station in multi-terminal complex power grid under different fault conditions are investigated. Based on the above research, a general calculation method for short-circuit current of multi-terminal complex direct power grid is proposed. Then, a four-terminal power grid and a six-terminal power grid are built based on the PSCAD/ EMTDC electromagnetic transient simulation platform to verify the fault characteristics of MMC and discharge characteristics of multi-terminal network converter stations respectively. Finally, a digital-physical hybrid simulation experiment platform is erected to verify the effectiveness of the analytical calculation method for short-circuit current. The results demonstrate that the theoretical solution method can accurately characterize the fault current variation trend, which has an extremely important guiding significance for the engineering design and control protection of MMCHVDC transmission network.

Application of fully automated centralized voltage regulation in transmission system operation management

The influence of wind farms, inclusion of distributed energy and the energy market has a large impact on the voltage profile in a transmission system. The Croatian Transmission System Operator HOPS has implemented VVC (Volt Var Control) system which was one of the subprojects included in the EU co-founded Sincro.Grid smart grid project that was financed by the EU CEF fund. The main goal of the project is to raise voltage quality in the transmission network. VVC system is an optimal power flow-based application which calculates the optimal solution regarding the desired objective function, available control variables and a defined set of constraints. To achieve the calculated optimal power system state, control of field devices is included in the process of optimization by shifting tap changer positions or changing setpoint values of reactive power injection. Voltage and reactive power constraints are set accordingly to available regulating devices included in the optimization.
 The lack of automatic coordination of reactive power resources motivated this work for implementing an advanced VVC for real time control of reactive power in partially automatic and fully automatic (closed loop) mode using the optimal power flow (OPF) algorithm. Due to its complexity, the closed loop approach of reactive power regulation is rarely used in the TSO community and the HOPS is one of the first TSOs that implemented regulation in such manner. Except fully automatic mode of operation, VVC can be used in semi-auto or manual mode. For a successful implementation several safety algorithms are implement to avoid many unwanted situations in the power system such as voltage breakdown, overloading of regulating equipment and similar

Drawing the line: Opening up and closing down the siting of a high voltage transmission route in the Netherlands

This paper describes the decision-making process regarding the siting of a high voltage transmission line in the southern part of the Netherlands by TenneT, the Transmission System Operator responsible for the electricity infrastructure. TenneT started this siting process by deploying conventional decision-making procedures, which have the tendency centrally to pre-scope, and select the technical, spatial and societal characteristics of such projects. Following the resistance of activist groups and local authorities, a new siting process was set up based on community engagement (CE) and the upfront involvement of local stakeholders, so to include new frames and perspectives and by reconsidering the workings of standard procedures. With that, TenneT opened up decision-making processes. In our paper, we will identify the practical and institutional tensions and challenges that emerged from these attempts to ‘open up’. The work is based on an ‘inside out’ description of the case: one of the researchers undertook an ethnographic study of the siting process, while the employees of TenneT directly involved in the siting process have been invited as co-authors, so to add details and the reflections of practitioners.

A Cost–Benefit Analysis Framework for Power System Resilience Enhancement Based on Optimization via Simulation Considering Climate Changes and Cascading Outages

Achieving a good level of resilience to extreme events caused by severe weather conditions is a major target for operators in modern power systems due to the increasing frequency and intensity of extreme weather phenomena. Moreover, regulatory authorities are pushing transmission and distribution operators to prepare resilience plans suitably supported by Cost–Benefit Analyses (CBAs). In this context, this paper proposes a CBA framework based on Optimization via Simulation (OvS) for the selection of the optimal portfolio of resilience enhancement measures. Starting from a comprehensive set of candidate grid hardening and operational measures, the optimal mix is identified by applying a novel two-step procedure based on an efficient application of the generalized pattern search heuristic technique. Risk indicators for the CBA are quantified, accounting for probabilistic models of climate changes. Moreover, the potential cascading outages due to multiple component failures provoked by extreme events are simulated on selected scenarios. The examples carried out on an IEEE test system show the effectiveness of the approach in identifying the best portfolio of resilience enhancement measures depending on climate change projections and costs of the measures, while the application to the model of a large portion of the Italian EHV transmission system demonstrates the practicability of the approach in real-world studies to support operators in different power system management phases, from planning to operation.

Resilient planning for high‐renewable‐integrated transmission systems under the impacts of ice storm disasters

AbstractIce storm disasters pose great challenges to the safe and stable operation of transmission systems, especially in high‐renewable‐integration scenarios. However, as one of the major types of natural disasters that can have severe consequences, ice storm disasters are much less studied than hurricanes and earthquakes. Ice storm disasters are characterized by a long duration and wide scope, which affect the source, network, and load side of the power grid. It is difficult to formulate a quantitative evaluation of resilience and establish effective planning strategies. Here, a resilient planning method considering the interactive effects of ice disasters on sources, networks, and loads is therefore proposed. First, the two‐stage Monte Carlo method is used to generate multiple grid fault scenarios for different levels of ice storm disasters. Then, an index is proposed to quantify the grid resilience as the total amount of system power loss caused by ice storm disasters. Based on this approach, a two‐layer mathematical model is established with grid resilience and total investment cost objectives in each fault scenario. Hierarchical reinforcement and the protection of generating units and transmission lines are selected as investment strategies to mitigate the impact of ice storm disasters. Finally, the IEEE‐24 node transmission system is used to verify the feasibility and effectiveness of the proposed method. Optimizing the planning strategy can significantly improve system resilience with minimal investment cost.

On Connected Autonomous Vehicles With Unknown Human Driven Vehicles Effects Using Transmissibility Operators

This study proposes an algorithm for fault detection and mitigation of mixed autonomous and human-driven vehicle platoons based on transmissibility identification. This work is motivated by the fact that on-road human-drivers&#x2019; behaviour is unknown and difficult to be predicted. Transmissibility operators are mathematical operators that relate one subset of outputs to another in the same system. The transmissibility superiority is represented in the in-dependency on the system excitation signals. We reformulate the system dynamics to render the system inputs, external disturbances, as well as the human-drivers&#x2019; behaviour along with any other nonlinearities as independent excitation signals on the system. Therefore, the transmissibility operators become independent of the human-drivers&#x2019; behaviour and robust against external disturbances. Transmissibilities are then applied to detect and localize physical and cyber faults within the platoon. Then these faults are mitigated using a transmissibility-based sliding mode controller. The controller stability and the string stability are investigated while the controller is active and the faults are mitigated. We validate the proposed algorithm on a model of the platoon obtained using the bond graph approach. Moreover, we apply the proposed algorithm experimentally to a platoon consisting of three robots (i.e. two autonomous robots and a human-driven robot), that is connected using wireless communications. <i>Note to Practitioners</i>&#x2014;The existence of connected autonomous vehicles depends greatly on the smooth transition between the current on-road human-driven vehicles to autonomous vehicles. The typical methods of securing dynamic systems depend on estimating the system behaviour and responses. Increasing the number of autonomous vehicles on roads necessitates the typical securing techniques to estimate the human-drivers&#x2019; behaviour. Thus, securing the connected autonomous vehicles during this transition is challenging since the on-road human-driver behavior is unknown and difficult to be estimated. Moreover, connected autonomous vehicles should adapt to their environment while maintaining their role within the autonomous platoon. This adaptation includes adapting to the unknown human-driver behaviour. This inspired the authors to develop the proposed transmissibility-based fault mitigation. The proposed technique is shown to be able to handle unknown human-driver behaviors, different driving conditions such as road irregularities and different weather conditions, and different physical and cyber faults (i.e., in the vehicles or in the communication links). The platoon stability is then investigated while the faults are mitigated, and shown to guarantee the platoon stability.

A Benchmark and Validation Guide for the Hungarian Implementation of the Common European Requirements for Electricity Generators

In the Hungarian electricity system, as well as in other European countries, the share of renewable based production is increasing. These power generating modules do not contain rotating masses like those of traditional synchronous power generating modules which creates new challenges on the electric grid with respect to system stability and frequency control. The distribution system operators (DSOs) of the different countries need to cope with this problem and set frequency, voltage thresholds and robustness requirements for the electricity generating power plants. This project aims to create specific requirements for the Hungarian generators considering the former implementations of other countries (UK, Germany, Denmark and Finland). The different requirements of these foreign areas are introduced in a benchmark study, which is the first essential part of the whole project. Such implementations are only partially defined for Hungary; therefore, in some cases it is necessary to use the implementations of other foreign countries which have similar grid characteristics and are dealing with the same control and operation challenges. Another important milestone of this work besides the benchmark study is to present a validation guide for the Hungarian transmission system operator (TSO) that can be sent directly to the operators of electric power generating modules with six different types. These guides contain compliance tests for the power plants to examine whether they meet the requirements of grid connection or not.

Transition to Digitalized Paradigms for Security Control and Decentralized Electricity Market

Digitalization is one of the key drivers for energy system transformation. The advances in communication technologies and measurement devices render available a large amount of operational data and enable the centralization of such data storage and processing. The greater access to data opens up new opportunities for a more efficient and decentralized management of the energy system. At the distribution level of the energy system, local electricity markets (LEMs) provide new degrees of flexibility by trading and balancing the energy locally and offering ancillary services to the wider transmission and distribution system operators. Maximizing the grid impact from this flexibility calls for novel data analytics and artificial intelligence techniques to enhance the system's security and reduce the energy costs of local prosumers. At the same time, however, relying on data-based approaches increases the risk of cyberattacks, and robust countermeasures are, therefore, needed as an integral aspect of digitalization efforts. This article discusses the key role of centralized data analytics to fully benefit from the advantages of LEMs in terms of system's security enhancement and energy costs' reduction. Data-driven paradigms are investigated that allow for flexibility from decentralized markets, mitigate the physical security risks, and devise defensive strategies shielding the system from cyber threats.

Synchronization of Packet Coupled Low-Accuracy RC Oscillator Clocks for Wireless Networks

Time-sensitive wireless applications have strict requirements on real-time data transmission and control operation. Even though time synchronisation has been extensively studied for providing a common timing among distributed wireless nodes, there still exists a lack of research for low-accuracy and large-drifting clocks, such as internal Resistor-Capacitor (RC) oscillator clocks with around 4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> parts per million (ppm), which are widely used in wearable sensor systems. This paper proposes a Proportional Packet-Coupled Oscillators (P-PkCOs) protocol for synchronising poor-performing internal RC oscillator clocks with high disturbances in the single-cluster wireless network. The behaviour of such a drifting clock is described as a non-identical and time-varying model. To achieve time synchronisation on low-accuracy internal RC oscillator clocks, a packet-coupled synchronisation scheme is proposed for adjusting drifting clocks via the proportional control-based correction scheme. The RC oscillator frequency in an embedded system cannot be corrected, and this work utilises the clock threshold adjustment as a substitute for frequency correction. The stability region of controller parameters is given to guarantee that the clock threshold approaches a value, which is jointly determined by the nominal threshold and the corresponding clock frequency. We also propose a linear matrix inequality condition to prove that the P-PkCOs performance is robust against the large clock disturbances. We demonstrate the implementation of P-PkCOs. The experimental results show that P-PkCOs can achieve and maintain robust time synchronisation on the internal RC oscillator clocks.

One Network for Europe – Scalability and Replicability in View of Harmonised Electricity Markets

Renewable energy production is mentioned by many as one of the key factors in mitigating the effects of climate change. However, there may be several downsides to the spread of renewables, such as their impact on the balance of the electricity system and on receiving networks. The project OneNet (One Network for Europe) is funded through the EU’s eighth Framework Programme Horizon 2020. It is titled “TSO – DSO (TransmissionDistribution System Operator) Consumer: Large-scale demonstrations of innovative grid services through demand response, storage and small-scale (Renewable Energy Source) generation” and responds to the call “Building a low-carbon, climate resilient future”. While the electrical grid is moving from being a fully centralized to a highly decentralized system, grid operators must adapt to this changing environment and adjust their current business model to accommodate faster reactions and adaptive flexibility. This is an unprecedented challenge requiring an unprecedented solution. Thus, the two major associations of grid operators in Europe, the European Network of Transmission System Operators for Electricity (ENTSO-E) and European Distribution System Operators (EDSO), have activated their members to establish a unique consortium.