High Voltage Transmission Network Research Articles

A Risk Assessment Framework for the Socioeconomic Impacts of Electricity Transmission Infrastructure Failure Due to Space Weather: An Application to the United Kingdom.

Space weather phenomena have been studied in detail in the peer‐reviewed scientific literature. However, there has arguably been scant analysis of the potential socioeconomic impacts of space weather, despite a growing gray literature from different national studies, of varying degrees of methodological rigor. In this analysis, we therefore provide a general framework for assessing the potential socioeconomic impacts of critical infrastructure failure resulting from geomagnetic disturbances, applying it to the British high‐voltage electricity transmission network. Socioeconomic analysis of this threat has hitherto failed to address the general geophysical risk, asset vulnerability, and the network structure of critical infrastructure systems. We overcome this by using a three‐part method that includes (i) estimating the probability of intense magnetospheric substorms, (ii) exploring the vulnerability of electricity transmission assets to geomagnetically induced currents, and (iii) testing the socioeconomic impacts under different levels of space weather forecasting. This has required a multidisciplinary approach, providing a step toward the standardization of space weather risk assessment. We find that for a Carrington‐sized 1‐in‐100‐year event with no space weather forecasting capability, the gross domestic product loss to the United Kingdom could be as high as £15.9 billion, with this figure dropping to £2.9 billion based on current forecasting capability. However, with existing satellites nearing the end of their life, current forecasting capability will decrease in coming years. Therefore, if no further investment takes place, critical infrastructure will become more vulnerable to space weather. Additional investment could provide enhanced forecasting, reducing the economic loss for a Carrington‐sized 1‐in‐100‐year event to £0.9 billion.

Nodal vulnerability to targeted attacks in power grids

Due to the open data policies, nowadays, some countries have their power grid data available online. This may bring a new concern to the power grid operators in terms of malicious threats. In this paper, we assess the vulnerability of power grids to targeted attacks based on network science. By employing two graph models for power grids as simple and weighted graphs, we first calculate the centrality metrics of each node in a power grid. Subsequently, we formulate different node-attack strategies based on those centrality metrics, and empirically analyse the impact of targeted attacks on the structural and the operational performance of power grids. We demonstrate our methodology in the high-voltage transmission networks of 5 European countries and in commonly used IEEE test power grids.

Community detection in national-scale high voltage transmission networks using genetic algorithms

The large-scale interconnection of electricity networks has been one of the most important investments made by electric companies, and this trend is expected to continue in the future. One of the research topics in this field is the application of graph-based analysis to identify the characteristics of power grids. In particular, the application of community detection techniques allows for the identification of network elements that share valuable properties by partitioning a network into some loosely coupled sub-networks (communities) of similar scale, such that nodes within a community are densely linked, while connections between different communities are sparser. This paper proposes the use of competitive genetic algorithms to rapidly detect any number of community structures in complex grid networks. Results obtained in several national- scale high voltage transmission networks, including Italy, Germany, France, the Iberian peninsula (Spain and Portugal), Texas (US), and the IEEE 118 bus test case that represents a portion of the American Electric Power System (in the Midwestern US), show the good performance of genetic algorithms to detect communities in power grids. In addition to the topological analysis of power grids, the implications of these results from an engineering point of view are discussed, as well as how they could be used to analyze the vulnerability risk of power grids to avoid large-scale cascade failures.

Influence of Different Coupling Modes on the Robustness of Smart Grid under Targeted Attack.

Many previous works only focused on the cascading failure of global coupling of one-to-one structures in interdependent networks, but the local coupling of dual coupling structures has rarely been studied due to its complex structure. This will result in a serious consequence that many conclusions of the one-to-one structure may be incorrect in the dual coupling network and do not apply to the smart grid. Therefore, it is very necessary to subdivide the dual coupling link into a top-down coupling link and a bottom-up coupling link in order to study their influence on network robustness by combining with different coupling modes. Additionally, the power flow of the power grid can cause the load of a failed node to be allocated to its neighboring nodes and trigger a new round of load distribution when the load of these nodes exceeds their capacity. This means that the robustness of smart grids may be affected by four factors, i.e., load redistribution, local coupling, dual coupling link and coupling mode; however, the research on the influence of those factors on the network robustness is missing. In this paper, firstly, we construct the smart grid as a two-layer network with a dual coupling link and divide the power grid and communication network into many subnets based on the geographical location of their nodes. Secondly, we define node importance () as an evaluation index to access the impact of nodes on the cyber or physical network and propose three types of coupling modes based on of nodes in the cyber and physical subnets, i.e., Assortative Coupling in Subnets (ACIS), Disassortative Coupling in Subnets (DCIS), and Random Coupling in Subnets (RCIS). Thirdly, a cascading failure model is proposed for studying the effect of local coupling of dual coupling link in combination with ACIS, DCIS, and RCIS on the robustness of the smart grid against a targeted attack, and the survival rate of functional nodes is used to assess the robustness of the smart grid. Finally, we use the IEEE 118-Bus System and the Italian High-Voltage Electrical Transmission Network to verify our model and obtain the same conclusions: (I) DCIS applied to the top-down coupling link is better able to enhance the robustness of the smart grid against a targeted attack than RCIS or ACIS, (II) ACIS applied to a bottom-up coupling link is better able to enhance the robustness of the smart grid against a targeted attack than RCIS or DCIS, and (III) the robustness of the smart grid can be improved by increasing the tolerance . This paper provides some guidelines for slowing down the speed of the cascading failures in the design of architecture and optimization of interdependent networks, such as a top-down link with DCIS, a bottom-up link with ACIS, and an increased tolerance .

A New Wind Turbine Generating System Model for Balanced and Unbalanced Distribution Systems Load Flow Analysis

Wind turbine generating systems (WTGSs), which are conventionally connected to high voltage transmission networks, have frequently been employed as distributed generation units in today’s distribution networks. In practice, the distribution networks always have unbalanced bus voltages and line currents due to uneven distribution of single or double phase loads over three phases and asymmetry of the lines, etc. Accordingly, in this study, for the load flow analysis of the distribution networks, Conventional Fixed speed Induction Generator (CFIG) based WTGS, one of the most widely used WTGS types, is modelled under unbalanced voltage conditions. The Developed model has active and reactive power expressions in terms of induction machine impedance parameters, terminal voltages and input power. The validity of the Developed model is confirmed with the experimental results obtained in a test system. The results of the slip calculation based phase-domain model (SCP Model), which was previously proposed in the literature for CFIG based WTGSs under unbalanced voltages, are also given for the comparison. Finally, the Developed model and the SCP model are implemented in the load flow analysis of the IEEE 34 bus test system with the CFIG based WTGSs and unbalanced loads. Thus, it is clearly pointed out that the results of the load flow analysis implemented with both models are very close to each other, and the Developed model is computationally more efficient than the SCP model.

Error reduction of phasor measurement unit data considering practical constraints

Wide area measurement system relies on phasor measurement unit (PMU) data to monitor, protect, and control high-voltage transmission networks. However, errors in instrument transformers (ITs) located at the inputs of a PMU can significantly degrade its output quality. This study proposes two methodologies for voltage and current transformers calibration using PMU data. The first method calibrates ITs using one good quality voltage measurement located at a tie-line. This method tolerates errors in both the ITs (which are to be estimated) as well as the PMUs. The second method attains the same objective as the first one, with the additional constraint that some portion of the data is unusable. Thus, the second method can be used even when the incoming data is intermittent.

Vulnerability Assessment of a Large Electrical Grid by New Graph Theory Approach

In previous research a novel methodology to assess structural vulnerability was proposed and applied in IEEE test system and high voltage transmission networks of 94 buses, by using graph theory to investigate various risk scenarios that can trigger cascading failures. In this paper we validate the application of this methodology in larger networks by applying a case study on the transmission network 230 and 400 kV of Mexico. The events of cascading failures are simulated through two elimination strategies: by deliberate attacks on critical nodes or by random errors. Iterations are performed by running successive N-1 contingencies on a network that is constantly changing its structure with the elimination of each node. The power flows are not necessary and only the calculation of the graph statistical parameter “geodesic vulnerability” is required. This reduces the computation time and leads to a comparative analysis of structural vulnerability.

Cascading Failure Analysis of Cyber Physical Power System With Multiple Interdependency and Control Threshold

The traditional infrastructure in power system is undergoing a transition to the Smart Grid, in which the communication network and power grid will be integrated into a cyber-physical power system (CPPS). Although the traditional topological analysis reveals the mechanism of cascading failure between two networks, it ignores the control redundancy and standby lines from communication network to power grid. The robustness analysis in CPPS requires a more comprehensive model to analyze failure behavior in reality. Here, we propose a cascading failure model with one-to-multiple interdependency and a relevant theoretical framework to analyze CPPS cascading failure. In consideration of real CPPS, in the proposed model we introduce two robustness factors, the number of dependent links and control threshold, which can better describe the control function from communication nodes to power nodes. The remaining fraction under different initial attacking on high voltage transmission network, small world network, double star network, and the different topological combination of CPPS are analyzed. The results show that the proposed model and robustness factors can better reveal the robustness and the mechanism of two networks in cascading failure.

Clarifying the Applicability of the Private Investor Test ∙ Case T-747/15 EDF v Commission ∙ Annotation by José Antonio Rodríguez Miguez

This is an interesting judgement on the applicability of the Market Economy Investor Principle (MEIP). It confirms a second Decision which the EC adopted in 2015 once that its first Decision on the same case was annulled by the GC in a previous judgement, later confirmed by the ECJ in 2012. The main reason of the initial annulment was that the fiscal form of a measure did not exclude the possibility of applying the MEIP to it. France considered that, under the form of a tax exemption, the measure was materially a recapitalization and the EC had simply to look at whether it was materially in line with MEIP or not. The new judgement, however, considers that the EC had still to examine first whether the MEIP was ‘applicable’ at all to this tax exemption (since this, according to the GC, was not decided in the previous judgements). For the GC the ‘applicability’ of MEIP depended on whether France treated at the time that measure as an ‘investment’ by adopting an ex ante evaluation and business plan. The burden of proving this was for the Member State but the EC had to examine the evidence brought to the procedure. Since the GC considered that this was not proved here, there was no legal need to examine whether the MEIP was materially fulfilled or not. Keywords: State aid; Aid granted by the French authorities to EDF; Reclassification, as a capital contribution, of accounting provisions created free of tax for the renewal of the high-voltage transmission network; Decision declaring the aid to be incompatible with the internal market; Authority of res judicata; Private investor test.

Effective Elimination Factors to the Generated Lightning Flashover in High Voltage Transmission Network

Effective Elimination Factors to the Generated Lightning Flashover in High Voltage Transmission Network

A Less-Effort Method for Spatial Network Planning

This paper presents a method to solve spatial network planning (SNP) in power systems expansion. SNP is an integration of transmission expansion planning (TEP) and optimal line routing problems. In fact, SNP considers the impacts of lines routing on the network power flow. Therefore, it can exploit such impactsto attain a signi cant techno-economic solution. In this work, a preprocess stage is employed to reduce the computational e ort demanded by line routing. Furthermore, a meta-heuristic algorithm is engaged to solve such a complicated problem. Applying these modi cations made it possible to solve SNP for large-scale systems with high-resolution rasterized maps. The proposed method is applied to a 3-bus system, an 18-bus test system as well as the original and modi ed versions of the IRAN southeast high-voltage transmission network to demonstrate the capability of the proposed methodology.

Noniterative Parameter-Free Fault Location on Untransposed Single-Circuit Transmission Lines

Extra high voltage transmission networks include many untransposed single-circuit overhead lines with horizontal configuration of phase conductors. This paper develops a setting-free fault-location method specific to these types of transmission lines. Utilizing synchronized measurements at line terminals, the proposed method accurately locates faults irrespective of fault type, fault resistance, external network parameters, and faulted-line parameters. As such, fault location is robust against ambient conditions as well as inherent inaccuracy of line parameters. The bisymmetry of the impedance matrix of the line is utilized to obtain a closed-form solution for fault location on short transmission lines. For long transmission lines, shunt capacitance of the line is taken into account to obtain an accurate closed-form estimation for fault location. Electromagnetic transient simulation in PSCAD/EMTDC environment validates the accuracy of the proposed fault-location method for a long untransposed 400-kV transmission line. The obtained results are also compared with an existing noniterative parameter-free fault-location method to demonstrate salient features of the proposed method.

An Integrated Control Strategy With Fault Detection and Tolerant Control Capability Based on Capacitor Voltage Estimation for Modular Multilevel Converters

Modular multilevel converters (MMCs) will be extensively used in the high-voltage direct-current transmission networks because of its superior characteristics over line commutated converter. Increasing the reliability of the MMC is directly related to the balancing of the MMC submodule capacitors voltages, which guarantees the proper operation of the converter and lowers the stress on the submodules. This paper presents an adaptive voltage-balancing strategy based on the capacitor voltage estimation, utilizing a hybrid adaptive linear neuron recursive least squares scheme. The proposed strategy eliminates the need of measuring submodules capacitor voltages and associated communication link with the central controller. Furthermore, the estimated capacitor voltages are utilized to detect and localize different types of submodule faults. After isolating the faulty submodules, the proposed fault-tolerant control unit modifies the parameters of the voltage-balancing strategy to overcome the reduction of the active submodules. The dynamic performance of the proposed strategy is investigated, using PSCAD/EMTDC simulations and hardware-in-the-loop real-time simulations, under different normal and faulty operating conditions. The accuracy and the time response of the proposed fault detection and tolerant control units result in stabilizing the operation of the MMC under different types of faults. Consequently, the proposed integrated control strategy improves the reliability of the MMC.

Topological and Statistical Analysis for the High-Voltage Transmission Networks in the Korean Power Grid

Topological and Statistical Analysis for the High-Voltage Transmission Networks in the Korean Power Grid

Streamer parameters and breakdown in CO2

CO2 is a promising gas for the replacement of SF6 in high-voltage transmission and distribution networks due to its lower environmental impact. The insulation properties of CO2 are, therefore, of great interest. For this, the properties of streamers are important, since they determine the initial discharge propagation and possibly the transition to a leader. The present experimental investigation addresses the streamer inception and propagation at ambient temperature in the pressure range 0.05–0.5 MPa at both polarities. Streamer parameters, namely the stability field, radius and velocity, were deduced in uniform and in strongly non-uniform background fields. The measured breakdown fields can then be understood by streamer propagation and streamer-to-leader transition.

EDF, A Leading Case Revisited: The Application of the Market Economy Operator Test to Fiscal Measures and the Energy Sector.

The European Energy Internal has changed completely the environment of the Energy Sector in Europe. This deep transformation was a consequence, almost in a very significant part, of the regular application of the European Competition Law rules. The evolution of Energy Sector in Europe, where the most important firms were the old monopolists, generally in hands of the public sector, it is based on the expandable delimitation of the notion of Services of General Economic Interest (SGEI) and their missions contained in Article 106.2 TFEU and in the well-known doctrine of the essential facilities.In this new context, both the European Commission and the National Competition Authorities started a strong fight not only against anti-competitive agreements and abuses of dominant position, but also against illegal state aid.In the field of state aid control, many of the Leading Cases on the complex notion of State Aid from Article 107.1 TFEU are many of them related with taxation. The Case is one of these leading cases, and the principal object of this paper.In EDF case, the European Commission analyses, in a second decision, after the General Court and the Court of Justice had annulled the first one, the reclassification as capital of the tax-exempt accounting provisions for the renewal of the high-voltage transmission network (RAG) implemented by France in favour of one of the biggest European firms in the energy sector. This decision gives very interesting remarks on the application of the Market Economy Investor Test, on a measure financed by public resources from a tax instrument.

On Variable Reverse Power Flow-Part II: An Electricity Market Model Considering Wind Station Size and Location

This is the second part of a companion paper on variable reverse power flow (VRPF) in active distribution networks (ADNs) with wind stations (WSs). Here, we propose an electricity market model considering agreements between the operator of a medium-voltage active distribution network (MV-ADN) and the operator of a high-voltage transmission network (HV-TN) under different scenarios. The proposed model takes, simultaneously, active and reactive energy prices into consideration. The results from applying this model on a real MV-ADN reveal many interesting facts. For instance, we demonstrate that the reactive power capability of WSs will be never utilized during days with zero wind power and varying limits on power factors (PFs). In contrast, more than 10% of the costs of active energy losses, 15% of the costs of reactive energy losses, and 100% of the costs of reactive energy imported from the HV-TN, respectively, can be reduced if WSs are operated as capacitor banks with no limits on PFs. It is also found that allocating WSs near possible exporting points at the HV-TN can significantly reduce wind power curtailments if the operator of the HV-TN accepts unlimited amount of reverse energy from the MV-ADN. Furthermore, the relationships between the size of WSs, VRPF and demand level are also uncovered based on active-reactive optimal power flow (A-R-OPF).

Study of System Stability Based on the Combination of Low Voltage Protection and Security Automatic Device

Large disturbance stability of the system was greatly affected by the way of a lot of wind power centralized access to high voltage transmission network. We could use the traditional operation control scheme of controlling the wind farm and the nearby generator system operation output, but the wind farm and conventional power plant's interests would be seriously affected. Therefore, this paper put forward the control strategy by using the combination of low voltage protection and security automatic device. Large disturbance stability level could reach or close to the level before the wind, so as to minimize the impact of wind power integration on large disturbance stability of power system.

A distributed state estimation method for power systems incorporating linear and nonlinear models

Abstract High-voltage transmission networks are commonly equipped with phasor measurement units (PMU), and some of them are PMU observable. However, PMUs are seldom installed in distribution networks due to budget limitations. The state estimation equations of PMU observable areas are linear, while those of other areas remain nonlinear. This paper proposes a new distributed state estimation method for solving multi-area state estimation problems, in which linear models are used for high-voltage transmission network, while nonlinear models are adopted for other areas. In PMU observable area, we select coordinating variables as generalized cost functions which accurately represent the sensitivity between the linear SE objective function and boundary states. Consequently, SE results identical to a centralized estimator can be obtained without iterations at the coordination level. This paper presents the problem model and theoretical analysis of the proposed method, and shows its effectiveness by numerical tests.

English

Instrument transformers are the integral components of power system protection and metering. The objective of instrument transformers is to provide scaled down replicas of high voltages and currents of the power system. In case of high voltage transmission network (≥132KV), capacitive voltage transformers are widely used as an alternative to electromagnetic voltage transformers due to their techno economic advantages. They transform higher voltages to lower values which are easily measurable and can be directly used for metering, protection and control applications. During the system transient conditions, there is a deviation in the scaled down secondary voltage signal from the actual signal which comprises of wide range of frequencies, due to energy storing elements of capacitive voltage transformer. There are several practices in the industry to mitigate the deviation in the secondary voltage signal of capacitive voltage transformer. For satisfactory operation of capacitive voltage transformer, better frequency response is desirable. The simulation study to determine the effect of various factors influencing the frequency response of capacitive voltage transformer are presented in this paper.