Power System Security Research Articles

Operation state classification of power system using fuzzy logic techniques

The occurrence of contingencies in the power system may cause deviation from its ideal operating condition, which initiates the security assessment for efficient operation of the power system. This paper has two objectives. First, to identify and classify the power system states that provides a consistent security analysis. Second, to evaluate each curative action based on the degree of the violation of security constraint for an effective and secure power system. Therefore, a new methodology for operation state classification using the fuzzy logic technique is proposed to achieve these objectives. Moreover, two fuzzy logic controllers are developed. The first one (FLC 1) classifies the operating states of the power system in one of four categories: normal (N), alert (A), emergency (E1) and extreme (E2). The second (FLC 2) specifies the appropriate action to avoid the transition to an extreme state. The simulation program, under MATLAB environment, was applied to evaluate the classification algorithm performances developed using the fuzzy logic technique.

Propagating Uncertainty in Power System Dynamic Simulations Using Polynomial Chaos

Quantifying the uncertainty of the renewable energy generation units and loads is critical to ensure the dynamic security of next-generation power systems. To achieve that goal, the time-consuming Monte Carlo simulations are usually used, which is not suitable for online dynamic analysis of large-scale power systems. To circumvent this difficulty, two uncertainty quantification approaches using polynomial-chaos-based methods are proposed and investigated. The first approach is the generalized polynomial chaos method that is able to reduce the computing time by three orders of magnitude compared with Monte Carlo methods while achieving the same accuracy. We find that this approach is very useful for short-term power system dynamic simulations, but it may produce unreliable results for long-term simulations. To address the weakness of that approach, we present the second method, namely the multi-element generalized-polynomial-chaos method. It is seen that this method is more accurate and more numerically stable than the generalized polynomial chaos method. Since the uncertainties of the renewable energy generation units and loads can follow very different distributions, we extend the Stieltjes’ recursive procedure that allows us to derive the orthogonal basis functions for any assumed probability distribution of the input random variables. Extensive simulations carried out on the WECC 3-machine 9-bus system and the New England 10-machine 39-bus system reveal that our proposed approaches are able to produce comparable accuracy as the Monte Carlo based method while achieving significantly improved computational efficiency for both stable and unstable power system operating conditions.

Research on Optimal Operation of Active Distribution Network with Energy Storage Facilities

With a large amount of intermittent distributed generation(DG) integrating into active distribution network(ADN), the flexibility requirements during the operation process should be paid more attention. Therefore, a dynamic optimal operation model is built. In this model, the maximization of economic benefits during the production cycle is set as the optimization objective, and the constrains of security and flexibility are considered. Then based on this model, the security, economy and flexibility requirements of power system are satisfied by coordination and interaction of different flexible sources. Finally, a case study is given to illustrate the validity and effectiveness of the models.

A Joint Filter Approach for Reliable Power System State Estimation

Accurate power system state estimation facilitates power system control, optimization, and security analysis. In this paper, a joint filter approach is proposed to estimate both the static states (voltage magnitude and phase angle of bus) and the dynamic states (rotor angle, rotor speed, and transient voltages of generator) utilizing the measurements of phasor measurement unit. First, due to the complexity and dynamics of power system, the power system model is usually not known accurately. The uncertainties include both model uncertainty and noise statistics uncertainty. Therefore, $H_\infty $ filter is applied to reliable estimation of the static states. As a link between the static state estimation and the dynamic state estimation, the estimated static states are fed to dynamic state estimation. Next, to deal with the nonlinearity of synchronous generator model, an extended Kalman particle filter is employed to accurately estimate the dynamic states. The numerical tests on IEEE 30-bus system show that the proposed method is into both the static state estimation and the dynamic state estimation.

Convexity of Solvability Set of Power Distribution Networks

The solvability set of a power network - the set of all power injection vectors for which the corresponding Power Flow equations admit a solution - is central to power systems stability and security, as well as to the tightness of Optimal Power Flow relaxations. Whenever the solvability set is convex, this allows for substantial simplifications of various optimization and risk assessment algorithms. In this paper we focus on the solvability set of power distribution networks and prove convexity of the full solvability set (real and reactive powers) for tree homogeneous networks with the same r/x ratio for all elements. We also show this result can not be improved: once the network is not homogeneous, the convexity is immediately lost. It is nevertheless the case that if the network is almost homogeneous, a substantial practically-important part of the solvability set is still convex. Finally, we prove convexity of real solvability set (only real powers) for any tree network as well as for purely resistive networks with arbitrary topology.

A Decision-Making Method for the Loop Closing Operation in 10kV Distribution Network

Loop closing current may affect the security of power system during loop closing operation. In this study, practical criterion of secure loop closing operation is derived by analysing the relationship between current protection and loop closing current. On the basis of the practical criterion, a decision-making method for loop closing operation in 10kV distribution network considering the probability distribution of electric load is proposed. Based on probabilistic load flow theory, the cumulative distribution characteristic of loop closing current can be obtained by cumulant method. Finally, make a decision on loop closing operation according to the over-limit probability of loop closing current. In addition, a method for calculating cumulants of input variables based on historical load data is proposed, which overcomes the shortcomings of traditional numerical methods. The simulation results of a practical study case verify the effectiveness and practicability of the proposed method.

Application of the Source Encryption Algorithm Model in the Power Industry

Abstract With the development of Internet technology and Internet of Things technology, the Internet of Everything has become a hot topic, and in March 2019, the National Grid for the first time clarified the definition of the Pan-In Power Internet of Things, pointing out that the company’s most urgent and important task is to accelerate the construction of the Pan-In Power Internet of Things. The security of Data Transfer on-line at any time is particularly important, in order to ensure the security of data, in the process of data transmission, data needs to be encrypted. This paper expounds a model of the information source data encryption algorithm, analyzes the encryption algorithm and the encryption method, and then provides a reference basis for the data transmission data security of power system.

An advanced platform for power system security assessment accounting for forecast uncertainties

Accounting for the increasing uncertainties related to forecast of renewables is becoming an essential requirement while assessing the security of future power system scenarios. Project iTesla in the Seventh Framework Program (FP7) of the European Union (EU) tackles these needs and reaches several major objectives, including the development of a security platform architecture. In particular, the platform implements a stochastic dependence model to simulate a reasonable cloud of plausible 'future' states - due to renewable forecast - around the expected state, and evaluates the security on relevant states after sampling the cloud of uncertainty. The paper focuses on the proposed model for the uncertainty and its exploitation in power system security assessment process and it reports the relevant validation results.

Estimation of the resonance between forcing and weakly stable oscillations in power systems

Using a simple test example, this paper demonstrates that a weakly damped eigen-oscillation of an electric power system can lead to a loss of stability in the presence of its resonance with forcing oscillation. Such resonant interactions can risk the power system security, as confirmed by recent events in the Western American and Nordic power systems. Conventional eigenvalue analysis cannot detect the observed instability due to its non-linear nature. We show that the critical condition for the appearance of this type of instability can be the value of the perturbation energy accumulated in the system over time. To quantify the risk of stability loss, we examine the model of forcing oscillations and the resonance response of power system in a linear approximation and compare it with the simulation results for the two-area Kundur test system.

An advanced platform for power system security assessment accounting for forecast uncertainties

Accounting for the increasing uncertainties related to forecast of renewables is becoming an essential requirement while assessing the security of future power system scenarios. Project iTesla in the Seventh Framework Program (FP7) of the European Union (EU) tackles these needs and reaches several major objectives, including the development of a security platform architecture. In particular, the platform implements a stochastic dependence model to simulate a reasonable cloud of plausible 'future' states - due to renewable forecast - around the expected state, and evaluates the security on relevant states after sampling the cloud of uncertainty. The paper focuses on the proposed model for the uncertainty and its exploitation in power system security assessment process and it reports the relevant validation results.

Research on Discharging Current Distribution of Grounding Electrodes

Grounding electrodes with good current discharging performance can ensure the reliability of power system security. Discharging current is not only the reason for accelerating the corrosion, but also the key indicator of the grounding electrodes' grounding performance, which directly affects the grounding resistance, step voltage, ground potential distribution, and other macro grounding parameters. This paper focuses on the discharging current distribution of horizontal and vertical grounding electrodes. Based on the FEM of space tetrahedron and space coordinate transformation method, the calculation model of the horizontal grounding with ground lead and the vertical grounding is proposed, and distribution of discharging current on grounding electrodes with different length is analyzed. Results reveal that discharging current distribution on different location of the aforementioned grounding electrodes. Components of discharging current density on grounding electrodes surface and ground lead exhibit sinusoidal distribution along the circumference of the section on grounding electrodes, and discharging current inside the section are more concentrated on the surface of the section and less on the center. Most discharging current near the junction between horizontal grounding electrodes and ground lead is perpendicular to plane defined by grounding electrodes and ground lead.

Impact of wind turbines reliability models on the power generation system reliability

In this paper we describe the methodology of determining the reliability indices for power generating subsystem. We analyse then influence of the considered wind power plant reliability modelling on system reliability. The proposed reliability model of wind power plant is two-state model as compromise between calculation time and accuracy. We have found an empirical relationship between the power system reliability index LOLE (Loss of Load Expectation) and reserve capacity margin for a given wind share. This allowed us to estimate the required minimal reserve capacity margin for a given level of power system security and for a known structure of system installed capacity.

Modeling Fault Propagation Paths in Power Systems: A New Framework Based on Event SNP Systems With Neurotransmitter Concentration

To reveal fault propagation paths is one of the most critical studies for the analysis of power system security; however, it is rather difficult. This paper proposes a new framework for the fault propagation path modeling method of power systems based on membrane computing. We first model the fault propagation paths by proposing the event spiking neural P systems (Ev-SNP systems) with neurotransmitter concentration, which can intuitively reveal the fault propagation path due to the ability of its graphics models and parallel knowledge reasoning. The neurotransmitter concentration is used to represent the probability and gravity degree of fault propagation among synapses. Then, to reduce the dimension of the Ev-SNP system and make them suitable for large-scale power systems, we propose a model reduction method for the Ev-SNP system and devise its simplified model by constructing single-input and single-output neurons, called reduction-SNP system (RSNP system). Moreover, we apply the RSNP system to the IEEE 14- and 118-bus systems to study their fault propagation paths. The proposed approach first extends the SNP systems to a large-scaled application in critical infrastructures from a single element to a system-wise investigation as well as from the post-ante fault diagnosis to a new ex-ante fault propagation path prediction, and the simulation results show a new success and promising approach to the engineering domain.

Integrating Wildfires Propagation Prediction Into Early Warning of Electrical Transmission Line Outages

Wildfires could pose a significant danger to electrical transmission lines and cause considerable losses to the power grids and residents nearby. Previous studies of preventing wildfire damages to electrical transmission lines mostly analyze wildfire and power system security independently due to their differences in disciplines and cannot satisfy the requirement of the power grid for active and timely responses. In this paper, we have designed an integrated wildfire early warning system framework for power grids, taking prediction of wildfires and early warning of line outage probability together. First, the proposed model simulates the spatiotemporal process of wildfires via a geography cellular automata model and predicts when and where wildfires initially get into the security buffer of an electrical transmission line. It is developed in the context of electrical transmission line operating with various situations of topography, vegetation, wind and, especially, multiple ignition points. Second, we have proposed a line outage model (LOM), based on wildfire prediction and breakdown mechanisms of the air gap, to predict the breakdown probability varying with time and the most vulnerable poles at the holistic line scale. Finally, to illustrate the validation and rationality of our proposed system, a case study for a 500-kV transmission line near Miyi county, China, is presented, and the results under various wildfire situations are studied and compared. By integrating wildfire prediction into the LOM and alarming the holistic line breakdown probability along time, this paper makes a significant contribution in the early warning system to prevent transmission lines to be damaged by wildfires, illustrating the related breakdown mechanisms at the line operation level rather than laboratory experiments only. Meanwhile, the implementation of cellular automata model under comprehensive environmental conditions and simulation of the breakdown probability for the 500-kV transmission line could serve as references for other studies in the community.

Transient Stability Analysis of 3-Machine, 7-Bus System Using ETAP

Nowadays, electrical power systems are advancing through continuing development in interconnection, practically through the use of new technology and controls. Therefore, the study of power system stability has been known as an important and challenging problem for secure power system operation. Generally, power system stability is classified into steady state, transient and dynamic stability. The analysis of transient stability is one of the important items in the planning and maintaining for security power system operation. The transient stability is defined as the ability of the power system to keep up synchronism when subjected to a severe disturbance. In this paper, the transient stability analysis of 3-machine, 7-bus system has been performed on electrical transient analyzer program (ETAP) and investigated the determination of whether or not synchronism is maintained when occurred a three phase fault on a transmission line. In addition, this paper described the improvement of the transient stability performance by using power system stabilizer (PSS), it was built-in with a specific generator. This PSS is accomplished by exciter control to provide better response to the system modes of oscillations.

Ant lion optimizer versus particle swarm and artificial immune system for economical and eco‐friendly power system operation

Economic load dispatch (ELD) became recently a mandatory tool for reliable and economic power system operation. ELD improves the security of the power supply while minimizing the generation costs. Daily load curve imposes conflicting requirements on ELD scheme, such as fulfilling demand during peak periods while limiting the cost. Demand response (DR) is an intelligent approach that ensures load demand fulfillment without introducing additional costs. DR allows shifting the electricity consumption to the non-peak periods. Therefore, DR could be considered as a virtual power plant. ELD is usually solved as nonlinear constraint optimization problem. Three simple, fertile, and robust meta-heuristic optimizations are competing in this article for solving ELD incorporating DR as virtual power plant. These are ant lion optimizer (ALO), particle swarm optimization (PSO), and artificial immune system (AIS). The objectives are minimizing the overall cost, system losses, and emission levels. Variety of distinctive study systems are considered to test the functionality and feasibility of the proposed algorithms; they are 6-bus, 30-bus, and 118-bus IEEE systems. MATLAB environment is used for coding ALO, PSO, AIS, and the systems under concern. The comprehensive results show that incorporating DR in ELD reduces the costs/losses/emissions without affecting the power system security and reliability. The comparative results verify the robustness and reliability of ALO in minimizing the overall operating cost and emission levels of the power systems under concern while confining with the constraints. Moreover, they show that ALO has the highest accuracy and convergence efficiency while enjoying the reduced computation storage and execution time.

Power system security enhancement by HVDC links using a closed-loop emergency control

In recent years, guaranteeing that large-scale interconnected systems operate safely, stably and economically has become a major and emergency issue. A number of high profile blackouts caused by cascading outages have focused attention on this issue. Embedded HVDC (High Voltage Direct Current) links within a larger AC power system are known to act as a “firewall” against cascading disturbances and therefore, can effectively contribute in preventing blackouts. A good example is the 2003 blackout in USA and Canada, where the Québec grid was not affected due to its HVDC interconnection. In the literature, many works have studied the impact of HVDC on the power system stability, but very few examples exist in the area of its impact on the system security. This paper presents a control strategy for HVDC systems to increase their contribution to system security. A real-time closed-loop control scheme is used to modulate the DC power of HVDC links to alleviate AC system overloads and improve system security. Simulations carried out on a simplified model of the Hydro-Québec network show that the proposed method works well and can greatly improve system security during emergency situations.

Smoothing ramp events in wind farm based on dynamic programming in energy internet

The concept of energy internet has been gradually accepted, which can optimize the consumption of fossil energy and renewable energy resources. When wind power is integrated into the main grid, ramp events caused by stochastic wind power fluctuation may threaten the security of power systems. This paper proposes a dynamic programming method in smoothing ramp events. First, the energy internet model of wind power, pumped storage power station, and gas power station is established. Then, the optimization problem in the energy internet is transformed into a multi-stage dynamic programming problem, and the dynamic programming method proposed is applied to solve the optimization problem. Finally, the evaluation functions are introduced to evaluate pollutant emissions. The results show that the dynamic programming method proposed is effective for smoothing wind power and reducing ramp events in energy internet.

A Mixed-Integer Linear Programming Approach to Security-Constrained Co-Optimization Expansion Planning of Natural Gas and Electricity Transmission Systems

As the rapid development of natural-gas fired units (NGUs), power systems begin to rely more on a natural gas system to supply the primary fuel. On the other hand, natural gas system contingency might cause the nonavailability of NGUs and inevitably jeopardize power system security. To address this issue, this paper studies security-constrained joint expansion planning problems for this combined energy system. We develop a computationally efficient mixed-integer linear programming (MILP) approach that simultaneously considers N-1 contingency in both natural gas system and electricity power system. To reduce the combinatorial search space of MILP models, an extension of a reduced disjunctive model is proposed to decrease the numbers of binary and continuous variables as well as constraints. The involving nonlinear terms in N-1 constraints are exactly linearized without sacrificing any optimality. Numerical results on two typical integrated energy systems demonstrate the necessity of extending N-1 criterion to the whole network of a combined energy system. Experimental results also show that compared with the conventional approach, our proposed MILP approach achieves a great computational performance improvement in solving security-constrained co-optimization expansion planning problems.

A review of fault ride through of PV and wind renewable energies in grid codes

This paper presents a comprehensive review of fault ride through (FRT) in the grid code of 38 selected countries with an emphasis on renewable energy (REN) sources–related rules. Grid codes are the rules legislated usually by the transmission system operators (TSOs) to determine the grid integration requirements of electrical power generators. Each country establishes its grid code for satisfying the minimum required technical criteria and revises it frequently to cope with new modifications of the utility. Growing the penetration of REN sources have influenced many operational aspects of the power system such as protection, power quality, reliability, and stability. Thereupon, regulations must ensure the power system's secure and controllable operation of REN sources. FRT is one of the main parts of the grid code, and its characteristics affect the performance and rating of power system apparatus. FRT defines the performance of electric power generators during and in postfault conditions. FRT of solar photovoltaic (PV) and wind turbines (WTs) as the main REN sources of energy has great importance in the grid codes. In this paper, a comparison of FRTs in the grid code of 38 countries, including low-voltage ride through (LVRT), zero-voltage ride through (ZVRT), and high-voltage ride through (HVRT) are provided and surveyed.