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With the integration of large scale wind power, the characteristics of power system operation has been changing, and, some problems come forth. On-line security assessment and control decision support system provides the stability and security state message for dispatcher in time, and, some suggestions to improve the level of power system stability and security. To suit the requirements of large amount wind power integrated power system, the technology of on-line security assessment and control decision support must be modified. This paper focuses on the technology of on-line security assessment and control decision for operation of power system with large scale wind power and designing the support system. In the paper, the study and application of on-line security assessment and control decision support technology in China are introduced. Considering the wind power in China having some distinct characteristics such as large scale, centralized development, long-distance and high voltage transportation, the new requirements to on-line security assessment and control decision support are analyzed. They includes need for new information, on-line modelling with large scale wind farm, transfer limitation calculation under the constraint condition of wind power integration requirement, auxiliary preventive control decision based on the forecasting and adjustment properties of wind power output, coordinated emergency control wind power with hydraulic and thermal power. On the basis of technical rule for connecting wind farm into power grid and the interaction between wind power and power grid, the advices on engineering application of on-line security assessment and control decision support technology for large amount wind power integrated power system, are proposed, for example, with respect to the standard of security assessment and selection of pre-contingency sets. (7 pages)

Wind power generation changes the load flow, the swing modes and transient stability of the integrated power system. The characteristic of power transient stability is well studied for large scale wind power integration in this paper. Different wind power generator models, including fixed speed induction generator (FSIG) and double-fed induction generator (DFIG), are considered in the analysis, as well as different penetration levels, faults locations and faults clearing time. By using extended equal area criterion (EEAC), it was revealed that large scale wind power integration may change the unstable mode (UM), namely the pattern of dividing all generators into the critical cluster (CC) and the remaining one (RC), the times of the swing for an unstable case, or the change rate of the swing stability margin for a stable case. If some traditional synchronous generators within the CC are replaced with wind power generators, power system transient stability degree can be either decreased or increased. Similarly, these phenomena might also appear if the replacement occurs in the RC. Based on EEAC, this paper presents such cases with simulations, and conducts theoretical and quantitative analyses to explain the mechanisms behind. The impacts of large scale wind power on system power transient stability can be mainly ascribed to the change of the equivalent generalized inertia of the CC and that of the RC, and their equivalent accelerating power.

In order to cope with extreme natural disasters which appear more and more frequently, it is necessary to extend the data acquisition range from traditional electric quantity of power systems to macroscopic and microcosmic meteorology data, such as those on thunderstorm, typhoon, ice and snow, as well as pollution flashover, etc. Due to the mechanisms' differences, the data needed for early-warning might be different for various types of natural disasters. Taking thunderstorm as an example, this paper analyzes the mechanisms of natural disasters affecting power systems. The required data are discussed and an early-warning method is proposed based on data provided by a lighting location system. Firstly according to the proposed criteria, the thunder locations detected within the current interval are grouped into areas; secondly the results are matched with those of the previous interval; finally the most possible thunder areas can be estimated for the next several intervals. Unlike traditional models with annual average probability of thunder-striking faults, the proposed real-time probability model which considers real-time information is space dependent, as well as time dependent. Instead of being fixed, the list of preassigned faults to be on-line assessed is time varying. Thus, the task of online security analysis is adaptive and more efficient.

Pollution of the power plant has caused harmful environmental effects due to the emission of greenhouse gas. The pollution can be reduced by adjusting the real power outputs of different power plants. However, the relocation of real power outputs results an additional outlay in the system. In order to eliminate the conflict between the cost and emission, an optimal power flow is introduced in this paper, which aims to study the trade-off relationship between the economic dispatch and the power plant emission. Simulation results on the IEEE 30-bus power system demonstrates the perspective of solving the environmental-economic power dispatch problem by a novel optimization algorithm.

In market environment, the decisions of generation and network planning are made by separate economic entities, rather than one integrated utility. Because of the physical connection between generation and network, it is necessary to coordinate the two kinds of planning and solve the conflicts between the subjective individual game actions in economic and the objective law in physical. The current researches on the coordination between the two kinds of planning are reviewed and their shortages are indicated. The interactive influence between generation planning and network planning is discussed. Power trading is constrained by network congestions, and the competitive forces of the generators in congested areas are relatively lower. Constructing new lines and other relevant infrastructures can relieve congestions and reduce operation risks. Meanwhile, the competitive forces of the generators are affected differently. The newly-built generating capacity may enlarge the investor's market share and profitability. At the same time, it may influence the grid congestion situation and grid operation risks. The influences of the investors' planning to the economic efficiency of the power industry are also analyzed based on the hybrid simulation. On the basis of a discussion about the regulator's responsibilities in system planning, a preliminary regulation or coordination mechanism is suggested. After all the market entities submit their planning, regulator will issue audit opinions and modify the information on generalized congestions resulting from simulations. All investors can adjust their own decision under the guidance of the new constraints and submit their planning again. The tentative process would be iterated until satisfactory results are achieved. The experiments based on DSPMPS (Dynamic Simulation Platform for Power Market and Power System) analysis the interaction between the two kinds of planning and the influence of the two kinds of planning to the whole system.

Essentials of power system dynamic behavior, the character and difference index of disturbed trajectories are summed up in this paper. The model verification and parameter identification methods based on difference index of disturbed trajectories are reviewed, as well as the existed problems and possible development. The index should not be based on conventional signal processing technologies only; however it should reflect the physical mechanisms of the system dynamics. It is revealed that there exist multi-solution phenomena in multi-parameter identification, thus the identification results depend on both initial value and search strategy. This problem might be solved with applying multiple sets of measured response curves as benchmarks in different scenarios, and the objective parameters should remain unchanged during getting these benchmark curves.

A new probabilistic optimal power flow method is developed to manage electricity market price risk. The proposed method is an adaptive importance sampling method which based on the principle of importance sampling and reinforcement learning. The estimation result of conventional Monte Carlo simulation is taken as benchmark. Case study is conducted on IEEE 39-Bus system to compare the proposed method with point estimate method, which shows the feasibility and efficiency of the method.

Discriminating between the magnetizing inrush and the internal fault of a power transform is a major challenge when designing differential transformer protection. In this paper, a novel method, which is based on mathematical morphology (MM) and artificial neural network (ANN), is proposed to solve this problem. Firstly, an MM based stage is used to extract shape features from differential currents, then after a scaling preprocessing which removes magnitude information, the features is fed into an artificial neural network (ANN) to be identified. Using this method, an effective output, which is used to block a false tripping, can be generated slightly longer than half of a period after the occurrence of an inrush condition. By using extracted features instead of raw samples of currents as inputs of an ANN, less inputs are presented to the ANN, which yields a simpler network structure. The computational load required by this method is greatly lower than those which are only based on an ANN, thus it is suitable to be implemented in resource constrained embedded systems. This method has been implemented by using MATLAB and evaluated on the data obtained from PSCAD/EMTDC simulation. The evaluation tests show promising results.

An accurate model of large scale wind farm is demanded for researches about the impacts on the power grid. The total number of wind energy generators is so large that the detailed model of wind farm is computationally prohibitive. Dynamic equivalence can significantly reduce system order with the major characteristics retained. So the aggregation of large scale wind farm is inevitable. An overview of dynamic equivalent methods has been made for wind farms consisting of the widely used wind generators such as the doubly fed induction generator (DFIG) or the squirrel-cage induction generator (SCIG). The dynamic models of DFIG and SCIG and the mechanisms are briefly introduced at first. The wind energy generator is compared with induction motor to show the differences and similarities. Next, the possibility of the existing dynamic equivalent methods such as coherency-based method, parameter identification method and modal equivalent method to be used in wind farm aggregation is studied. The clustering criterions and model validation of wind farms are investigated. The feature and shortcoming of the re-scaled power capacities method are also discussed. At last, some suggestions are given for future equivalent researches of wind farms.

This paper proposes a new control design scheme for doubly fed induction generator (DFIG) based wind generation systems to damp interarea oscillations of power systems. The control system of DFIG consists of two parts. The first part is the primary power and voltage (PV) control. The second part is a supplementary damping controller (SDC) based on PV control, designed to enhance damping of interarea oscillations. To achieve the best performance, parameters of these two controllers are simultaneously tuned by using a differential evolution (DE) algorithm. Results of simulation on a two-area system incorporating a wind turbine generator demonstrate that the proposed control scheme can effectively suppress the interarea oscillation of the system.

Optimal Power Flow (OPF) is an effective tool for dispatch planning of power systems, and the algorithms aiming to solve the OPF have been widely studied. Among these algorithms, the Evolutionary Algorithms (EAs) are a popular type, which have been investigated. However, EAs are also notorious for the intensive computation caused by a large amount of evaluations of the objective function required by all individuals. In this paper, a stochastic OPF problem is introduced to describe a more realistic power system, which relies on a large number of evaluations. In order to reduce the computational time, a Paired-Bacteria Optimizer (PBO) based on a single bacterium foraging model is adopted to solve this expensive optimization problem. The PBO has been tested on high dimensional multimodal benchmark functions and applied for a stochastic optimal voltage control and fuel cost reduction problem which is a crucial part of power system planning. The experiment results have shown that it has a more reliable performance than the widely applied EAs.

This paper proposes a scheme based on the embedding theorem to locate and classify the transient disturbances in power system signals. The disturbance signals are transformed to the phase space, where the normal part of the signal and the disturbance form two waveforms that can be distinguished from each other, and the location and classification are based on the information obtained from the embedded signal. The scheme has been tested on five different disturbances under different conditions, and simulation results show that it can accurately detect the disturbances and its performance is stable.

Multi-objective optimal controller design of a doubly fed induction generator (DFIG) wind turbine system using Differential Evolution (DE) is presented in this chapter. A detailed mathematical model of DFIG wind turbine with a close loop vector control system is developed. Based on this, objective functions, addressing the steady state stability and dynamic performance at different operating conditions are implemented to optimize the controller parameters of both the rotor and grid side converters. A superior e-constraint method and method of adaptive penalties are applied to handle the multi-objective problem and the constraint with DE. Eigenvalue analysis and simulation are performed on the single machine infinite bus (SMIB) system to demonstrate the control performance of the system with the optimized controller parameters.

The paper introduces the three stages of research and development of distributed generation (DG) in China: 1) stand-alone DG systems; 2)Grid-connected DG systems; 3) A micro-grid with multi-energy Generators (MGMEG). A comprehensive testbed for MGMEG(TB-MGMEG) in lab built in Hefei University of Technology(HFUT), China is described in detail. The TB-MGMEG includs wind, photovoltaic, and fuel cells, energy storage and local loads with maximum power 200kW. Its features are single-phase, three-phase and multi-AC buses with energy management system (EMS) that conforms to the IEC61970 standards.

The Frequency Monitoring Network (FNET) provides a low-cost, easily deployable method for wide-area monitoring. FNET has the capability to realize long term, high density and continuous monitoring of large interconnected power systems. In effect, there are potentials for ground-breaking research on wide-area monitoring and control. In this paper, low frequency oscillations in the Eastern Interconnection (EI) are analyzed based on generation trips detected by FNET in 2007. The oscillation data were selected in a way such that their locations are distributed throughout the EI system. In addition, some preliminary statistical analysis of the dynamic characteristics is presented. Through illustrating the control method of system stability, it is shown that the analysis of oscillation mode shape distribution is very important. As an example, some preliminary simulation results are provided for the control of system low-frequency oscillation due to transmission line faults or other changes in system topology.

This paper presents the development of an agent based bidding model, that closely represents the process each active generator may undertake prior to the bidding and during the rebidding process in an electricity market. The processes that had been modelled include the analysis of historical demand/prices, the forecasting of future spot prices and demand; the formulation of daily bids and the readjustment of bids during the trading process. The uniqueness of this model is the integration of human risk preference under conditions of limited information. This model was tested with data from the Australian National Electricity Market (NEM). (7 pages)

This paper investigates Chinese standards for power system security and the practices in the relevant strategy. Considering the cascading features of typical system-wide blackouts around the world, further emphasis is given to integration of various wide area measurements, trajectory-based knowledge extracting, on-line quantitative security analysis, and adaptive optimization of preventive control, emergency control, corrective control and recovery control, in order to upgrade the three-defense-line to an adaptive space-time cooperative framework. Functions, features and engineering experiences of such a framework in China are reported.

In this paper, key techniques, limits and feasible applications of wide area measurement system (WAMS) and wide area control system (WACS) are investigated and the framework for Wide area Monitoring Analysis Protection-control (WARMAP) is introduced to break those limitations. Based on engineering experiences in China, application functions depending merely on phasor measurement unit (PMU) data are clarified; those using both PMU data and model simulation results are explored. The paper also points out the bottleneck and the possible solutions, and reports engineering applications of WARMAP in power grids in China.

The recently developed Extended Equal Area Criterion (EEAC) method has proved to be an accurate and extremely fast transient stability assessment method for the classical model. This model may be too rough for some practical engineering uses. In this paper, the EEAC method is successfully extended to managing the two-axis generator model, i.e. the constant Eq’ model, which may be accepted by more utilities for both planning and operation purposes. The proposed EEAC(Eq’) method has been extensively tested for hundreds cases with faults at all buses in the GREEK system and a Chinese regional system; and very promising results have been obtained. This generalization of EEAC method preserves its accuracy and extremely fast speed.

There are two compensation methods for interruptible loads (ILs), namely low price compensation before supply unavailability and high price compensation after supply unavailability. Low price compensation is independent of power supply unavailability, while the high compensation is performed only after actual power supply unavailability. However, the IL with low price (ILL) and the IL with high price compensation (ILH) have only been studied separately till now. Based on risk management, this paper analyzes the different economic properties of the two compensation methods and concludes that their coordination is beneficial to restrain market power and reduce the cost of reserve capacity. The authors propose the coordination models and optimization algorithms by taking the sum of the deterministic reduction of revenue resulting from ILL and the risk of compensating ILH as the objective function. Simulation results are presented to validate the effectiveness of the proposed method.

With investigation on recent blackouts around the world, the three-defence-lines criterion, which has been the security standard for power systems in China, is reviewed. An adaptive space-time cooperative framework, named as Wide ARea Monitoring Analysis Protection-control (WARMAP) for defending power system against blackouts is introduced in this paper. It upgrades the individual defence lines to a global scheme. Its essentials are: (1) acquiring wide area measures by using RTUs, PMUs, fault recorders, protection management systems and system protection schemes; (2) integrating all information acquired via various equipments into a unified platform; (3) performing trajectory-based data mining and quantitative security analysis for time response curves obtained by PMUs or simulations; (4) adaptive optimization of preventive control, emergency control, corrective control and recovery control; (5) coordination among these controls; (6) coordinatin among WARMAPs in a multi-layer power system. It is well on the way to building WARMAPs in a two-layer power grid in China, which consists of East China Regional Grid and Jiangsu Province Grid.

Concerned with a 3 phase to ground permanent fault occurred at the two terminal of the 500 kV Luohe-Yingzhou transmission line in the Anhui power grid, the instability mechanism of the Anhui power grid when such a fault occurred is analyzed from the conventional point of view and also with the EEAC theory. The qualitative and quantitative explanations are also given to the cause of the stability difference when the fault occurs at different locations on the concerned line.

This presentation investigates Chinese standards for power system security and the practices in the relevant three-defense-lines. It also proposes an adaptive space-time cooperative framework for defending power system blackouts. Its essentials are: (1) acquisition and integration of wide area measurements from RTUs, PMUs, fault recorders and protection systems; (2) trajectory-based data mining and quantitative security analysis; (3) adaptive optimization of preventive control, emergency control, corrective control and recovery control; (4) coordination among these controls. Recent blackouts around the world are investigated and their mechanisms are revealed. The three-defense-lines criterion, which is the security standard for power system in China, is thoroughly reviewed. It is suggested to advance the existing SCAD A/EMS systems to dynamic ones, namely DSCADA/DEMS. Based on relevant research achievements, such a system, named as Wide ARea Monitoring Analysis Protection-control (WARMAP), is well on the way to building in both East China Power Grid and Jiangsu Power Grid. (1 page)

Ensuring secure operation has always been of paramount importance in the safe and economic operation of power systems. However, the evolution of the electric power industry toward open markets has introduced a number of factors that have heightened the need for more rigorous security assessment and, in many cases, made it much more challenging. Some of these factors include: 1) aging transmission infrastructures/spl rarr/potential component failures; 2) lack of new transmission facilities/spl rarr/bottlenecks; 3) large numbers of small and distributed generators/spl rarr/uncertainty in dispatch patterns; 4) market-driven transactions/spl rarr/unpredictable transactions and system usage; 5) cutbacks in system maintenance/spl rarr/potential for failures such as flashovers to trees; 6) dependence on communications and computer systems/spl rarr/software/hardware failures may leave operators blind; 7) neglect of integrated system planning/spl rarr/insufficient/improper generation/transmission resources; 8) trend toward interconnection/spl rarr/exposure to cascading disturbances. These factors have (a) lead to greater uncertainty in day-today system operations, (b) increased the number of potential sources for system disturbances and (c) increased exposure to phenomena such as voltage instability and inter-area oscillations. As a result, in many power systems, it has become impossible to operate systems with an acceptable degree of security by using traditional operational planning studies that are conducted off-line and use forecast conditions to predict system security limits. This has been illustrated by the major system disturbances that have recently occurred in different systems around the world; highlighting the importance of being able to monitor and ensure system security. Therefore, the use of on-line security assessment is quickly becoming a necessity. This paper presents an overview of the critical components required for on-line security assessment and provides a description of an actual implementation of an on-line security assessment system.

This special section addresses the challenges and opportunities for the development of a transmission grid with applications to smart grid and brings together the most recent advances from concept to implementation in the field of transmission operation, control, and planning worldwide. The special section covers the design and planning of operation and communication systems of smart transmission grids; state estimation of smart transmission grids; smart voltage and power flow control as well as generalized power network management; wind generation and emission constrained despatching for smart grids; smart demand as power grid services; wide area monitoring, control as well as emergency control. A summary is provided for each of the articles and features presented in this special section.

Transient voltage security means that the power system is both transient voltage stable and transient voltage dips acceptable. These definitions are clarified in this paper. A self-start technique for computing transient voltage stability related limits is proposed. Based on a margin for transient voltage dip acceptability, a criterion for early termination of the simulation is put forward. Moreover, the procedure of calculating critical clearing time for transient voltage security is extended to that of calculating the critical load level, the minimum reactive power resources and minimum load shedding for keeping transient voltage security. It is also suggested that transient angle stability and transient voltage stability and transient voltage dip acceptability be quantitatively assessed along the same simulation trajectory. The most critical one among the three kinds of limits is regarded as the global transient security limit. The effectiveness and robustness of the proposed approach are demonstrated in this paper with statistic information resulting from 47,987 test cases on two practical power systems.

Based on the stability margin provided by the EEAC, the unstable contingencies can be classified into sets according to their unstable modes. This two-part paper develops a globally optimal algorithm for transient stability control to coordinate preventive actions and emergency actions. In the first part, an algorithm is proposed for a set of contingencies having identical unstable modes. Instead of iterations between discrete emergency actions and continuous preventive actions, the algorithm straightforwardly searches for a globally optimal solution. The procedure includes assessing a set of insufficient emergency schemes identified by the EEAC; calculating the related preventive actions needed for stabilizing the system; and selecting the scheme with the minimum overall costs. Simulations on a Chinese power system highlight its excellent performance. The positive results obtained are explained by analogizing settlements for 0-1 knapsack problems using the multi-points greedy algorithm.

The Ertan Hydroelectric Power Development Project with a total capacity of 3300 MW and the associated 500 kV power transmission project is the largest of its kind in China before the Three Gorges Power Transmission Project. An on-line pre-decision system (OPS-1) has been built and tested in the laboratory for its emergency control. Based on on-line stability analysis and pre-decision-making, OPS-1 follows the measured operating condition and refreshes the look-up decision table periodically. Therefore, it is adaptive to operating condition change and structure evolution of the power system, and is a fundamental innovation on the present emergency control system. OPS-1 integrates the unique EEAC technique for quantitative analysis of stability, an integer programming for nonconvex nonlinear optimization of transient stability control, an object-oriented distributed processing platform for contingency-oriented parallel computation into distributed devices for emergency control. The control system structure, decision searching algorithm and laboratory test results are presented in this paper.

Generation investment decision-making is a very complicated problem in the electricity market environment because of various kinds of uncertainties. The enforcement of the emissions trading scheme will make the problem even more complicated, especially for coal-fired generation units. Given this background, a new approach is developed for evaluating the value of a generation investment project in the electricity market environment with emission trading enforced. A real option-based model for this purpose is proposed, and the project value and optimal investment timing are obtained by employing the least-square Monte-Carlo method. The impacts of market factors and the regulation policy upon generation investment decision-making are illustrated by numerical examples in different scenarios.

The continuum model is a key paradigm describing the behavior of electromechanical transients in power systems. In the past two decades, much research work has been done on applying the continuum model to analyze the electromechanical wave in power systems. In this work, the uniform and non-uniform continuum models are first briefly described, and some explanations borrowing concepts and tools from other fields are given. Then, the existing approaches of investigating the resulting wave equations are summarized. An application named the zero reflection controller based on the idea of the wave equations is next presented.

The Indian power system underwent two separate massive blackouts on 30th and 31st of July 2012. These blackouts exposed a series of inherent problems underlying the power system of India, such as its generation planning, transmission planning, grid infrastructure, management systems, primary energy resources, environmental constraints, electricity market, and information technology, which together aggravate the massive blackouts. These factors which affect the adequacy and security of the power supply in a similar manner as the transmission congestion of physical grids does, can be called by a generic term as generalized congestion. Competitive manipulations and “game-playing” between various interested parties further intensifies these congestions. Here, from the perspective of generalized congestions, the paper reflects the inevitability of India's massive blackouts, discusses occasional effects of trigger events, inherent evolution law of blackouts and the enlightenment on power industry in China, and explores risk control measures to defend blackouts in China. The positive role of strong smart grid in insuring energy and environment security is highlighted.

In the last two decades, the wind power generation has been rapidly and widely developed in many regions and countries for tackling the problems of environmental pollution and sustainability of energy supply. However, the high share of intermittent and fluctuating wind power production has also increased the burden of system operator for securing power system reliability during the operational phase. Moreover, the power system restructuring and deregulation have not only introduced the competition for reducing cost but also changed the strategy of reliability evaluation and management of power systems. The conventional long-term reliability evaluation techniques have been well developed, which have been more focused on planning and expansion rather than operation of power systems. This paper proposes a new technique for evaluating operational reliabilities of restructured power systems with high wind power penetration. The proposed technique is based on the combination of the reliability network equivalent and time-sequential simulation approaches. The operational reliability network equivalents are developed to represent reliability models of wind farms, conventional generation and reserve provides, fast reserve providers and transmission network in restructured power systems. A contingency management schema for real time operation considering its coupling with the day-ahead market is proposed. The time-sequential Monte Carlo simulation is used to model the chronological characteristics of corresponding reliability network equivalents. A simplified method is also developed in the simulation procedures for improving the computational efficiency. The proposed technique can be used to evaluate customers' reliabilities considering high penetration of wind power during the power system operation in the deregulated environment.