Elgenanalysis of Large Electric Power Systems

The present work is based on developing a control strategy to mitigate the impact of reduced inertia due to significant DFIG penetration in a large power system. The paper aims to design a supplementary control for the DFIG power converters such that the effective inertia contributed by these wind generators to the system is increased. The paper also proposes the idea of adjusting pitch compensation and maximum active power order to the converter in order to improve inertial response during the transient with response to drop in grid frequency. Results obtained on a large realistic power system indicate that the frequency nadir following a large power impact in the form of generators dropping out is effectively improved with the proposed control strategy. The proposed control is also validated against the sudden wind speed change in the form of wind gust downs and wind ramp downs occurring in conjunction with the generators dropping out. A beneficial impact in terms of damping power system oscillations is also observed, which is validated by eigenvalue analysis. The affected mode is then excited with a large disturbance in time domain. The damping improvement observed in time domain and subsequent Prony analysis support the result obtained from eigenvalue analysis.

This paper presents a new efficient solution approach for solving the unit commitment schedule of thermal generating units of a realistic large scale power system. The approach is based on the equivalencing like concept of network reduction which reduces the number of units in the large power system to the lowest possible number according to their fuel/generation cost characteristics. The reduced system is then solved and from that overall solution to the original unit commitment problem of the entire system is obtained. Test results for real-life systems of up to 79 units and comparisons with results obtained using Lagrangian relaxation and truncated dynamic programming (DP-TC) are also reported.

This paper proposes approaches to estimate the dominant swing mode sensitivity by utilizing Wide Area Measurements. The proposed methods are suitable to situations where availability of information of system model and operating condition is limited to a subsystem in which the control action resides. Modal frequency and mode shape of the dominant swing mode are estimated from a Wide Area Measurement System (WAMS) based mode identification technique. This information is used along with the subsystem model for estimation of eigenvalue sensitivity. Such a scenario is indeed faced in large interconnected power systems, where effect of a control action in the subsystem on a dominant inter-area mode needs to be estimated before actual implementation. Analytical formulations of sensitivity are derived using special modal characteristics (identified based on simplified system models) and a hybrid representation of the system, in which the subsystem is treated as a controller in a feedback loop to the rest of the system. Case studies with detailed models of two area four machine and IEEE 16 machine 68 bus system validate these formulations.

This paper presents transient stability assessment of a large actual power system using the probabilistic neural network (PNN) with enhanced feature selection and extraction method. The investigated large power system is divided into five smaller areas depending on the coherency of the areas when subjected to disturbances. This is to reduce the amount of data sets collected for the respective areas. Transient stability of the power system is first determined based on the generator relative rotor angles obtained from time domain simulations carried out by considering three phase faults at different loading conditions. The data collected from the time domain simulations are then used as inputs to the PNN. An enhanced feature selection and extraction methods are then incorporated to reduce the input features to the PNN which is used as a classifier to determine whether the power system is stable or unstable. It can be concluded that the PNN with enhanced feature selection and extraction methods reduces the time taken to train the PNN without affecting the accuracy of the classification results.

As the electricity industry becomes increasingly competitive, knowledge concerning the capacity, constraints and reliability of the electric system will become a commodity of great value. Electricity markets can be fast changing; understanding the implications of these changes before others can give an important competitive advantage. Power systems, however, are characterized by extremely large sets of data that cover spatial, temporal and contingent dimensions. Therefore the focus of this mini-track is on the management and visualization of the information associated with power markets and power systems. This year there were four accepted papers. The first paper, “Visualization for Shipboard Power Systems” addresses power system visualization as applied to naval ships. The relatively smaller size of the ship power system, as compared to large land-based grids, allows for a detailed and geographical display of the individual power system components, such as generators, cables, switchboards, circuit-breakers, bus transfer switches, and loads. Geographical information provided for these components could be quite useful to assess the impact of faults due to either battle damage or material casualties. The paper presents the details of the visualization and information retrieval tools needed to provide this display. The second paper, “Animation and Visualization of Spot Prices via Quadratized Power Flow Analysis,” moves from displaying detailed device information for a small system to providing techniques for visualizing information about the prices in a large power system. The paper presents a new model for efficient calculation of spot prices, and then presents techniques for the animation and visualization of spot price evolution as the system operating point is changing. The computational method is based on the quadratized power flow approach, which casts the power flow problem as a set of quadratic equations. Once the power flow problem is solved to determine the operating point the spot prices are computed by a linear programming approach. The results are then visualized in a three-dimensional OpenGL display. The third paper in the mini-track, “Displaying Aggregate Data, Interrelated Quantities, and Data Trends in Electric Power Systems,” presents visualization techniques that have actually been implemented in the Tennessee Valley Authority control center to display SCADA information. The paper describes how advanced visualization techniques such as historical trend animations and three-dimensional displays can be used to clarify the complex relationships, aggregate subsystem characteristics, and emerging trends that describe the current state of the TVA system and help predict its future evolution. The last paper in the mini-track, “Data

A power system is composed of various components such as generators, transformers, transmission lines, switching devices and loads. They have their mathematical model and graphical representation. Sometimes, a power system’s change of topology occurs due to events like short circuits, lightning striking a transformer, or a reconfiguration of the transmission system. In this thesis, a new way of simulating large scale power systems is presented from the modeling point of view. In the literature, a lot of modeling methods and mathematical tools are available to tackle this subject. However, this thesis mainly focuses on the time domain simulation of large scale power systems - and in particular, transients which appear after a change of topology. A change of topology in electrical networks impact time domain simulations on two levels. The first impact is that it is necessary to update or re-compute the set of equations. The computation time of this action on the topology can be significant - especially for large scale power systems. The second impact of this change of topology is the transient that will occur. Usually, this change will impose to numerically compute fast oscillations in currents and voltages until they reach a new steady state...

The quality of power system operating need to assess maturity of small oscillation stability issues of regional power grid thoroughly, analysis level of operating, controller installation allocating and parameter optimization scheme from different develop stage of regional power grid accurately. The assessment scheme is based on damping torque analysis of real large scale power system. Small oscillation stability is to be evaluated through the mechanism of damping torque analysis with automatic voltage regulator and other power system stabilizers. By analyzing the characteristic of the link between damping torque provided or transferred through each generator and the oscillation mode detected in the power system, the maturity indice has been established. This indice may cover the information of the contribution of controllers towards the power system and the dispatching within each generator in power system. Practical application effects in a real large scale power grid indicates this assessment can thoroughly describe the action of control elements in the power grid, help to depict the whole picture of impact applying power system controllers. A novel maturity evaluation of small oscillation in power grid is presented.

This paper presents a combined optimization/reliability technique to evaluate the reliability of large power systems. It uses Monte Carlo simulation for the individual operation/failure random performance of elements of a power network. This simulation overcomes the difficulty in constructing the many possible states for large power systems of complex topology. A simplified power-flow representation of the power network is used and a network reduction is implemented to reduce the size of the power-flow problem, such that only the effective part of the network (for a given contingency) is retained. The control parameters are optimized in order to simulate practical contingency situations in which suitable controls are invoked to preserve, as much as possible, the continuity of supply. The optimization problem is solved by linear programming in which the generator powers are manipulated as optimization variables to maximize the load power supplied and subject to the power flow equations as well as upper and lower bounds on the optimization variables. The outputs of the performance simulation and the optimization problem are subsequently used to compute the system reliability indices. The paper describes the computerized algorithm as well as numerical results for the IEEE 118-bus power system to demonstrate the applicability of the algorithm to actual systems.

Over the last few decades several innovative ideas have been explored in the energy storage areas, ranging in size, capacity, design complexity, and targeted applications. Some of them are designed for large scale power system applications, others for smallor medium-scale renewable energy or hybrid power systems, while the others are designed to perform short-term energy storage ride through for critical infrastructure (communication systems, hospitals, military facilities, etc.). Energy storage has become an enabling technology for renewable energy applications, grid integration and enhancing power quality and stability in the power transmission and distribution, having a great potential to improve power grid quality and stability and to provide an alternative to fossil fuel-based energy generation. The major constraints for renewable energy penetration are the availability, intermittency, and variability, which can be addressed through energy storage. The energy storage choice depends on specific usage requirements, often incorporating several energy storage systems in order to increase system reliability, capacity, and supply security. In the electric power system, the renewable energy promise lies in its potential to increase grid efficiency, reliability, or in optimizing power flows and supporting variable power supplies. The parameters used in comparisons of various energy storage technologies include efficiency, energy capacity and density, run time, costs, system's response time, lifetime in years and cycles, self-discharge, and maturity of each energy storage technology. The most common energy storage technologies include compressed air, pumped hydro, batteries, fuel cells, flywheels, and super-capacitors. The last four are suitable for the medium scale applications. The chapter discussed energy storage technologies and gives an up to date comparative summary of their performances. After completing this chapter, the readers are able to understand the role, importance, configurations and topologies of energy storage systems, operation principles, characteristics, performances, and operation of major energy storage systems used in power systems, buildings, and industrial facilities. Another benefit is that readers are able to understand the critical role and necessity of energy storage systems in power and renewable energy systems, the differences between large-, mediumand small-scale energy storage systems, and how a system is selected on specific applications based on system characteristics and performances. Major energy storage technologies discussed in this chapter are compressed air energy storage, pumped hydropower storage systems, batteries, flywheels, hydrogen energy storage, fuel cells, supercapacitors, and superconducting energy storage systems. Thermal energy storage systems are covered in detail in the next chapter. This chapter provides comprehensive reviews of the energy storage technologies and gives an up to date comparative summary of their performances, characteristics, and applications.

Power System study and analyses are important parts of power system engineering. This innovative concept deals with a 132 kV Grid simulation in Electrical Transient Analyzer Program (ETAP). Existing power distribution system in Pakistan consists of approximately 6000 11 kV feeders, which are mainly analyzed by software FDR-ANA (Feeder Analyses). This software does not have capability to provide comprehensive analyses for integrated power system which is essential. This research paper focused on the detailed analyses and monitoring by using the most modern software ETAP, which performs numerical calculations of large integrated power system with fabulous speed besides, generating output reports. In a developing country like Pakistan it is first time that Off-line monitoring is made which includes current flowing in every branch, power factor, active and reactive power flow, harmonic distortion etc. of large power system. Based upon the recorded data obtained from an actual 132 kV grid which has been implemented in ETAP for Off-line monitoring and analyses.

As there is a huge growth in the renewable energy sources, the solar farm based power plants are getting more popular among all researchers. In the large power systems, the sudden variations in the load requirements are more common. The variations in the load lowers the power quality in the power system. This paper concentrates on the power quality improvement in 100kW solar based standalone power system. In order to improve the power quality in the large power systems, the FACTS devices such as Static Synchronous Series Compensator (SSSC), Static Shunt Compensator (STATCOM), Unified Power Flow Controller (UPFC) etc., are used. Here, the STATCOM is implemented to improve the voltage profile of the power system under varying load conditions. The Distribution Static Compensator (D-STATCOM) balances the deficiency of reactive power by maintaining the voltage profile in the system.

This paper provides an integrated algorithm to identify a cutset for a large power system for the application of a slow coherency based controlled islanding scheme. Controlled islanding is employed as a corrective measure of last resort to prevent cascading outages caused by large disturbances. The large scale power system is represented as a graph and a simplification algorithm is used to reduce the complexity of the system. Generators belonging to the same slowly coherent group are collapsed into a dummy node, and a graph partition library is used to split the graph into a given number of parts. Some extra islands formed by the partition library are merged into their adjacent large islands and the original cutset of the actual power system is recovered from the highly simplified graph. A software package was developed to test the efficiency of the algorithm, and dynamic simulations were run on the WECC system to verify the effectiveness of the cutset obtained. The WECC system has more than 15 000 buses and 2300 generators. Detailed steps to develop an islanding strategy for a specified contingency for a large system are described in this paper.

Large power systems proposed for future space missions imply higher operating voltage requirements which, in turn, will interact with the space plasma environment. The effects of these interactions can only be inferred because of the limited data base of ground simulations, small test samples, and two space flight experiments. This report evaluates floating potentials for a 100 kW power system operating at 300, 500, 750, and 1000 volts in relation to this data base. Of primary concern is the possibility of discharging to space. The implications of such discharges were studied at the 500 volt operational setting. It was found that discharging can shut down the power system if the discharge current exceeds the array short circuit current. Otherwise, a power oscillation can result that ranges from 2 to 20 percent, depending upon the solar array area involved in the discharge. Means of reducing the effect are discussed.

The article proposes a power system fault-recognition technique founded on waveform analysis to identify and categorize short circuit faults in large power systems. The main criticism against waveform-based approaches is their huge computational burden and relatively slow processing, making them unsuitable for on-line applications. This article efficiently handles the computational load by applying a novel zone partitioning concept, where a large power system is partitioned, forming smaller hypothetical zones with fewer number of buses and lines. Crude determination of fault zone is first performed by a neural network (NN)-based zone classifier. A succeeding module of classifier, then determines the exact fault nature and its precise location within a hypothetical zone. Transient recorders installed at optimal monitoring buses, in each partitioned zone, collect the preliminary wave-data, which is then passed-on to an extended Kalman filter (EKF)-based feature extraction module, to filter-out relevant fault features. The EKF-NN combination is found to be highly efficient and precise in determining fault nature and location when tested on WECC-200-bus practical system. Hypothetical-zone partitioning has been established as a highly efficient technique, reducing the computation burden and CPU usage considerably, and rendering the scheme suitable for on-line implementation. The method also improved the fault-recognition accuracy phenomenally.

Nonlinearity of power system is always one of the difficulties when dealing with dynamic simulation of power systems. Solving differential-algebraic equations representing power systems are difficult without losing nonlinearity, especially for large power systems. This thesis shows an alternative method to solve nonlinear dynamical power system by producing a purely differential representation of the power systems. This new representation converts the algebraic equations to differential equations in order to have an absolute differential system. By using Runge-Kutta algorithm to solve this differential system, the results of the power system simulations are compared to trapezoidal integration algorithm commonly used to solve the differential-algebraic equations. In this thesis, IEEE 14-bus system and IEEE 118-bus system are tested with both classical generator model generator model and two-axis generator model in MATLAB. The proposed algorithm shows significantly faster convergence comparted to trapezoidal integration method in larger power systems. It is a great improvement to shorten the simulation time in while keeping the same accuracy in large power systems.