Operation Of Large Power Systems Research Articles

Mitigation of Saturated Cut-Sets During Multiple Outages to Enhance Power System Security

Ensuring reliable operation of large power systems subjected to multiple outages is a challenging task because of the combinatorial nature of the problem. Traditional approaches for security assessment are often limited by their scope and/or speed, resulting in missing of critical contingencies that could lead to cascading failures. This paper proposes a two-component methodology to enhance power system security. The first component combines an efficient algorithm to detect cut-set saturation (called the feasibility test (FT) algorithm) with real-time contingency analysis (RTCA) to create an integrated corrective action (iCA), whose goal is to secure the system against cut-set saturation as well as critical branch overloads. The second component only employs the results of the FT to create a relaxed corrective action (rCA) to secure the system against post-contingency cut-set saturation. The first component is more comprehensive, but the latter is computationally more efficient. The effectiveness of the two components is evaluated based upon the number of cascade triggering contingencies alleviated, and the computation time. The results obtained by analyzing different case-studies on the IEEE 118-bus and 2000-bus synthetic Texas systems indicate that the proposed two-component methodology successfully enhances the scope and speed of power system security assessment during multiple outages.

Quantifying robustness of Type 4 wind power plant as reactive power source

The quantification of reactive power reserves can be essential for transmission system operators for the secure operation of large power systems with high share of renewables. Reactive power support from renewable energy sources needs to be included in reactive power reserve estimation. The reactive power capability of variable renewable energy sources like wind power plants depends on active power production. The stochastic nature of wind speed, and thereby active power production, makes reactive power reserve estimation quite complex. This article proposes a novel methodology to estimate reactive power reserve of wind power plants, taking the uncertainties such as the active power fluctuation, the technical availability of wind turbines as well as the on-load tap changer position of wind power plant transformers into account. The methodology incorporates the definition and determination of robustness index for wind power plant as a reactive power source. The proposed methodology is evaluated on a test system, by assessing the impact of the robustness index on long-term voltage stability. The results show that the choice of an appropriate time period for assessment of wind power plant as a reactive power source is critical to have a high degree of confidence in reactive power reserve estimation. Furthermore, the investigation reveals the importance of considering the power fluctuation and availability in the estimation of the reactive power reserve. The presented case study shows that ignoring fluctuation and availability can lead to overestimation of maximum power transfer, resulting in wrong assessment of the power system security. The proposed methodology can be used by the transmission system operators to quantify the reactive power reserve in real-time and allow better integration of wind power plants in voltage stability assessment studies.

AGC of a multi sources power system with natural choice of power plants

This paper presents an application of optimal control theory in multi sources power system by considering natural choice of power plants participating in automatic generation control (AGC) scheme. However, for successful operation of large power system, the natural choices of generation suitable for AGC system are hydro and thermal power plants since gas and nuclear power plants are rarely participates in the AGC scheme. Therefore, this work presents design and implementation of proportional integral (PI) structured optimal AGC controller in the presence of hydro and thermal power plants by using state vector feedback control theory. Moreover, various case studies are identified to obtain: (i) Cost aspects of physical realization of optimal AGC controller, (ii) Closed loop system stability margin through patterns of eigenvalues and (iii) System dynamic performance. Further, results have shown that when optimal AGC scheme is implemented in power system, the dynamic performance of power system is outstanding over those obtained with genetic algorithms (GAs) tuned PI structured AGC controller. Besides, with optimal AGC controller, cheaper cost of control structure, increased in system closed loop stability margin and outstanding dynamic performance of power system have been found when lessening in hydro generation is replaced by generation from thermal power plants for various case studies under investigation.

Short-Term Wind Power Forecasting Using Artificial Neural Networks for Resource Scheduling in Microgrids

Use of wind power as one of renewable resources of energy has been growing quickly all over the world. Wind power generation is significantly vacillating due to the wind speed alteration. Therefore, assessment of the output power of this type of generators is always associated with some uncertainties. A precise wind power prediction aims to support the operation of large power systems or microgrids in the scope of the intraday resources scheduling model, namely with a time horizon of 5-10 minutes, and this can efficiently uphold transmission and distribution system operators to improve the power network control and management. A Shortterm ANN based wind power prediction model, for day-ahead energy management and scheduling in microgrids, is developed utilizing a real database of 12 months with 10 minutes time interval data from measured information of online supervisory control and data acquisition (SCADA) of Goldwind microgrid wind turbine system (Beijing, China) as well as Numerical Weather Prediction (NWP). The ANN predicted wind power has been compared with the actual power of Goldwind wind turbine system. The predicted wind power has shown acceptable agreement with the actual power output that has been recorded by the SCADA which confirms the robustness and accuracy of the ANN wind power forecasting model developed in this research paper.

Survey on power system stabilizers control and their prospective applications for power system damping using Synchrophasor‐based wide‐area systems

AbstractPower system oscillation damping remains as one of the major concerns for secure and reliable operation of large power systems, and is of great current interest to both industry and academia. The principal reason for this is that the inception of poorly‐damped low‐frequency inter‐area oscillations (LFIOs) when power systems are operating under stringent conditions may lead to system‐wide breakups or considerably reduce the power transfers over critical corridors. With the availability of high‐sampling rate phasor measurement units (PMUs), there is an increasing interest for effectively exploiting conventional damping control devices, such as power system stabilizers (PSSs), by using these measurements as control input signals. In this paper, we provide a comprehensive overview of distinct elements (or “building blocks”) necessary for wide‐area power system damping using synchrophasors and PSSs. These building blocks together shape a tentative methodical framework, and are disposed as follows: (1) fundamental understanding of the main characteristics of inter‐area oscillations, (2) wide‐area measurement and control systems (WAMS and WACS) and wide‐area damping control (WADC), (3) advanced signal processing techniques for mode property identification, (4) methods for model‐based small‐signal analysis, (5) control input signals selection, and (6) methods for PSS control design. We also describe the latest developments in the implementation of synchrophasor measurements in WAMS and WACS as well as their prospectives for WADC applications. This paper serves both to abridge the state‐of‐the‐art in each of these elements, and to accentuate aspiring ideas in each building block. Copyright © 2011 John Wiley & Sons, Ltd.

Control of Large Power Systems Based on Situation Recognition and High Speed Simulation

The operation of large power systems places an increasing importance on the security of the system which must be evaluated in steady state, transient, and long term dynamic situations. A method based on situation and high speed simulation for on-line security computations is proposed and analyzed. The method combines the advantages of high speed hybrid computer simulation and pattern recognition methods, and, at the same time, has the flexibility of a pure digital simulation.

Signal and supervision circuits for carrier-current communications

Carrier-current equipment has become an important adjunct to the operation of large power systems. This article describes some signaling and supervisory trunking systems and illustrates how they are applied to carrier-current transmission.

Telephone Communication over Power Lines by High Frequency Currents

Communication is a matter of vital importance in. the operation of large power systems. The difference between ordinary wire communication and communication over high voltage power lines is discussed. The necessity for using energy levels greatly in excess of that commonly used on ordinary wire lines is indicated. The importance of selecting and utilizing only those circuit elements which are inherently stable is discussed. The superior stability of the two frequency system of duplex is brought out. A standard 250-watt communication equipment is described in detail. The great value of the heterodyne principle for calling is noted. The theory of antenna coupling is developed beginning with elementary principles. Several numerical examples are given to show the application of the theory. It is shown that the efficiency of antenna coupling is quite high contrary to the general opinion prevailing at present. A brief description of the propagation of high frequency currents over wires together with some of the principal equations is given. Tests are given which show a close agreement with accepted line theory. A simple method of determining line characteristic resistance and method of determining the effective line resistance is described. This method is applied to ground return circuits and discloses the existence of considerable resistance per mile in the ground return path.