Showing papers in "IEEE Power & Energy Magazine in 1994"

Steady-state analysis of self-excited induction generators

Abstract: Two solution techniques for the steady-state analysis of a self-excited induction generator (SEIG) are presented in this paper. The first technique employs a novel parameter elimination procedure to yield a 7th-degree polynomial in the per-unit frequency, numerical solution of which enables the performance of the SEIG to be determined. The second technique employs symbolic programming for the derivation and solution of the the high-order polynomial. The symbolic programming technique is further extended to the analysis of a voltage compensated SEIG using long-shunt connection. Very good agreement between experimental and computed results have been obtained on a 2 kW laboratory machine. >

Practical on-line partial discharge tests for turbine generators and motors

Abstract: Several utilities have found partial discharge testing to be very useful for identifying motors or generators with deteriorated stator winding insulation. Such partial discharge tests are sensitive to problems associated with overheated insulation, loose stator bars, and pollution, all of which can cause in-service failures with long associated outages and high repair/rewind costs. Unfortunately, the partial discharge test is not widely applied since present test methods require considerable skill to perform, and/or require machine outages. These problems are due to the stator winding partial discharges being masked by high levels of internal and external electrical noise. The authors describe how partial discharge tests have now been developed which eliminate the effect of noise, thus allowing plant personnel to perform the test without any machine outage. >

Calculation of UMP in induction motors with series or parallel winding connections

Abstract: This paper presents a general analytical method for determining the unbalanced magnetic pull (UMP) produced in three-phase induction motors with an eccentric rotor. The model uses the conformal transformation technique coupled to a winding impedance approach that is capable of accommodating any stator winding connection. The paper examines the influence of using parallel stator winding paths as a means of reducing the resultant UMP (static and pulsating). The results clearly demonstrate the significant reduction of static UMP of a typical stator winding with parallel paths together with the unbalanced winding currents that are produced. >

Improvement of induction motor drive systems supplied by photovoltaic arrays with frequency control

Abstract: The overall efficiency of an induction motor drive system, powered by a PV array, drops significantly when the insolation condition varies away from its nominal level. This problem can be overcame using a control method in which the frequency of the inverter's PWM control signal is adjusted according to the insolation and temperature conditions. The motor speed, and therefore, the power delivered to the load, are adjusted by controlling the inverter's frequency. This eliminates the mismatch between the maximum power that is available from the source and the power that is required by the load. Simulation results presented in this paper show that using the proposed control system allows the induction motor drive system to maintain its optimum efficiency and deliver consistently more power to the load when insolation and temperature vary from the nominal level. This method also offers an improvement in the system stability. >

A model to determine the degree of penetration and energy cost of large scale utility interactive photovoltaic systems

Abstract: The objective is to determine the value of photovoltaic (PV) energy when large PV systems are incorporated into the electric utility generation mix. Performance analysis shows that hydro availability, generation mix, maintenance schedules, ramping rates, fuel costs, spinning reserve requirements, PV power fluctuations, and geographical diversification are among the major factors that influence the economic and operational value of PV systems for large-scale applications. Economic analysis of various PV systems shows that PV energy cost (c/kWh) depends primarily on the PV capacity factor and capital cost, while the level of PV penetration is influenced by system characteristics. It was found that for a $2000/kW capital cost, the energy costs are 15.3 c/kWh and 1.4 c/kWh, for 10.55% and 25% capacity factors, respectively. Additionally, the study shows that the breakeven cost for the PV system ranges from $1211/kW to $361/kW, depending on the resource availability, generation mix, and fuel costs. >

Photovoltaic applications

Abstract: Photovoltaic (PV) systems are still in the evolutionary phase and are expected to grow for several decades to come. Fueled by environmental considerations, interest in PV is showing a healthy rise both in the minds of the public and in the planning realms of the electric power community. In recognition of this, the Energy Development Subcommittee of the IEEE Energy Development and Power Generation Committee organized a Panel Session on photovoltaics applications at the 1993 International Joint Power Generation Conference (JPGC '93) held in Kansas City, Missouri, USA. Summaries of the four presentations are assembled here for the benefit of the readers of IEEE Power Engineering Review.

Analysis of wind driven grid connected induction generators under unbalanced grid conditions

Abstract: A wind driven induction generator feeding power to the grid has been analyzed under the abnormal condition of unbalanced grid voltages. Using the symmetrical component and double revolving field theory, appropriate equivalent circuits and model equations have been derived for the generating mode with suitable realistic modifications. It is emphasized that the active and reactive power components and their directions for both positive and negative sequence systems need to be properly identified in order to obtain the cumulative response of the generator under different wind power conditions. In view of the fact that the reactive power is drawn from the grid while the active power is fed into the grid, the extent of variations in power fed to the grid and the reactive VAr due to unbalanced grid voltages for different wind power conditions need to be estimated to provide guidelines in the design and operation of the wind energy conversion system. Both experimental and theoretical results for a 3.7 kW laboratory model have also been presented, to validate the theoretical formulations, extendable to large units. Extensive data have been presented and discussed for a 55 kW unit installed in site. >

Power quality solutions

Abstract: The proliferation of microelectronic processors in a wide range of equipment, from home VCRs and digital clocks to automated industrial assembly lines and hospital diagnostic systems, has increased the vulnerability of such equipment to power quality problems. These problems include a variety of electrical disturbances, which may originate in several ways and have very different effects on various kinds of sensitive loads. Responding to these needs and opportunities, EPRI is accelerating an already wide-ranging program of research to study and solve power quality problems. Surveys are under way to better understand the causes and effects of power disturbances, as seen both on utility systems and at individual customer sites. The power quality characteristics of important categories of sensitive equipment, such as personal computers, are being measured, and more-advanced power conditioners are being developed for use by customers. EPRI is also developing advanced power electronic controllers for use on utility distribution systems. >

Chile: Pioneer in deregulation of the electric power sector

Abstract: This article examines the deregulation of the electric power sector in Chile. Chile was the leader in Latin America in the restructuring of the electric power sector, and its case merits particular analysis. Although a small system (70% of installed capacity is hydroelectric with 2,800 MW maximum demand in 1993), its development has been observed with interest by many institutions, particularly by the World Bank and most recently by other Latin American countries, and several countries have followed its steps. The Chilean 1982 electricity law was a worldwide pioneer in deregulating the electric power sector to create market conditions where generators compete to provide electrical energy to large consumers, sharing a transmission system open to all and paying fees for that system. The law formalized what had taken place in the country since 1978, several years before market approaches were formulated in the US and implemented in the United Kingdom.

A novel vector control hysteresis current controller for induction motor drives

Abstract: In this paper, a novel vector control hysteresis current controller for induction motor drives is proposed. Coordination of three phase switches is made in the d-q phase plane. In addition to the current error, information of the current error derivative is further employed so that one can take full advantage of adding the zero voltage vector for reducing the switching frequency. A simple hardware implementation is also proposed such that merits of the conventional hysteresis current controller can still be kept. The theoretical basis and some simulation and experimental results are also covered in this context. >

Small SMES technology and cost reduction estimates

Abstract: Superconducting magnetic energy storage (SMES) has been under development for electric system applications for some time. Large units (/spl ges/10 MWh) have been designed for electric load management. Small systems ( >

Practical implementation of the SCADA+AGC/ED system of the hunan power pool in the central China power network

Abstract: To accomplish the dispatching automation of the Hunan Power Pool (HPP), a supervisory control and data acquisition and automatic generation control/economic dispatch (SCADA+AGC/ED) system supplied by Systems Control in the USA was imported by the Hunan Power Dispatch Control Center. In December 1990 the practical implementation acceptance test for the new system was completed. The new system is the first system completed to use closed loop control of AGC in the power pools of China. This paper reviews the background of developing the new system, and describes implementation schemes and operation tests of AGC. At the same time, the Constant Net Interchange (CNI) mode of AGC in the HPP is also discussed in detail, and finally the economic benefits and the improved operation quality after AGC is in operation are described. >

A graphical user interface for design, simulation, and analysis of power plant electrical auxiliary systems

Abstract: An interactive graphical user interface (GUI) package for the design, simulation and analysis of a power plant electrical auxiliary system is presented in this paper. The purpose of this package is to assist the engineer in performing nonreal-time, what-if, analysis in an interactive and intuitive environment. The package, AUXSYS, is capable of performing load flow and motor starting simulations. It provides a graphical interface for designing the one-line diagram of the plant and analyzing the output of the simulations. It is currently used for modelling Wisconsin Electric Power Company's (WEPCO) power plant electrical auxiliary systems and is implemented for use on PCs. >

Adaptive multi-layer self-tuning high performance tracking control for DC brushless motor

Abstract: Adaptive control for high performance drive systems has become an important subject of research. In applications such as robotics, actuation, and manipulation, the rotor of the electric motor should follow a pre-selected track at all time. The tracking accuracy should not be affected by parameter uncertainties, unknown load variations, or sudden external disturbances. In this paper two schemes of adaptive control are developed and tested for a DC brushless motor. The first scheme is a single-layer self-tuning controller based on the generalized minimum variance theory. The second is a multi-layer adaptive controller consisting of a self-tuning control layer and a supervisory control layer. The supervisory controller continuously monitors the status of the system parameters, the structure of the controller, and the motor performance. A laboratory setup is constructed to test the proposed methods. Laboratory results show that the multi-layer controller is capable of achieving the tracking process with a high degree of accuracy, even in the presence of large and sudden disturbances. >

Buying and selling power in the age of competition

Abstract: The American electric power industry is currently in the throes of striving for workable competition. Driven by the converging forces of deregulation, technological revolution, and evolving customer expectations, electric utilities are having to compete as never before at both the wholesale and retail levels. At times, the transition has been particularly wrenching, with some utilities going through painful internal restructuring and others being caught up in external consolidation. Increasingly, the key to success in this more competitive environment is anticipating and actively responding to the forces that are shaping the new markets for electric power. Here, the author describes how such market management is the subject of pioneering research being conducted in EPRI's Utility Resource Planning and Management Program. On the wholesale side, this research centers on the development of powerful analytical methods to support utility decisions regarding new opportunities in the bulk power market. Research on retail market management is concentrated on developing innovative price-differentiated services that can enhance the value of electricity to customers and also foster a utility's long-term financial competitiveness. >

Risk assessment of low-level exposures

Abstract: This presentation contends that in cancer-risk assessments employed by the US Environmental Protection Agency, assumptions are made that exaggerate risks by large factors. Among these is an important but unproven hypothesis that results obtained by administering huge doses of substances are predictive of effects of minuscule doses. To calculate effects of small doses, a linear extrapolation from large doses to zero is employed. The routine use of this procedure implies that pathways of metabolism of large doses and small doses are identical. It implies that mammals have no defense against effects that injure DNA. It implies that no dose, however small, is safe. Examples of instances in which these assumptions are invalid are becoming numerous.

A generic DSP-based real-time simulator with application to hydrogenerator speed controller development

Abstract: This paper presents the features and evaluation of a digital signal processor/personal computer-based simulator which allows the simultaneous simulation of two linear systems in real time. A desire to gain the ability to evaluate hydrogenerator governors (speed controllers) in forms completely equivalent to that which could be used to control actual hydrogenerators is the primary motivation for this work. The simulator is designed so that one linear system may be conceptualized as an error controller while the second system may be thought of as a plant under control. The simulator is specialized in that it allows direct entry of the hydrogenerator system parameter values of one of two linearized hydrogenerating system plant models. An option to enter the gains of a generic PID controller also exists. This PID controller may be utilized to simulate a governor for a hydrogenerator, thus allowing the real-time simulation of a closed-loop speed-controlled hydrogenerating system. Simulation accuracy is established by comparing computed results to those computed by an accepted "standard" software package. An IBM-compatible personal computer and a modified Texas Instruments TMS320C30 digital signal processor evaluation module are the primary hardware used. >

Stability and nonlinear dynamics in power systems

Abstract: Power systems are characterized by nonlinear dynamics, and unusual and unexpected behavior has been observed in both simple and complex networks. System behavior is expected to become increasingly complicated because of such factors as greater interconnection, the implementation of high-speed electronic power control devices and wheeling requirements. The author describes how, because other nonlinear systems are known to exhibit chaotic behavior, exploratory research is being conducted to determine if the potential for chaos exists in power networks and, if so, how to avoid or control such behavior. By increasing the fundamental understanding of power system dynamics, these investigations could lead to substantial economic benefits. They could reduce the potential for catastrophic failure as well as allow secure network operation closer to performance margins. >

Photovoltaic power system applications

Abstract: This article is an overview of Photovoltaic Power System applications. Photovoltaic power system range in size from watts to megawatts. They are the most modular of all electric power generating systems. PV systems produce electricity for a wide variety of applications. They can be placed in almost any location in the world, and beyond when space applications are included. When PV power for watches, calculators, and similar consumer electronic products is included in the definition of PV power system, system sizes are even smaller and applications more numerous.

Tidal power plants in Russia

Abstract: This article examines the performance of tidal power plants in Russia and the expansion of tidal plant to new sites. The topics of the article include remote construction and transport techniques, pilot plant performance, economics and payback, and a review of global tidal power plant designs that are on hold due to economic problems relating to the global economy.

Expert system applications in power system planning and operations

Abstract: This article addresses the use of software tools by engineers, operators, and planners to handle complex issues in less amounts of time. The topics of the article include applications of artificial intelligence (AI) in power system operations applications such as customer restoration and fault testing, voltage and VAR dispatch, dynamic security analysis, voltage collapse, control center load management assistance, optimal power flow, and power system restoration; and applications in power system planning such as training, data verification, stability studies, load forecasting, outage scheduling, ranking of alternatives, power transaction evaluation, and evaluation of third-party generation alternatives.

What role can neural networks play in power system engineering

Abstract: This article discusses the application of the layered perceptron form of artificial neural network (ANN) to solving problems in the field of energy production. The topics of the article include the ANN learning process, problems with back error propagation, scaling, diminished learning, and neural network application to power systems in areas of regression, classification, and combinatorial optimization.

Identification of synchronous machine parameters using broadband power excitations

Abstract: An interactive Graphical User Interface (GUI) package for the design, simulation and analysis of a power plant electrical auxiliary system is presented in this paper. The purpose of this package is to assist the engineer in performing non real-time, what-if analysis, in an interactive and intuitive environment. The package, AUXSYS, is capable of performing load flow and motor starting simulations. It provides a graphical interface for designing the one-line diagram of the plant and analyzing the output of the simulation. It is implemented for use on PC's. A power plant electrical auxiliary system is similar to a large power system and can be analyzed via load Bow, fault study etc. The purpose of AUXSYS is to provide an easy and intuitive way for engineers to study the electrical systems of power plants. It provides an interface for the analysis of power plants where the engineer can interact with a graphical model of the plant and analyze the plant through direct manipulation of the model. We model the steps taken by an engineer in studying the plant as (a) design, (b) simulation, and (c) analysis. In the design part, the visual representation of the devices and the configuration of the plant are created or modified. The simulation part approximates the behavior of the plant for the given configuration. In the analysis part, the results of the simulations can be viewed. Iterating through the above steps enables the engineer to perform \"what if\" studies on the plant. To accurately simulate and analyze the electrical behavior of the auxiliary system, the effects of the main network needs to be considered. The power plant electrical auxiliary system can be viewed as an isolated system with boundary lines connecting the plant to the main network. To this end, we separated the plant one-line diagram and the boundary one-line diagram. The boundary system can be configured similarlyto the plant and can be used to simulate different loading patterns on the plant. AUXSYS consists of six modules. These are: symbol builder, design, load flow simulation, motor starting simulation, load flow analysis and motor starting analysis. The user interacts with the design and the analysis modules. The simulation modules are invoked transparent to the user The symbol builder module is used to design the visual representation(s) (icons) of a device and maintain the catalog of the devices used in designing the one-line diagram. Typically, the representation of the devices will be designed once and reused in multiple one-line diagrams. The design module is used to edit the configuration of the plant and boundary systems and interface to the simulation programs. The configuration of system is defined by the schematic of the one-line diagrams, the data associated with the components of the system and the state of the devices. The simulation modules are invoked on the plant and boundary configuration from the design module. The data required for running the simulation is generated automatically from the current configuration of the plant and boundary systems. The load flow simulation of the plant is achieved using the fast decoupled load flow. The user is presented with a graphical output of the real and reactive convergence of the bus power mismatch during the simulation. The load flow analysis module displays the results of the simulation on the one-line diagram of the system. The results include bus voltages, generation, mismatch, line flows etc. The user can scroll through the plant and boundary one-line diagrams and view these results. AUXSYS provides for two methods of motor starting. These are the static and dynamic motor starting. The user chooses the motors, for which the motor starting simulation should be performed, interactively, in the design module. A maximum of four motors can be started per simulation. In static motorstarting, a load flow simulation is performed on the system, in which each motor load is multiplied by a constant factor. The output of the simulation is analyzed through the load flow analysis module. In the dynamic motor starting simulation module, the motors can be started either sequentially or simultaneously. The machine transients and subtransients can be studied with this module. In the dynamic motor starting analysis module, the variation of motor parameters (Y-axis) against time (X-axis) can be plotted and compared. This module allows for up to four different motor starting simulations to be compared at one time. The parameters that can be viewed include slip, speed, motor and load torque, current angle and magnitude, voltage angle and magnitude. AUXSYS is currently used to model Wisconsin Electric Power Company's power plants with wider deployment planned in the near future. The features of the package help engineers in the visual dissemination of information during the design, simulation and analysis of the power plant electrical auxiliary system.

Feasibility Studies of a Power Interconnection System for Central American Countries: SIEPAC Project

Abstract: The electrical systems of the Central American countries are linked by 230 kV ac weak border interconnections forming two separated subsystems. The first one includes Guatemala and El Salvador, and the other one comprises the systems of Honduras, Nicaragua, Costa Rica, and Panama. As a consequence, unrestricted energy exchanges among all countries are not possible. This article describes the SIEPAC project which consists of a 1,678 km long 500 kV ac power transmission line that would link the six electrical systems of the region through seven power substations (one for each country and two in Panama), installed close to the highest demand national centers and six control centers of energy (one for each country) to allow coordinated operation of the interconnection.This project also considers a set of complementary assets (230 ac power transmission lines into some countries and the border transmission line between El Salvador and Honduras, and various other equipment). The power transmission line will greatly reinforce the actual border interconnections, which have a reduced capacity of exchange and technical problems associated with the stability of a weak longitudinal system. On the other hand, economic savings for the region would be achieved, coming from a higher coordination level inmore » the operation and planning of their systems.« less

Issues in utility-interactive photovoltaic generation

Abstract: This article examines factors affecting the application of solar Photovoltaic Power Plants to their power grid. A utility considering the use of solar photovoltaic generation should consider the following issues: power conditioning, protection, islanding, intermittent output, and installation. PV generation, like many advanced electrical technologies, will at times require improved performance from the utility system. Operating and protection practices may have to change to accommodate PV. However, operating experience and studies show that PV generation will operate well with existing electric utility systems.

Transmission access raises unresolved economic issues

Abstract: The electric utility industry is in the process of gradual change from a fully regulated industry to one of partial deregulation. Instead of relying on regulation to achieve a fair and equitable price to the consumer for electric energy, the reliance is placed more and more on market forces, through competition, to provide wholesale energy at the best market price. Clearly, open transmission access is required to create a viable competitive wholesale market for new generation resources. This article describes four unresolved, or at least partially unresolved, issues associated with transmission access for wholesale wheeling. Wheeling has been defined as the use of a utility's transmission facilities to transmit power for other buyers and sellers. At least three parties are involved in a wheeling transaction: a seller, a buyer, and one or more wheeling utilities that transmit the power from the seller to the buyer. This article considers wholesale or bulk wheeling only, and does not consider retail wheeling. The four unresolved economic issues described in this article pertain to transmission access: actual cost of providing transmission services; methodology or methodologies used in evaluating the cost of wheeling; contract path versus the actual power flows of the wheel; and issues associated with the formation of transmission regions. >

Reorganization of the electric transmission system in Argentina

Abstract: The Argentine electric system was developed from isolated local services, and, as the years went by, it became a well-integrated grid. Except for some services in the southernmost region, the national interconnected system supplies electric power to final users throughout the country. The paper discusses: Argentine interconnected system; private companies and public service; electric power sector transformation; transmission network privatization; transmission rates; concession (license) contract; extensions and other transmission concessions.