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We're Hiring! Help Center; less. pdf. Understanding-Facts-Narain-G-hingorani. pdf. Pages Flexible AC transmission systems. I. Gyugyi, Laszlo. II. Title. Flexible AC Transmission Systems (FACTS) and Custom Pcwer lines. In. , lesforgesdessalles.info G. Hingorani introduced the concept of Flexible AC Trans- mission. Narain G. Hingorani. Hingorani Power Electronics. WHAT IS A FLEXIBLE AC TRANSMISSION SYSTEM FACTS? Transmission and distribution.
For the voltage-sourced converter, its ac output voltage is controlled such that it is just right for the required reactive current flow for any ac bus voltage dc capacitor voltage is automatically adjusted as required to serve as a voltage source for the converter. Arslan Erinmez, Dr. Instead of continuous control of capacitive impedance, this approach of switching inductors at flring angle of 90 degrees or degrees but without firing angle control, could reduce cost and losses of the Controller [Figure 1. Full Name Comment goes here. Old Password. When the storage capacity -ot ttt" dc capacitor is small, and there is no other power source connected to it, the converter cannot supply or absorb real power for much more than a cycle' The ac output voltage is maintained at 90 degrees with reference to the ac current, leading or Lgging, und ttt" converter is used to absorb or supply reactive power only.
Author Bios About the Authors He is a retired vice president of Electrical Systems at EPRI and provides consulting services that help utilities plan and purchase power electronics technology. His research covers a broad range of power electronic circuits and systems.
In collaboration with B. Pelly, Dr. Subsequently, he has focused on the development of new power electronic technologies for electric transmission and distribution systems, and has pioneered the converter-based approach for FACTS.
Gyugyi has published more than 50 papers in the field and holds 76 U. He is a Fellow of the IEE. Free Access.
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Understanding facts-narain-g-hingorani 1. This book and other books may be purchased at a discount from the publisher when ordered in bulk quantities. Special Sales Hoes Lane P. Box Piscataway, NJ Fax: No part of this book may be reproduced in any form, nor may it be stored in a retrieual system or transmitted in any form, without written permission from the publisher.
Hingorani, Laszlo Gyugyi. Includes bibliographical references and index. ISBN 1. Flexible AC transmission systems. Gyugyi, Laszlo. H54 L This book is dedicated to all the engineers who have participated in the pioneering development of FACTS technology.
L Transmission Interconnections 1 1. L Power Flow in Parallel Paths 4 t. Introduction 8. L Basic Operating Principles and Characteristics 8. Controlled Braking Resistor 9. Design and Operation Aspects 9.
Preface Both authors of this book, Hingorani and Gyugyi, have been deeply involved in pioneering work in this-new technology of FlexibleACT. In fact, both have been involved in pioneering-uduun"", in many other applications of power electronics. FACTS is one aspect of the power electronics revolution that is taking place in all areas of electric "l: A variety of powerful semiconductor devices-nbt only offer the advantage of high speed and retiiUitity of switching but, more importantly, the opportunity offered by a variety of innovative circuit Joncepts based on these power devices enhance the value of electric energy.
This introduction is partly devoted to briefly conveying this perspective before discuJsing various specifics of Flexible AC Transmission' the subject matter of this book. After af, technololies from the transistor to microelectronics have revolutionized many aspects of our liies; there is no reason why power devices shouldn't have a significaniimpact on our lives as well, at least where energy is concerned.
The power electronics revolution is happening, and applications of power electronics will continue to expand. In the generatio. Photo voltaic generation and fuel cells require conversion of dc to ac. Generation with variable speed is necessary for the economic viability of wind and small hydrogenerators. Variable-speed wind glnerators and small hydrogen- erators require conversi: In any case, they serve the vital need-s of small, isolated loads where taking utility wires would be more expensive.
In thermal power plants, considerable energy could be saved with the use oi variable speed drives tor pumps and compressors. Batteries are widely used already for emergency power supplies. These require acldclac converters in the range of a few kilowatts to a few tens of megawatts.
On the other hand, variable speed hydrostorage requires converters of up to a few hundred megawatts. In the distribution area, an exciting opportunity called Custom Power enables at-the-fence solutions for delivery to industrial and commercial customers, value- added reliable electric service which is free from significant voltage reductions distor- tions, and over-voltages. It is now well known that voltage reductions of greater than 1.
The Custom Power concept incorporates power electronics Controllers and switching equipment, one or more of which can be used to provide a value-added service to the customers. In general, these Custom Power applications represent power electronics in the range of a few tens of kilowatts to a few tens of megawatts of conversion or switching equipment between the utility supply and the customer.
HVDC, a well-estab- lished technology, is often an economical way to interconnect certain power systems, which are situated in different regions separated by long distances over 50 km subma- rine or L km overhead line , or those which have different frequencies or incompati- ble frequency control.
HVDC involves conversion of ac to dc at one end and conversion of dc to ac at the other end. In general, HVDC represents conversion equipment sizes in the range of a hundred megawatts to a few thousand megawatts. In general, FACTS-the subject matter of this book and a relatively new technol- ogy-has the principal role to enhance controllability and power transfer capability in ac systems. On the end-use side, power electronics conversion and switching technology has been a fast-growing area for over two decades for a wide range of needs.
The fact is that electricity is an incredible form of energy, which can be converted to many different forms to bring about new and enabling technologies of high value. Conversion to pulses and electromagnetic waves has given us computers and communications. Conversion to microwave has led to microwave ovens, industrial processes, and radar.
In arc form, electricity serves its high value in arc furnaces, welding, and so on. Efficient lighting, lasers, visuals, sound, robots, medical tools, and of course, variable speed drives and the expanding need for dc power supplies are among the many other examples. Complementing the Custom Power technology is the whole area of power conditioning technology used by customers, under the term Power Quality. Uninter- ruptible power supplies UPS and voltage regulators represent a major growth area in power electronics.
In end use, the converter sizes range from a few watts to tens of megawatts. Considering the opportunities in power electronics through reduction in cost, size and losses, we are in an early stage of the power electronic revolution, and there is a bright future ahead for those who are involved. Potentially, there is a signiflcant commonality and synergism between the different areas of applications in generation, h Preface transmission, distribution, and end use.
FACTS technology, being new, has a lot to borrow from the power electronics conversion, switching, and control ideas in other areas. Also there is considerable overlap in the megawatt size, and hence there is potential use of standard components and subassemblies among many applications noted above and new ones in the future. Therefore, it is suggested that those individuals involved in power electronics not confine their interest to one narrow application area.
In this book the term "FACTS Controller" or just "Controller" with capital C, is used to generally charactefize the various power electronic circuit topologies or equipment that perform a certain function such as current control, power control, and so on.
Since the Power Semiconductor device is also referred to as a "device". The reason for using capital C is to distinguish Controllers from the controllers used for industrial controls. Besides, the word "device" sounds like a component, and the authors request the readers to use the word Controller for FACTS Controllers.
The authors' intent in writing this book on FACTS is to provide useful informa- tion for the application engineers rather than for a detailed post-graduate college course. Therefore, there is an emphasis on physical explanations of the principles involved, and not on the mathematically supported theory of the many design aspects of the equipment. Nevertheless, post-graduate students will also greatly benefit from this book before they launch into the theoretical aspect of their research.
This book will help post-graduate students acquire a broad understanding of the subject and a practical perspective enabling them to use their talents on real problems that need solutions. The book does not go into the details of transmission design and system analysis, on which there are already several good published books.
Chapter L: Engineers who wish to acquire sufficient knowledge to sort out various options, participate in equipment specifications, and become involved with detailed engineering and design will find significant value in reading the entire book in preparation for more lifelong learning in this area.
Chapter 2: In this book, sufficient material is provided for the FACTS application engineer for knowing those options. Those familiar with the subject of HVDC know that practically all the HVDC projects are based on use of thyristors with no gate turn-off capability, assembled into pulse converters, which can be controlled to function as a voltage-controlled rectifier ac to dc or as inverter dc to ac.
The voltage can be controlled from maximum positive to maximum negative, with the current flowing in the same direction; that is, power flow reverses with reversal of voltage and unidirectional current.
Current-sourced converters based on thyristors with no gate turn-off capability only consume but cannot supply reactive power, whereas the uoltage-sourced conuerters with gate turn-off thyristors can supply reactive power.
Such converters are based on devices with gate turn-off capability. In such unidirectional-voltage converters, the power reversal involves reversal of The voltage-sourced converters are described in Chapter 3 and the current-sourced converters in Chapter 4.
There are a wide variety of FACTS Controllers, and they have overlapping and competing attributes in enhancing the controllability and transfer capability of transmission.
The best choice of a Controller for a given need is the function of the benefit-to-cost consideration. Chapter 8 describes the combined series and shunt controllers, which are in a way the ultimate controllers that can control the voltage, the active power flow, and the reactive power flow.
There already is a large volume of published literature. At the end of each chapter, authors have listed those references that represent the basis for the material in that chapter, as well as a few other references that are directly relevant to that chapter. Narain G. Acknowledgments First and foremost, both authors acknowledge EPRI and its members, for providing an organization and support that enabled Dr.
Neal Balu, Ben Damsky, the late Dr. Gil Addis, Dr. Ram Adapa, Dr. Aty Edris, Dr. Harshad Mehta, and Dominic Maratukulam for competent management of many projects funded with various companies and universities. Karl Stahlkopf, Mark Wilhelm, and Dr. Robert Schainker, with special thanks to Ot.
In the s and s, John Rosa, Brian R. Pelly, and the late peter wooo were part of the early development efforts on circuit concepts, along with Eric Stacey who joined in these development efforts. Special acknowledgment is due to the present team that developed the converter-based FACTS Controller technology and whose work provided the basis for part of this book.
In particular, Dr. Colin Schauder, whose conceptual and lead-design work were instrumental in the practical realization of the high-power converter-based Controllers, and whose publications provided im- portant contributions to this book; Eric Stacey, whose participation generated many novel ideas and practical designs for power converter circuits; Gary L. Rieger, who effectively coordinated several joint development programs, and also read thi manu- script of chapters 5 through 8 and made suggestions to improve the text; Thomas ao xvll Kalyan Sen, Matthew Weaver, and others who contributed to the details of these projects.
A sincere, personal gratitude is expressed to Miklos Sarkozi, who constructed many of the illustrations used in this book. Special thanks are also due to Dr.
Kalyan Sen, who performed some computations and simulations for the book. Gyugyi wishes also to express his thanks to the executives of the Westinghouse Electric Corporation, who supported and funded the FACTS technology development, and to Siemens Power Transmission and Distribution who, having acquired Westing- house FACTS and Custom Power business, continue to embrace the technology and pursue its application to utility systems.
A particular debt of gratitude is extended to John P. Power Electronics Applications in Power Systems be utilized herein. Special credit is due to the pioneering utilities who are at the forefront of exploiting advanced technologies and maintaining high-level technical and manage- ment expertise to undertake first-of-a-kind projects.
Arslan Erinmez, of the National Grid Company, England, and their colleagues, and for their pioneering work in the large scale application of Static Var Compensators. They played a significant role in making those two utilities the largest users of SVCs, each with over a dozen installations. Under the ;hairmanship of Dr. Hingorani, and now Dr. In the Power Engineering In addition, the authors acknowledge Dr. Arslan Erinmez, Dr. Pierre-Guy Therond, Dr. Adel Hammad, Dennis Woodford, and Michael Baker for generating important source material to the author's knowledge base.
Special acknowledgment is due to Professor Willis Long for orchestrating material and a diverse faculty for an excellent course on FACTS for professional development at the University of Wisconsin. Hingorani further acknowledges Dr. Vic Temple for reviewing the chapter on power semiconductor devices, and his son Naren for his editorial help.
It would make a long list for the authors to acknowledge their professional colleagues working worldwide, who are among the leading innovators and contributors to the transmission and power electronics technologies.
This is done for economic reasons, to reduce the cost of electricity and to improve reliability of power supply. Transmission interconnections enable taking advantage of diversity of loads, availability of sources, and fuel price in order to supply electricity to the loads at minimum cost with a required reliability. In general, if a power delivery system was made up of radial lines from individual local generators without being part of a grid system, many more generation resources would be needed to serve the load with the same reliability, and the cost of electricity would be much higher.
With that perspective, transmission is often an alternative to a new generation resource. Less transmission capability means that more generation resources would be required regardless of whether the system is made up of large or small power plants.
In fact small distributed generation becomes more economically viable if there is a backbone of a transmission grid. The cost of transmission lines and losses, as well as difficulties encountered in building new transmission lines, would often limit the available transmission capacity. It seems that there are many cases where economic energy or reserve sharing is constrained by transmission capacity, and the situation is not getting any better.
In a deregulated electric service environment, an effective electric grid is vital to the competitive environment of reliable electric service. Chapter 1 f FACTS Concept and General System Considerations On the other hand, as power transfers grow, the power system becomes increas- ingly more complex to operate and the system can become less secure for riding through the major outages.
It may lead to large power flows with inadequate control, excessive reactive power in various parts of the system, large dynamic swings between different parts of the system and bottlenecks, and thus the full potential of transmission interconnections cannot be utilized.
The power systems of today, by and large, are mechanically controlled. There is a widespread use of microelectronics, computers and high-speed communications for control and protection of present transmission systems; however, when operating signals are sent to the power circuits, where the final power control action is taken, the switching devices are mechanical and there is little high-speed control. Another problem with mechanical devices is that control cannot be initiated frequently, because these mechanical devices tend to wear out very quickly compared to static devices.
In effect, from the point of view of both dynamic and steady-state operation, the system is really uncontrolled. Power system planners, operators, and engineers have learned to live with this limitation by using a variety of ingenious techniques to make the system work effectively, but at a price of providing greater operating margins and redundancies.
These represent an asset that can be effectively utilized with prudent use of FACTS technology on a selective, as needed basis. In recent years, greater demands have been placed on the transmission network, andthese demandswill continue to increasebecause of the increasingnumberof nonutil- ity generators and heightened competition among utilities themselves.
Added to this is the problem that it is very difficult to acquire new rights of way. Increased demands on transmission, absence of long-term planning, and the need to provide open access to generating companies and customers, all together have created tendencies toward less security and reduced quality of supply.
The FACTS technology is essential to alleviate some but not all of these difficulties by enabling utilities to get the most service from their transmission facilities and enhance grid reliability. It must be stressed, however, that formany of the capacity expansion needs, building of newlines or upgradingcurrent and voltage capability of existing lines and corridors will be necessary.
The possibility that current through a line can be controlled at a reasonable cost enables a large potential of increasing the capacity of existing lines with larger conductors, and use of one of the FACTS Control- lers to enable corresponding power to flow through such lines under normal and contingency conditions.
These opportunities arise through the ability of FACTS Controllers to control the interrelated parameters that govern the operation of transmission systems including series impedance, shunt impedance, current, voltage, phase angle, and the damping of oscillations at various frequencies below the rated frequency. These constraints cannot be overcome, while maintaining the required system reliability, by mechanical means without lowering the useable transmission capacity.
Mechanical switching needs to be supplemented by rapid-response power electronics. It must be emphasized that FACTS is an enabling technology, and not a one-on-one substitute for mechanical switches. Section 1,. Because all FACTS Controllers represent applications of the same basic technology, their production can eventually take advantage of technologies of scale.
Just as the transistor is the basic element for a whole variety of microelectronic chips and circuits, the thyristor or high-power transistor is the basic element for a variety of high-power electronic Controllers. FACTS technology also lends itself to extending usable transmission limits in a step-by-step manner with incremental investment as and when required.
A planner could foresee a progressive scenario of mechanical switching means and enabling FACTS Controllers such that the transmission lines will involve a combination of mechanical and FACTS Controllers to achieve the objective in an appropriate, staged investment scenario.
It showed that with an active Controller there is no limit to series capacitor compensation. Even prior to SVCs, there were two versions of static saturable reactors for limiting overvoltages and also powerful gapless metal oxide arresters for limiting dynamic overvoltages.
Research had also been undertaken on solid-state tap changers and phase shifters. However, the unique aspect of FACTS technology is that this umbrella concept revealed the large potential opportunity for power electronics technology to greatly enhance the value of power systems, and thereby unleashed an array of new and advanced ideas to make it a reality. Co-author Gyugyi has been at the forefront of such advanced ideas. FACTS technology has also provided an impetus and excitement perceived by the younger generation of engineers, who will rethink and re-engineer the future power systems throughout the world.
It is also worth pointing out that, in the implementation of FACTS technology, we are dealing with a base technology, proven through HVDC and high-power industrial drives. In ac power systems, given the insignificant electrical storage, the electrical generation and load must balance at all times. To some extent, the electrical system is self-regulating. If generation is less than load, the voltage and frequency drop, and thereby the load, goes down to equal the generation minus the transmission losses.
However, there is only a few percent margin for such a self-regulation. If voltage is Chapter 1 f FACTS Concept and General System Considerations propped up with reactive power support, then the load will go up, and consequently frequency will keep dropping, and the system will collapse.
Alternately, if there is inadequate reactive power, the system can have voltage collapse. When adequate generation is available, active power flows from the surplus generation areas to the deflcit areas, and it flows through all parallel paths available which frequently involves extra high-voltage and medium-voltage lines.
Often, long distances are involved with loads and generators along the way. An often cited example is that much of the power scheduled from Ontario Hydro Canada to the North East United States flows via the PJM system over a long loop, because of the presence of a large number of powerful low impedance lines along that loop.
There are in fact some major and a large number of minor loop flows and uneven power flows in any power transmission system. Without any control, power flow is based on the inverse of the various transmission line impedances. Apart from ownership and contractual issues over which lines carry how much power, it is likely that the lower impedance line may become overloaded and thereby limit the loading on both paths even though the higher impedance path is not fully loaded.
There would not be an incentive to upgrade current capacity of the overloaded path, because this would further decrease the impedance and the invest- ment would be self-defeating particularly if the higher impedance path already has enough capacity. Figure 1. Also, because power is elec- tronically controlled, the HVDC line can be used to its full thermal capacity if adequate converter capacity is provided.
Furthermore, an HVDC line, because of its high-speed control, can also help the parallel ac transmission line to maintain stability. However, HVDC is expensive for general use, and is usually considered when long distances are involved, such as the Pacific DC Intertie on which power flows as ordered by the operator.
By means of controlling impedance [Figure 1. Maximum power flow can in fact be limited to its rated limit under contingency conditions when this line is expected to carry more power due to the loss of a parallel line.
Section 1. Load Load For the impedances shown, the three lines would carry , , and L Mw, respectively, as shown in Figure 1'. Such a situation would overload line BC loaded at MW for its continuous rating of MW , and therefore generation would have to be decreased at B, and increased at A. If, however, a capacitor whose reactance is -5 ohms O at the synchronous frequency is inserted in one line [Figure 1.
It is clear that if the series capacitor is adjustable, then other power-flow levels may be realized in accordance with the ownership, contract, thermil limitations, transmission losses, and a wide range of load and generation schedules.
Although this capacitor could be modular and mechanically switched, the number of operations would be severely limited by wear on the mechanical components because the line loads vary continuously with load conditions, generation schedules, and line outages. Other complications may arise if the series capacitor is mechanically controlled. A series capacitor in a line may lead to subsynchronous resonance typically at Hz for a OOgzsystem.
This resonance occurs when one of the mechanical resonance frequencies of tle shaft of a multiple-turbine generator unit coincides with 60 Hz -5Ct MW MW load e MW d Figure L. If such resonance persists, it will soon damage the shaft. Also while the outage of one line forces other lines to operate at their emergency ratings and carry higher loads, power flow oscillations at low frequency typically 0.
If all or a part of the series capacitor is thyristor-controlled, however, it can be varied as often as required. It can be modulated to rapidly damp any subsynchronous resonance conditions, as well as damp low frequency oscillations in the power flow. This would allow the transmission system to go from one steady-state condition to another without the risk of damage to a generator shaft and also help reduce the risk of system collapse.
In other words, a thyristor-controlled series capacitor can greatly enhance the stability of the network. More often than not though, it is practical for part of the series compensation to be mechanically controlled and part thyristor controlled, so as to counter the system constraints at the least cost.
Similar results may be obtained by increasing the impedance of one of the lines in the same meshed configuration by inserting a7 A reactor inductor in series with line AB [Figure L2 c 1. Again, a series inductor that is partly mechanically and partly thyristor-controlled, it could serve to adjust the steady-state power flows as well as damp unwanted oscillations. As another option, a thyristor-controlled phase-angle regulator could be installed instead of a series capacitor or a series reactor in any of the three lines to serve the same purpose.
In Figure 7. As before, a combination of mechanical and thyristor control of the phase-angle regulator may minimize cost. The same results could also be achieved by injecting a variable voltage in one of the lines.
Note that balancing of power flow in the above case did not require more than one FACTS Controller, and indeed there are options of different controllers and in different lines. If there is only one owner of the transmission grid, then a decision can be made on consideration of overall economics alone. On the other hand, if multiple owners are involved, then a decision mechanism is necessary on the investment and ownership.
Assuming that ownership is not an issue, and the objective is to make the best use of the transmission asset, and to maximize the loading capability taking into account contingency conditions , what limits the loading capability, and what can be done about it? Basically, there are three kinds of limitations: It varies perhaps by a factor of 2 to 1 due to the variable environment and the loading history.
The nominal rating of a line is generally decided on a conservative basis, envisioning a statistically worst ambient environment case scenario. Yet this scenario Chapter 1 f FACTS Concept and General System Considerations occurs but rarely which means that in reality, most of the time, there is a lot more real time capacity than assumed.
Some utilities assign winter and summer ratings, yet this still leaves a considerable margin to play with. There are also off-line computer programs that can calculate a line's loading capability based on available ambient environment and recent loading history.
Then there are the on-line monitoring devices that provide a basis for on-line real-time loading capability.
These methods have evolved over a period of many years, and, given the age of automation typified by GPS systems and low-cost sophisticated communication services , it surely makes sense to consider reasonable, day to day, hour to hour, or even real-time capability information.
Sometimes, the ambient conditions can actually be worse than assumed, and having the means to determine actual rating of the line could be useful. Of course, increasing the rating of a transmission circuit involves consideration of the real-time ratings of the transformers and other equipment as well, some of which may also have to be changed in order to increase the loading on the lines.
Real- time loading capability of transformers is also a function of ambient temperature, aging of the transformer and recent loading history. Off-line and on-line loading capability monitors can also be used to obtain real time loading capability of transform- ers. Also, the transformer also lends itself to enhanced cooling.