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. PDF | First Page of the Article | ResearchGate, the professional network for Understanding FACTS-concepts and technology of flexible AC transmission systems [Book Review] . Hingorani and Gyugyi, they present a. ,greentinphalihang.tk G. Hingorani introduced the concept of Flexible AC Trans- mission book covers many analytical issues that affect the design of FACTS Con-.

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FACTS technology, being new, has xvi Preface current and not the .. Preface Both authors of this book, Hingorani and Gyugyi, have been. ELECTRICAL BOOK STORAGE. Home; BusinessĀ». Internet; Market Understanding FACTS By Hingorani. By Unknown Understanding. Understanding FACTS: Concepts and Technology of Flexible AC Transmission Narain G. Hingorani Ā· Laszlo Gyugyi About this book.

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.

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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.

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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.

Understanding FACTS: Concepts and Technology of Flexible AC Transmission Systems

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. Then there is the possibility of upgrading a line by changing the conductor to that of a higher current rating, which may in turn require structural upgrading.

Finally, there is the possibility of converting a single-circuit to a double-circuit line. Once the higher current capability is available, then the question arises of how it should be used. Will the extra power actually flow and be controllable? Will the voltage conditions be acceptable with sudden load dropping, etc.? Dielectric From an insulation point of view, many lines are designed very conser- vatively. Care is then needed to ensure that dynamic and transient overvoltages are within limits.

Modern gapless arresters, or line insulators with internal gapless arresters, or powerful thyristor-con- trolled overvoltage suppressors at the substations can enable significant increase in the line and substation voltage capability. Stability There are a number of stability issues that limit the transmission capa- bility.

These include: Therefore, discussion on these topics in this book will be brief, and limited to what is really essential to the explanation The FACTS technology can certainly be used to overcome any of the stability limits, in which case the ultimate limits would be thermal and dielectriC.

Locations I and 2 could be any transmission substations connected by a transmission line. Substations may have loads, generation, or may be interconnecting points on the system and for simplicity they are assumed to be stiff busses.

Er and E2 are the magnitudes of the bus voltages with an angle 6'between the two. The line is assumed to have inductive impedance X, and the line resistance and capacitance are ignored. As shown in the phasor diagram [Figure 1. The line current magnitude is given by: EylX, and lags Eyby 90" It is important to appreciate that for a typical line, angle D and corresponding driving voltage, or voltage drop along the line, is small compared to the line voltages.

Given that a transmission line may have a voltage drop at full load of. If we were to assume, for example, that with equal magnitudes of E1 and E2, and Xof 0. The current flow on the line can be controlled by controllingEyor Xor d. In order to achieve a high degree of control on the current in this line, the equipment required in series with the line would not have a very high power rating.

For example, a kv approximately kv phase-ground , A line has a three-phase throughput power of MVA, and, for a km length, it would have a voltage drop of about 60 kV. For variable series compensation of say,25Vo,the series equipment required would have a nominal rating of 0.

Voltage across the series equipment would only be 15 kV at full load, although it would require high-voltage insulation to ground the latter is not a significant cost factor. However, any series-connected equipment has to be designed to carry contingency overloads so that the equipment may have to be rated to Vo overload capability.

Nevertheless the point of this very simple example is that generally speaking the rating of series FACTS Controllers would be a fraction of the throughput rating of a line. If the angle between the two bus voltages is small, the current flow largely represents the active power.

Increasing or decreasing the inductive imped- ance of a line will greatly affect the active power flow. Thus impedance control, which in reality provides current control, can be the most cost-effective means of controllinp ttre powli flow. Note that for clarity the phasors are identified by their magni- tudes in this figure.

Active component of the current flow at E1 is: Et - E2cos 6 lX Thus, active power at the E1 end: Er, E2 sin 6 lX Reactive power at the. E, E1 sin 6 lX Reactive power at the E2 end: Thus, varying the value of Xwill vary P, Q6 and Q2in accordance with 1. Assuming that and E2 are the magnitudes of the internal voltages of the two equivalent machines representing the two systems, and the impedance X includes the internal impedance of the two equivalent machines, Figure 1.

Power then falls with further increase in angle, and finally to zero at 6: It is easy to appreciate that without high-speed control of any of the parameters Et Ez, Et - Ez, X and A the transmission line can be utilized only to a level well below that corresponding to 90 degrees.

Increase and decrease of the value of X will increase and decrease the height of the curves, respectively, as shown in Figure 1. For a given power flow, varying of X will correspondingly vary the angle between the two ends.

El or voltage phasor E2. However, it is seen from Figure 1. This also means that regulation of the -ugnitod" of voltage phasor E1 andlor E2has much more influence over the reactive power flow than the active power flow, as seen from the two current phasors corre- iponding to the two driving voltage phasors Et - Ez shown in Figure 1'3 e.

Current flow and hence power flow can also be changed by injecting voltage in series with the line. It is seen from Figure 1. It is seen that varying the amplitude and phase angle of the voltage injected in series, both the active and reactive current flow can be influenced.

Voltage injection methods form the most important portfolio of the FACTS Controllers and will be discussed in detail in subse- quent chaPters. I Control of angle with a Phase Angle Regulator, for example , which in turn controls the driving voltage, provides a powerful means of controlling the current flow and hence active power flow when the angle is not large. Since the current flow lags the driving voltage by 90 degrees, this means injection of reactive power in series, e.

This requires injection of both active and reactive power in series. Basic Types of FACTS Controllers 13 regulation with a shunt Controller can also provide a cost-effective means control both the active and reactive power flow between the two systems.

Series Controllers: In principle, all series Controllers inject voltage in series with the line.

Even a variable impedance multiplied by the current flow through it, represents an injected series voltage in the line. As long as the voltage is in phase quadrature with the line current, the series Controller only supplies or consumes variable reactive power.

Any other phase relationship will involve handling of real power as well. In principle, all shunt Controllers inject current into the system at the point of connec- tion. Even a variable shunt impedance connected to the line voltage causes a variable current flow and hence represents injection of current into the line. As long as the injected current is in phase quadrature with the line voltage, the shunt Controller only supplies or consumes variable reactive power.

Combined series-series Controllers: Or it could be a unified Controller, Figure 1. Note that the term "unified" here means that the dc terminals of all Controller converters are all connected together for real power transfer.

Combined series-shunt Controllers: In principle, combined shunt and series Controllers inject current into the system with the shunt part of the Controller and voltage in series in the line with the series part of the Controller.

However, when the shunt and series Controllers are unified, there can be a real power exchange between the series and shunt Controllers via the power link. As mentioned. The shunt Controller is therefore a good way to control voltage at and around the point of connection through injection of ieactive current leading or lagging , alone or a combination of aciive and reactive current for a more effective voltage control and damping of voltage oscillations.

This is not to say that the series Controller cannot be used to keep the line voltage within the specified range. After all, the voltage fluctuations are largely a "on. Nevertheless, a shunt controller is much more effeciive in maintaining a required voltage profile at a substa- tion bus.

Series Controller solution may require, but not necessarily, a separate series Controller for several lines connected to the substation, particularly if the application calls for contingency outage of any one line. However, this should not be a decisive reason for choosing-a shurit-conn""t"d Controller, because the required MVA sizeof the series Controller is small compared to the shunt Controller, and, in any case, the shunt Controller does not provide control over the power flow in the lines' On the other hand, ieries-connected Controllers have to be designed to ride through contingency and dynamic overloads, and ride through or bypass short circuit "orr"itr.

They can Le proticted by metal-oxide arresters or temporarily bypassed by solid-state devices when the fault current is too high, but they have to be rated to handle dynamic and contingency overload.

Thi above arguments suggist that a combination of the series and shunt Control- lers [Figures 1. For the combination of series and shunt Controllers, the shunt Controller can be a single unit serving in coordination with individual line Controllers [Figure l: This arrangement can provide additional benefits reactive power flow control with unified Controllers.

FACTS Controllers may be based on thyristor devices with no gate turn-off only with gate turn-on , or with power devices with gate turn-off capability. However' if the generated ac voltage or current is required to deviate from 90 degrees with respect to the line current or voltage, respectfuely, the converter dc storage can be augmented beyond the minimum required for the converter operation as a source of reaitive power only' This can be done at the converter level to cater to short-term a few tens of main In addition, another storage source such as a battery, superconducting magnet, or any other source of energy can be added in parallel through an electronic interface to replenish the converter's dc storage.

Any of the converter-based, series, shunt, or combined shunt-series Controllers can generally accommodate storage, such as capacitors, batteries, and superconducting magnets, which bring an added dimension to FACTS technology [Figures 1.

A Controller with storage is much more effective for controlling the system dynamics than the. Here also, Lngineers have to rethink the role of storage, particularly the one that can deliver or absorb large amounts of real power in short bursts.

A converter-based Controller can also be designed with so-called high pulse order or with pulse width modulation to reduce the low order harmonic generation to a very low level. A converter can in fact be designed to generate the correct waveform in order to act as an active filter.

It can also be controlled and operated in a way that it balances the unbalance voltages, involving transfer of energy between phasis. It can do all of these beneficial things simultaneously if the converter is so designed. Hingorani and Gyugyi present a practical approach to FACTS that will enable electrical engineers working in the power industry to understand the principles underlying this advanced system.

This comprehensive reference book provides an in-depth look at: 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 download 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.

Hingorani Understanding Facts

Gyugyi has published more than 50 papers in the field and holds 76 U. He is a Fellow of the IEE. Free Access. Summary PDF Request permissions.

PDF Request permissions. Tools Get online access For authors. Email or Customer ID.ISBN 1. Principle[ edit ] Typically, an SVC comprises one or more banks of fixed or switched shunt capacitors or reactors , of which at least one bank is switched by thyristors.

Hingorani and Gyugyi present a practical approach to FACTS that will enable electrical engineers working in the power industry to understand the principles underlying this advanced system.

A variety of powerful semiconductor devices not only offer the advantage of high speed and reliability of switching but, more importantly, the opportunity offered by a variety of innovative circuit concepts based on these power devices enhance the value of electric energy.

Flexible AC transmission systems. Gener- ally, this book will use the IEEE terms and definitions. Such a Controller is deflned as:

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