R. Mohan Mathur is the author of Thyristor-Based Facts Controllers for Electrical Transmission Systems ( avg rating, 12 ratings, R. Mohan Mathur's books. Engineering Books Pdf > Electrical Engineering > Electrical Engineering FACTS Controllers for Electrical Transmission Systems By R Mohan Mathur and . Thyristor Based FACTS Controllers for Electrical Transmission Systems By R Mohan Mathur and Rajiv K Varma PDF Book Download. Thyristor Based FACTS .
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R. Mohan Mathur. Ontario Power This book is printed on acid-free paper. ∞. Copyright © by the Flexible ac Transmission Systems (FACTS). FACTS pdf book itz a prescribed book in anna univ syllabus sheet for final year Mohan MathurOntario Power GenerationToronto, ON, Cana. Thyristor-Based FACTS Controllers for Electrical Transmission Systems . R. Mohan Mathur ; Rajiv K. Varma Quick Abstract | Full Text: PDF file icon PDF.
The TSC is usually tuned to a non-integer harmonic of the mains frequency so as to avoid the risk of the TSC being overloaded by harmonic currents flowing into it from the AC system. After the TSC has been switched off for a long time hours the capacitor will be fully discharged, and the thyristor valve will experience only the AC voltage of the SVC busbar. However, when the TSC turns off, it does so at zero current, corresponding to peak capacitor voltage. The capacitor only discharges very slowly, so the voltage experienced by the thyristor valve will reach a peak of more than twice the peak AC voltage, about half a cycle after blocking. The thyristor valve needs to contain enough thyristors in series to withstand this voltage safely. Deblocking — normal conditions[ edit ] When the TSC is turned on "deblocked" again, care must be taken to choose the correct instant in order to avoid creating very large oscillatory currents.
Needless to say, the era ofthe FACTS was triggered by the development of new solid-state electrical switch-ing devices. It is these systems that form the subject matter of this book.
Doing so constitutesthe increased value of transmission assets. The search for enhanced controllability of power on ac transmission networkswas initiated by newly acquired current and power controllability in HVDC trans-mission. Instead, by rapidly attaining current zero through theuse of current controllers and, in addition, by rapidly recovering the electromag-netic energy stored in the energized line, the faulted dc line could be isolated bylow interruption—rating isolators. The rapid control of power led to theadded use of HVDC links for enhancing transient stability of connected systemsthrough active-power damping.
The enhancement in stability was accomplishedby adding auxiliary signals in the current controllers of the converters , .
Thyristors offered controlled turn-on of currentsbut not their interruption. Mostapplications, however, were based on the natural commutation of currents. Inspecial cases where forced commutation was required, elaborate circuitry usingdischarging capacitors to create temporary current zeroes were employed.
Thyristors are now available in large sizes, eliminating the need for parallel-ing them for high-current applications.
Their voltage ratings have also increasedso that relatively few are required to be connected in series to yield switchesor converters for power-transmission applications.
For switching applications, such as thatfor tap changers or static phase shifters, anti-parallel—connected thyristor mod-ules, complete with snubber circuits, are available. The GTO semiconductor devices facilitate current turn-on as well as turn-off by using control signals. This technology has grown very rapidly; conse-quently, high-power GTOs are now available mm, 6 kV or mm, 9kV.
Unfortunately, the avail-able voltage ratings of these devices are still limited. Such a switch may be employed per phase to connect or disconnect ashunt-circuit element, such as a capacitor or reactor, or to short-circuit a series-connected—circuit element, such as a capacitor.
A reverse-biased thyristor auto-matically turns off at current zero, for which reason an antiparallel thyristorconnection is used to control the current through a reactor by delaying its turn-on instant, as shown in Fig.
Thus a thyristor switch offers current control in a reactor, rendering it a con-trolled reactor. However, because a capacitor current leads the applied voltageby approximately 90 , the capacitor switching always causes transient in-rush Therefore, a thyristor switch isused only to turn on or turn off a capacitor, thereby implementing a switchedcapacitor.
Parallel combination of switched capacitors and controlled reactors providesa smooth current-control range from capacitive to inductive values by switchingthe capacitor and controlling the current in the reactor.
A blockedthyristor switch connected across a series capacitor introduces the capacitor inline, whereas a fully conducting thyristor switch removes it. In reality, this stepcontrol can be smoothed by connecting an appropriately dimensioned reactorin series with the thyristor switch—as shown in Fig. A detailed discussion of this controller ispresented in Chapters 7—9. In the foregoing applications, thyristor switches were used to control thecurrent through circuit elements, such as capacitors and reactors.
The switchesare also used to perform switching actions in on-load tap changers, which maybe employed as thyristor-controlled phase-shifting transformers TCPSTs. The application of GTO devices makes forced commutationpossible, and therefore PWM converters offer a more elegant solution. The out-put voltages of PWM converters contain low-harmonic content. An alternative to a thyristor-controlled SVC is a GTO-based VSC that usescharged capacitors as the input dc source and produces a 3-phase ac voltageoutput in synchronism and in phase with the ac system.
The converter is con-nected in shunt to a bus by means of the impedance of a coupling transformer.
A control on the output voltage of this converter—lower or higher than theconnecting bus voltage—controls the reactive power drawn from or suppliedto the connected bus. This subject is dis-cussed in Chapter The use of voltage-source converters to inject a voltage by way of series-con-nected transformers leads to another interesting group of FACTS controllers: It is easy to visualize that if the reactive drop of a line is partlycompensated by an SSSC, it amounts to reducing the line reactance X L , orin other words, it is akin to controlled series compensation.
The injected voltagein the line is independent of the line current. Normally, no net energy is drawnfrom this source, but to compensate for the controller losses, the STATCOMcan operate so that it draws the compensating active power from the connectedac bus. The industries embracing these activities have been recently deregulated, and inthese sectors, competition has been introduced. For nearly years, electrical power utilities worldwide have been verti-cally integrated, combining generation, transmission, distribution, and servic-ing loads.
Also, most such utilities have operated as monopolies within theirgeographic regions. Operating the electrical energy sector competitively requires the unbundlingof generation, transmission, and distribution.
Competition is expected to existamong generators as well as retailers. The transmission and distribution i. The new order requiresnew agencies taking the responsibility to link customers loads with generators market operators and, at the same time, to clearly understand the limitationsand capabilities of power-transmission and -distribution networks , . On becoming responsible for its own business, a power-transmission com-pany must make the best use of its transmission capacity and ensure that trans-mission losses are reduced to their lowest values.
Also, any loss of transmissioncapacity means loss of income for the company; therefore, all actions must betaken to ensure that unwanted circulating power is not clogging the availabletransmission capacity. In addition, energy congestion in critical transmissioncorridors must be avoided to eliminate the risk of missed business opportuni-ties. The successof a transmission company depends on offering the maximum available trans-mission capacity ATC on its lines. The subject matter contained in this book is intended to assist engineers seek-ing FACTS knowledge and help utilities meet the energy challenge.
Adamson and N. Kimbark, Direct Current Transmission, Vol. Hingorani and L. Song and A. Johns, Eds. Litzenberger, Ed. Litzenberger and R.
Varma, Eds. Department of Energy, Portland, OR, Litzenberger, R. Varma, and J. Flanagan, Eds.
Grund et al. PAS—, No. PAS—97, No. De Doncker, O.
Demirci, S. Arthur, and V. Erinmez and A. Foss, Eds. Brochure , Paris, August To make transmission networks operatewithin desired voltage limits, methods of making up or taking away reactive-power—hereafter called reactive-power control—are discussed.
Before pro-ceeding further, however, a thorough understanding of the reactive power inac systems is necessary. Apart from the energy dissipa-tion in resistive components, all energy-coupling devices, including transform-ers and energy-conversion devices e. For the ac circuit shown in Fig. Equations 2. Equation 2. The second term has16 Written in phasor domain,the complex power in the network in Fig. Comparing Eqs.
It constitutes voltage and current loading of circuits but doesnot result in an average active power consumption and is, in fact, an impor-tant component in all ac power networks.
Figure 2. These devicesdraw lagging currents, thereby resulting in positive values of Q; therefore,they are frequently referred to as the absorbers of reactive power. These devices drawleading currents and result in a negative value of Q; thus they are seen to be sup-pliers of reactive power. The convention for assigning signs to reactive poweris different for sources and loads, for which reason readers are urged to use aconsistent notation of voltage and current, to rely on the resulting sign of Q,and to not be confused by absorbers or suppliers of reactive power.
For simplicity, the line is represented only —by its inductive reactance X l. From Fig. To keepthe voltages in the network at nearly the rated value, two control actions seempossible: Doingso causes the effective power factor of the combination to become unity. Theabsence of I x eliminates the voltage drop DV 1 , bringing V r closer in magnitudeto V s ; this condition is called load compensation.
Loads compensatedto the unity power factor reduce the line drop but do not eliminate it; they stillexperience a drop of DV 2 from j Ir X l. This compensator draws a reactive current to overcome bothcomponents of the voltage drop DV 1 and DV 2 as a consequence of the loadcurrent I l through the line reactance X l.
To compensate for DV 2 , an additionalcapacitive current, DI c , over and above I c that compensates for I x , is drawn bythe compensator. Such compensators are employed by power utilitiesto ensure the quality of supply to their customers .
In addition, these parameters depend on the bundling arrangementof the line conductors and the nearness to other parallel lines. The characteristic behavior of a transmission line is dominated by its l andc parameters.
Parameters r and g account for the transmission losses. The fun-damental equations governing the propagation of energy along a line are thefollowing wave equations: In Eqs.
It is less than thevelocity of light. From Eq. From Eqs. This substitution results in thefollowing well-recognized power equation: This transient current can take hundreds of milliseconds to die away, during which time the cumulative heating in the thyristors may be excessive. Main equipment[ edit ] A TSC normally comprises three main items of equipment: the main capacitor bank, the thyristor valve and a current-limiting reactor, which is usually air-cored.
Capacitor bank[ edit ] The largest item of equipment in a TSC, the capacitor bank, is constructed from rack-mounted outdoor capacitor units, each unit typically having a rating in the range — kilovars kVAr. The reactor is usually an air-cored reactor, similar to that of a TCR, but smaller. The size and cost of the TSC reactor is heavily influenced by the tuning frequency of the TSC, lower frequencies requiring larger reactors. The TSC reactor is usually located outside, close to the main capacitor bank.
Thyristor valve[ edit ] The thyristor valve typically consists of inverse-parallel-connected pairs of thyristors connected in series. The inverse-parallel connection is needed because most commercially available thyristors can conduct current in only one direction.
The series connection is needed because the maximum voltage rating of commercially available thyristors up to approximately 8. For some low-voltage applications, it may be possible to avoid the series-connection of thyristors; in such cases the thyristor valve is simply an inverse-parallel connection of two thyristors. The thyristor valve is usually installed in a purpose-built, ventilated building, or a modified shipping container.
Cooling for the thyristors and snubber resistors is usually provided by deionised water. This type of arrangement is useful when the power system to which the TSC is connected contains significant levels of background harmonic distortion, or where there is a risk of resonance between the power system and the TSC. In a C-type filter, the capacitor is split into two series-connected sections.