1、1各位老师：上午好！Lecture 12Specialized English for Electrical Engineering2Lecture 12Reading and TranslationFlexible AC Transmission SystemFACTS is defined as “alternating current transmission system incorporating power electronic-based and other static controllers to enhance controllability and increase po
2、wer transfer capability” by IEEE (Institute of Electrical and Electronics Engineers).Part 1 Concept and Development of FACTSTodays power transmission and distribution systems face increasing demands for more power, better quality with higher reliability and at lower cost as well as low environmental
3、 impact. The application of power electronics in new configurations known as FACTS (Flexible AC3Lecture 12Transmission System) offers the possibility of meeting such demands.FACTS technology uses advanced power semiconductor switching techniques to provide dynamic voltage support, power system stabi
4、lization, and enhanced power quality for transmission and distribution system application.FACTS devices are routinely employed in order to enhance the power transfer capability of the otherwise underutilized parts of the interconnected network.The use of power electronic-based apparatus at various v
5、oltage levels in electric energy systems is becoming increasingly widespread due to rapid progress in power electronic technology.The most often used power electronic elements including:i) GTO, Gate Turn-Off Thyristor.4Lecture 12ii) IGBT, Insulated Gate Bipolar Transistor.iii) IGCT, Integrated Gate
6、Commutated Thyristor.Transistor (also called Semiconductor Triode) : BJT (Bipolar Junction Transistor) which is a current controlled electronic device and FET (Field Effect Transistor) which is a voltage controlled electronic deviceBJT: Emitter, Base, CollectorFET: Source, Gate, DrainThyristor (also
7、 called Semiconductor Controlled Rectifier): Anode (positive electrode), Cathode (negative electrode), Gate5Lecture 12Part 2 Basic DC transmission systemA Static Var Compensator (SVC), according to the basic terminology established by CIGRE (International Council on Large Electric Systems), is a shu
8、nt-connected static var generator (SVG) whose output is varied so as to maintain or control specific parameters of the electric power system. The term “static” is used to indicate that SVCs, unlike synchronous compensators, have no moving or rotating main components. Thus an SVC consists of static v
9、ar generator or absorber devices and a suitable control device. Presently, in practical compensators, the generation and control of the reactive power output of a static var generator is accomplished exclusively by thyristor valves in conjunction with capacitor and/or reactor banks.6Lecture 12The ca
10、pacitor banks are either a fixed amount or are varied in steps by thyristor switching. The reactors are varied by means of thyristor switching. Based on these principles, various configuration of SVCs have been developed and applied. They are characterized by fast response, high reliability, low ope
11、rating cost and flexibility. The following types of SVCs can be identified:i) Thyristor-Controlled Reactor (TCR).ii) Thyristor-Switched Capacitor (TSC).iii) Thyristor-Controlled Transformer (TCT).iv) Self-or Line-Commutated Transformer (SCT/LCT).v) Self-of Line-Commutated Converter (SCC/LCC).7Lectur
12、e 12vii) Any Combination of above.The TCR compensator consists of a combination of thyristor-controlled reactors with fixed shunt capacitor banks. The reactors themselves also have fixed impedances but the fundamental frequency component of the current through them is controlled by thyristor valves,
13、 giving an apparently variable impedance. The branch current is controlled by phase angle control of the firing pulses to the thyristors, that is, the voltage across the reactors is the full system voltage at 90 degrees firing angle and zero at 180 degrees. The current through the reactors is the in
14、tegral of the voltage (Fig. 20.1), thus it is fully controllable with the thyristor valves between the natural value given by the reactor impedance and zero.The current in the reactor can be controlled to vary from8Lecture 12maximum to zero by controlling the firing delay angle to the thyristor valv
15、es. Hence the var output of a TCR compensator can vary continuously. TCR generates harmonics because the firing angle control results in a nonsinusoidal current waveform in the reactor. It is often necessary to remove the harmonics generated by the TCR with filters. Usually the fixed capacitor banks
16、 will be tuned to work as filters.The TSC compensator consists of one or more thyristor-switched capacitor branches. The capacitor switching (connecting) takes place at that specific instant in a cycle at which the conditions for minimum transients are satisfied, that is, when the voltage across the
17、 thyristor valve is zero or minimum. The firing delay angle control is not applicable to capacitors. A TSC branch can only provide a step change in its9Lecture 12reactive current (maximum or zero) and as a result it does not generate harmonics. Therefore a TSC compensator is a variable reactive powe
18、r source with stepwise control.Unlike mechanical switching devices such as breakers, the time between switching for the thysristor switchers in a SVC is limited only by the response time of compensator. The response time of SVCs is in the range of 2 3 cycles which makes SVCs well suited for applicat
19、ions in which fast and repetitive control of reactive power is required.In addition to the shunt-connected SVCs, there are also some alike devices in series-connection such as TCSC (Thyristor Controlled Series Compensator).The above discussion is intended as a brief summary description of static var
20、 compensators. The reader is referred to10Lecture 12some special documents for a more detailed theoretical treatment of the principle involved.1. The branch current is controlled by phase angle control of the firing pulses to the thyristors, that is, the voltage across the reactors is the full system voltage at 90 degrees firing angle and zero at 180 degrees. 通过对晶闸管点火脉冲的相角控制来控制支路电流，即，电抗器上的压降在点火角为 90度时为全部系统电压，在 180度时为零。
