電氣工程及其自動化 外文翻譯 外文文獻(xiàn) 英文文獻(xiàn) 電力系統(tǒng)的簡介

Brief Introduction to The Electric Power System Part 1 Minimum electric power systemA minimum electric power system is shown in Fig.1-1, the system consists of an energy source, a prime mover, a generator, and a load. The energy source may be coal, gas, or oil burned in a furnace to heat water and generate steam in a boiler; it may be fissionable material which, in a nuclear reactor, will heat water to produce steam; it may be water in a pond at an elevation above the generating station; or it may be oil or gas burned in an internal combustion engine. The prime mover may be a steam-driven turbine, a hydraulic turbine or water wheel, or an internal combustion engine. Each one of these prime movers has the ability to convert energy in the form of heat, falling water, or fuel into rotation of a shaft, which in turn will drive the generator.The electrical load on the generator may be lights, motors, heaters, or other devices, alone or in combination. Probably the load will vary from minute to minute as different demands occur.The control system functions （are） to keep the speed of the machines substantially constant and the voltage within prescribed limits, even though the load may change. To meet these load conditions, it is necessary for fuel input to change, for the prime mover input to vary, and for torque on the shaft from the prime mover to change in order that the generator may be kept at constant speed. In addition, the field current to the generator must be adjusted to maintain constant output voltage. The control system may include a man stationed in the power plant who watches a set of meters on the generator output terminals and makes the necessary adjustments manually. In a modern station, the control system is a servomechanism that senses generator-output conditions and automatically makes the necessary changes in energy input and field current to hold the electrical output within certain specifications.Part 2 More Complicated SystemsIn most situations the load is not directly connected to the generator terminals. More commonly the load is some distance from the generator, requiring a power line connecting them. It is desirable to keep the electric power supply at the load within specifications. However, the controls are near the generator, which may be in another building, perhaps several miles away.If the distance from the generator to the load is considerable, it may be desirable to install transformers at the generator and at the load end, and to transmit the power over a high-voltage line (Fig.1-2). For the same power, the higher-voltage line carries less current, has lower losses for the same wire size, and provides more stable voltage.In some cases an overhead line may be unacceptable. Instead it may be advantageous to use an underground cable. With the power systems talked above, the power supply to the load must be interrupted if, for any reason, any component of the system must be moved from service for maintenance or repair. Additional system load may require more power than the generator can supply. Another generator with its associated transformers and high-voltage line might be added.It can be shown that there are some advantages in making ties between the generators (1) and at the end of the high-voltage lines (2 and 3), as shown in Fig.1-3. This system will operate satisfactorily as long as no trouble develops or no equipment needs to be taken out of service.The above system may be vastly improved by the introduction of circuit breakers, which may be opened and closed as needed. Circuit breakers added to the system, Fig.1-4, permit selected piece of equipment to switch out of service without disturbing the remainder of system. With this arrangement any element of the system may be deenergized for maintenance or repair by operation of circuit breakers. Of course, if any piece of equipment is taken out of service, then the total load must be carried by the remaining equipment. Attention must be given to avoid overloads during such circumstances. If possible, outages of equipment are scheduled at times when load requirements are below normal. Fig.1-5 shows a system in which three generators and three loads are tied together by three transmission lines. No circuit breakers are shown in this diagram, although many would be required in such a system. Part 3 Typical System LayoutThe generators, lines, and other equipment which form an electric system are arranged depending on the manner in which load grows in the area and may be rearranged from time to time. However, there are certain plans into which a particular system design may be classified. Three types are illustrated: the radial system, the loop system, and the network system. All of these are shown without the necessary circuit breakers. In each of these systems, a single generator serves four loads.The radial system is shown in Fig.1-6. Here the lines form a “tree” spreading out from the generator. Opening any line results in interruption of power to one or more of the loads.The loop system is illustrated in Fig.1-7. With this arrangement all loads may be served even though one line section is removed from service. In some instances during normal operation, the loop may be open at some point, such as A. In case a line section is to be taken out, the loop is first closed at A and then the line section removed. In this manner no service interruptions occur.Fig.1-8 shows the same loads being served by a network. With this arrangement each load has two or more circuits over which it is fed.Distribution circuits are commonly designed so that they may be classified as radial or loop circuits. The high-voltage transmission lines of most power systems are arranged as network. The interconnection of major power system results in networks made up by many line sections. Part 4 Auxiliary EquipmentCircuit breakers are necessary to deenergize equipment either for normal operation or on the occurrence of short circuits. Circuit breakers must be designed to carry normal-load currents continuously, to withstand the extremely high currents that occur during faults, and to separate contacts and clear a circuit in the presence of fault. Circuit breakers are rated in terms of these duties. When a circuit breaker opens to deenergize a piece of equipment, one side of the circuit breaker usually remains energized, as it is connected to operating equipment. Since it is sometimes necessary to work on the circuit breaker itself, it is also necessary to have means by which the circuit breaker may be completely disconnected from other energized equipment. For this purpose disconnect switches are placed in series with the circuit breakers. By opening these disconnectors, the circuit breaker may be completely deenergized, permitting work to be carried on in safety.Various instruments are necessary to monitor the operation of the electric power system. Usually each generator, each transformer bank, and each line has its own set of instruments, frequently consisting of voltmeters, ammeters, wattmeters, and varmeters.When a fault occurs on a system, conditions on the system undergo a sudden change. Voltages usually drop and currents increase. These changes are most noticeable in the immediate vicinity of fault. On-line analog computers, commonly called relays, monitor these changes of conditions, make a determination of which breaker should be opened to clear the fault, and energize the trip circuits of those appropriate breakers. With modern equipment, the relay action and breaker opening causes removal of fault within three or four cycles after its initiation. The instruments that show circuit conditions and the relays that protect the circuits are not mounted directly on the power lines but are placed on switchboards in a control house. Instrument transformers are installed on the high-voltage equipment, by means of which it is possible to pass on to the meters and relays representative samples of the conditions on the operating equipment. The primary of a potential transformer is connected directly to the high-voltage equipment. The secondary provides for the instruments and relays a voltage which is a constant fraction of voltage on the operating equipment and is in phase with it；similarly, a current transformer is connected with its primary in the high-current circuit. The secondary winding provides a current that is a known fraction of the power-equipment current and is in phase with it. Bushing potential devices and capacitor potential devices serve the same purpose as potential transformers but usually with less accuracy in regard to ratio and phase angle.中文翻譯：電力系統(tǒng)的簡介第一部分：最小電力系統(tǒng) 一個最小電力系統(tǒng)如圖1-1所示，系統(tǒng)包含動力源，原動機(jī)，發(fā)電機(jī)和負(fù)載。 動力源可能是火爐中的煤，燃?xì)饣蚴?，加熱鍋爐中的水而產(chǎn)生蒸汽。它也可能是可裂變的材料，如原子核反應(yīng)堆，加熱水而產(chǎn)生蒸汽；也可能是在高海拔發(fā)電站上水池的水；或者是石油或燃?xì)庠趦?nèi)燃機(jī)中的燃燒。 原動機(jī)可能是汽輪機(jī)，水輪機(jī)，水車，或內(nèi)燃機(jī)。這些原動機(jī)中的一種都有能力把其他形式的能量轉(zhuǎn)化為熱能，勢能，或使軸轉(zhuǎn)動的能量，進(jìn)而驅(qū)動發(fā)電機(jī)工作。發(fā)電機(jī)上的電負(fù)載可能是燈，電動機(jī)，加熱器或是其他設(shè)備的個體或組合。負(fù)載可能在每一分鐘內(nèi)都會產(chǎn)生不相同的需要?？刂葡到y(tǒng)的功能是保持機(jī)器的速度是個穩(wěn)定值和保持電壓在規(guī)定的范圍內(nèi)變化，即使負(fù)載可能發(fā)生變化。要滿足這些負(fù)載的條件，需要燃料輸入的變化，需要原動機(jī)輸入的變化，這是為了改變發(fā)電機(jī)中原動機(jī)軸的轉(zhuǎn)矩保持恒定。此外，發(fā)電機(jī)的勵磁電流必須加以調(diào)整，以保持恒定電壓輸出。該控制系統(tǒng)可能包括一個駐扎在電廠里的人，他看管著發(fā)電機(jī)輸出終端的一整套儀表和有時進(jìn)行必要的手動調(diào)整。在一個現(xiàn)代化的電站里，控制系統(tǒng)用來感應(yīng)發(fā)電機(jī)輸出條件，在能源輸入中自動進(jìn)行必要的改變和磁場電流在規(guī)定的范圍內(nèi)保持電力輸出的一個伺服機(jī)構(gòu)。第二部分：更復(fù)雜的系統(tǒng)在大多數(shù)情況下負(fù)載不是直接與發(fā)電機(jī)終端連接在一起的。更常見的是負(fù)載與發(fā)電機(jī)有一段距離，需要電源線把它們連接起來。理想情況下是在規(guī)定的范圍內(nèi)對負(fù)載保持電能補(bǔ)給，進(jìn)而控制附近的發(fā)電機(jī)。發(fā)電機(jī)可能在另一幢大樓里，也可能有幾英里遠(yuǎn)。如果發(fā)電機(jī)到負(fù)載的距離是合理的，理想的情況是在發(fā)電機(jī)和負(fù)載的端部都安裝變壓器，通過高壓線路傳送電能（如圖1-2）。 對于相同的電能輸送，更高的電壓線路會流過更小的電流，對于同樣尺寸的電線則降低更多的損耗，提供更穩(wěn)定的電壓。 在某些情況下架空線可能是不合適的。相反，使用地下電纜可能會更有利。上面談到的電力系統(tǒng)，不管任何原因，負(fù)載的電能補(bǔ)給必須被中斷，供電中系統(tǒng)的任何元件必須被維護(hù)或者被移除。其他系統(tǒng)的負(fù)載所需的電能可能比發(fā)電機(jī)需要的電能更大。另外，與發(fā)電機(jī)相關(guān)的變壓器和高壓線路可能被增加。由上可以說明連接發(fā)電機(jī)（1）和高壓線路末端（2和3）是有一些優(yōu)勢的，如圖1-3所示。這個系統(tǒng)只要沒有任何故障或沒有需求的設(shè)備在供電中被移除時，其運(yùn)行將令人滿意。上面的系統(tǒng)通過引進(jìn)斷路器將有很大的改善，這需要使用斷路器的開通和關(guān)斷功能。增加斷路器的系統(tǒng)，如圖1-4，允許選擇某臺設(shè)備在供電中被關(guān)斷，不會影響剩余的系統(tǒng)設(shè)備。采用這種布局的系統(tǒng)可能通過斷路器的操作對其進(jìn)行不帶電的維護(hù)或維修。當(dāng)然，任何一臺設(shè)備從供電中被移除，總負(fù)載必須在剩余設(shè)備中被運(yùn)行。在上述情況下必須注意的是避免過載。如果可能，在低于正常值的負(fù)載需求，設(shè)備的停電是要有時間計劃的。如圖1-5所示，通過三條輸電線路，系統(tǒng)的三個發(fā)電機(jī)和三個負(fù)載是捆綁在一起的。在此圖中沒有斷路器，然而在很多時候這樣的系統(tǒng)是被需要的。第三部分:典型的系統(tǒng)布局電力系統(tǒng)中發(fā)電機(jī)，線路和其他設(shè)備根據(jù)該地區(qū)負(fù)載的增加和變化不時的被重新排放。然而，真正的計劃歸類是一個特別的系統(tǒng)設(shè)計。三種系統(tǒng)類型說明：放射性系統(tǒng)，循環(huán)系統(tǒng)和網(wǎng)絡(luò)系統(tǒng)。所有這些都說明不需要斷路器。這些系統(tǒng)中的每一個都是由一個發(fā)電機(jī)來供給四個負(fù)載。放射性系統(tǒng)如圖1-6所示。這些線路形成一棵樹的形狀，從發(fā)電機(jī)蔓延出去。開通任何線路可能會導(dǎo)致一個或多個負(fù)載電源的中斷。如圖1-7循環(huán)系統(tǒng)的圖解。這樣的排列能給所有負(fù)載供電，即使線路中的一部分在輸電過程中被移除。在某些正常操作情況下，循環(huán)中的某些點可能被打開。例如A點，部分線路被移除，循環(huán)在A點處首先被關(guān)閉，然后線路節(jié)點被移除。這種方式是不會發(fā)生供電中斷的。如圖1-8所示通過網(wǎng)絡(luò)對相同負(fù)載供電。在這樣的排列下，每個負(fù)載的供電將通過兩條或更多的線路來完成。配電線路有共同的設(shè)計方案，以便它們能作為放射型或循環(huán)型線路而被分類。大多數(shù)高壓傳輸線路作為網(wǎng)絡(luò)型系統(tǒng)被排放。主要電力系統(tǒng)互相連接，是通過許多線路而組成網(wǎng)絡(luò)。第四部分：輔助設(shè)備在正常運(yùn)行或發(fā)生短路時，斷路器是必要的斷電設(shè)備。斷路器的設(shè)計必須不斷地承受正常負(fù)載，承受超高電流，這是為了在發(fā)生故障期間，斷開連接和清除這條線路的故障。斷路器根據(jù)其職責(zé)來設(shè)定額定值。當(dāng)斷路器斷開，切斷一臺設(shè)備的電源時，斷路器的一側(cè)通常保持通電，因為它是連接在運(yùn)行中的設(shè)備。由于它有時需要對其本身進(jìn)行操作，也需要通過對斷路器與帶電設(shè)備進(jìn)行完全隔離的手段。為此，隔離開關(guān)被放置與斷路器串聯(lián)。通過斷開這些隔離開關(guān)，斷路器可完全切斷電源，使工作安全進(jìn)行。使用各種儀表去監(jiān)視電力系統(tǒng)的運(yùn)行是必要的。一般每一個發(fā)電機(jī)，每一個變壓器組，每一條線路都有它自己的整套儀表，通常包括：電壓表，電流表，有功功率表和無功功率表。當(dāng)系統(tǒng)發(fā)生故障時，在這種條件下系統(tǒng)要經(jīng)受一個突然的改變。電壓通常下降，電流上升。這些改變最明顯的是緊鄰的故障。在線模擬計算機(jī)，通常稱為繼電監(jiān)視器，去監(jiān)視這些情況下的改變。斷路器的斷開，有效得清除故障和帶電的跳閘回路。隨著現(xiàn)代化設(shè)備的發(fā)展，故障發(fā)生后，繼電器的動作和斷路器的開啟在三個或四個周期內(nèi)可將故障移除。儀表可顯示電路情況和保護(hù)電路的繼電器有沒有直接安置在電源線上，但是儀表被放置在控制房里的開關(guān)屏上。儀表互感器被安裝在高電壓設(shè)備上，意味著它可以在設(shè)備運(yùn)行的條件下傳遞儀表和繼電器的典型信號。電壓互感器的原邊直接連接著高壓設(shè)備。副邊在運(yùn)行的設(shè)備上，為儀表和繼電器電壓提供一個恒定的電壓分?jǐn)?shù)和電壓相位。同樣地，電流互感器連接著高壓回路的原邊。副邊繞組提供一個已知的電源設(shè)備分?jǐn)?shù)和與之同相的電流。潛在的襯套設(shè)備和潛在的電容器設(shè)備服務(wù)于相同的目的，視為潛在的變壓器，但通常就變比和相角而論，精確性更低。 10