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      水力發電機組的類型及負荷分配

      本文論述了水力發電機組的類型、特點及相應特性,同時說明了水利發電負荷分配策略和控制調節速率要求。
      關鍵詞:類型;特點;分配
              水力發電是研究將水能轉換為電能的工程建設和生產運行等技術經濟問題的科學技術。水力發電利用的水能主要是蘊藏于水體中的位能。為實現將水能轉換為電能,需要根據具體情況選取不同類型的水利發電機,并做好負荷的分配。
              1 水力發電機組的類型
              水電機組是由水輪機和發電機等組成的,發電機的響應特性比水輪機的響應特快得多,因此水電機組的響應特性主要取決于水輪機的響應特性。近代水輪機分成兩大類:反擊式和沖擊式。在轉輪內轉換成固體機械能的水流能量形式是位能、壓能和動能的水輪機,稱為反擊式水輪機。在這種水輪機中,從轉輪的進口至出口水流壓力是逐漸減小的。轉輪中的水流具有大于大氣壓的壓力,充滿全部流道。根據轉輪區域水流運動方向的特征,反擊式水輪機又分為混流式、軸流式、斜流式和貫流式等不同型式。
              2 各型水輪機的特點
              2.1 混流式水輪機?;炝魇剿啓C又叫法蘭西斯水輪機。水流沿徑向進入轉輪,然后大體沿軸向自轉輪流出?;炝魇剿啓C由于應用水頭適合多數地區的需要,以及結構簡單、運行可靠且效率高,是現代應用最廣泛的一種水輪機。在我國已建水電站中混流式水輪機采用最多。
              2.2 軸流式水輪機。軸流式水輪機轉輪區域的水流是沿軸向流動的,水流在導葉至轉輪之間轉為軸向,然后進入轉輪。根據轉輪槳葉在運行時是否可以轉動,軸流式水輪機分為軸流定漿式和軸流轉漿式兩種。軸流定漿式水輪機在運行時其轉輪漿葉固定不動,制造簡單,但它處于高效區的流量和出力范圍遠較混流式窄,當離開高效區運行時效率急劇下降。因此,這種水輪機多用于功率不大和水頭變化幅度小的水電站。軸流轉漿式水輪機在運行時其轉輪漿葉可以轉動。由于槳葉的轉動與導葉的轉動相配合,實現流量和出力的雙重調節,使其高效區的流量和出力范圍顯著擴大,并提高了它的運行穩定性。凡水頭變化大的中低水頭電站,多采用軸流轉漿式水輪機。
              2.3 斜流式水輪機。斜流式水輪機轉輪區域的水流是斜向流動的。由于轉輪葉片可以轉動而實現雙重調節,它象軸流轉槳式,處于高效率區的流量,出力范圍大。又因葉片軸線與水輪機軸線斜交,它象混流式,可比軸流式裝較多的葉片(一般為8~12片),應用水頭為30~200m。斜流式水輪機可以在比較寬的負荷范圍內穩定運行,有較高的平均效率,而其缺點卻相當突出,如結構復雜,可靠性低,容易漏油而造成污染,在吸出高度Hs=-8m條件下運行,其空蝕現象仍比較嚴重,后來把轉輪和轉輪室改為不銹鋼材料后,空蝕破壞才有所改善。由于斜流式水輪機在與混流式或軸流式水輪機的比選中無顯著特點,因此,在全國的水電設計中很少采用。
              2.4 貫流式水輪機。是一種流道呈直線狀的臥軸水輪機,其轉輪與軸流式相似,可作成定槳和轉槳兩種。貫流式水輪機的主要優點是:水流基本上沿軸向,不轉彎,提高了效率和過流能力;由于流道外形象管子且主軸臥置,可縮短機組高度、間距和簡化廠房水工結構,減少土建工程量。
              3 水力發電機組的響應特性
              水力發電機組的響應特性包括有功功率響應特性和無功功率響應特性。無功功率的調節過程無機械環節,慣性小,且調節精度指標寬。因此調節過程很快,一般無功功率突變量試驗測得均在十幾秒鐘內調節結束。有功功率的調節是通過調速器改變導葉的開度,控制水量的變化來實現的。由于水量的變化和導葉的開度并非是線性關系,而且由于引水管的長度引起水量變化的滯后效應,因此有功功率調節容易超調甚至發生振蕩,從而延長了調節過程。目前大部份水電廠已將老式的調速器更新為微機型的調速器,采用PID調節方式,調節品質大大改善。
              4 水利發電負荷分配策略
              以耗水量而言,水輪發電機組按等微增率分配有功功率是最經濟的。當機組型號和額定功率相同時,即可認為機組的水耗微增率特性是相同的,因此可簡化為水輪發電機組功率按等比例分配的原則。但是,這是忽略了水輪機的機械磨損對發電成本的影響。而水輪機的機械磨損主要是在功率調整過程中發生的。如果每次給定功率的變化,不管功率變化多大,所有參與AGC運行的機組都將進行相應的調節。例如,每八秒鐘更新一次功率給定值,也就是說在系統負荷發生變化時,每八秒鐘不管給定功率變化多大,每臺機組都要進行相應的調節,顯然這是不合理的。為此,采用“有級分配機組功率”的方法,基本上可實現每次給定功率的變化只發生在極少的機組上。所謂“有級分配機組功率”即機組的給定功率變化是階梯形的,而每一個階梯的“級差”是有限的。機組間的功率分配是有差別的,但和等微增率分配差別不大,其最大的誤差就是功率分配階梯的“級差”?!坝屑壏峙錂C組功率”相對于“平均分配機組功率”機組的調節頻度大大減少,從而減少了功率調整部件的機械磨損。當參加AGC運行的機組增加時,其優越性更加明顯。采用“有級分配機組功率”方法后,適當選擇“級差”值,每次調節只需一至二臺機組響應即可。既可大大減少機組功率調節的頻繁程度,減輕了調速器和有關部件的機械磨損,同時也滿足了經濟運行的要求。水輪發電機組的功率調節性能很好,通常機組功率從空載到滿載,負荷上升時間小于一分鐘。在有功功率控制調節下,采用PID調節方式,適當選擇PID的系數,使機組在接收到給定功率突變值后30秒內,應實現70%的功率增量的調節,并在1分鐘內完成調節過程。如果超調過大時,可采用反向的“制動”調節脈沖消除或減少超調量,從而提高了有功功率的調節品質。
              5 水利發電機控制調節速率要求
              水力發電機組的功率調節方式,可以是單機調節方式,也可以是全廠控制調節方式。兩者差別是,單機控制調節方式下,調度所給定的是每臺機組的給定功率。而全廠控制調節方式下,調度所給定的是全廠總功率,每臺機組的給定功率是由電廠計算機控制系統分配的。在每臺機組正常運行的情況下,這兩種調節方式下差別不大。但在特殊的情況下,例如在單機調節方式下,某臺機組較長時間不響應調度所給定的值,造成較大的場率調節誤差,甚至影響電能質量。而在全廠控制調節方式下可在給定功率回路中增加積分環節,彌補各機組引起的功率誤差。水輪發電機組大多采用微機型的調速器,負荷調節方便,調節范圍寬,調節速度快,可在一分鐘內從零功率增至滿負荷。為了使水輪發電機組持續穩定運行,必須設定合理的調節死區。調節死區的范圍在保證進入死區后能穩定運行的前提下,調節死區應盡可能小一些,以保證功率調節的精度,提高調節品質。一般調節死區設定為1%~2%機組功率額定值。在全廠負荷控制條件下,在功率控制回路中增加積增加積分環節,選擇合理的積分系數,能大大提高全廠總功率的調節精度。如某臺機組因故而導致和上位機通信失敗,此時積分環節能將通信失敗機組的功率差額自動轉移到通信正常的機組上,從而使全廠實發功率滿足系統的要求。
              結束語

              按照水電機組運行要求,采取不同的調節方式,可以滿足負荷分配,使全廠實發功率滿足系統的要求。

      Hydroelectric power is a science and technology that studies the technical and economic problems of engineering construction and production operation that convert water into electricity. Water used in hydroelectric power is mainly the potential energy contained in the water body. In order to realize the conversion of water to electricity, different types of water conservancy generators need to be selected according to the specific situation, and load distribution should be done.
              1 type of hydro genset
              Hydropower units are made up of turbines and generators. The response characteristics of generators are much faster than those of turbines. Therefore, the response characteristics of hydropower units depend mainly on the response characteristics of turbines. Modern turbine is divided into two categories: counterattack and impact. The hydraulic energy converted to solid mechanical energy within the rotor is in the form of a hydraulic turbine with a bit energy, a pressure energy and a kinetic energy called an impact turbine. In such a turbine, the pressure of water flow from the inlet to the outlet of the rotor is gradually reduced. The flow in the rotor has a pressure greater than atmospheric pressure, filling the entire flow path. According to the characteristics of the direction of water flow in the runner area, the impact turbine is divided into different types of mixed flow, axial flow, diagonal flow and cross flow.
              2 various types of turbine characteristics
              2.1 Francis turbine. Francis turbine Francis turbine. The water flows radially into the runner and then outflows substantially along the axial runner. Francis turbines are the most widely used turbines in modern times due to the application of water head suitable for the needs of most areas as well as the simple structure, reliable operation and high efficiency. In our hydropower station has been built in the most mixed Francis turbine.
              2.2 Axial turbine. The flow of water in the area of the runner of an axial turbine flows in the axial direction, and the flow of water flows between the guide vanes and the runner in the axial direction and then enters the runner. According to whether the runner blades can rotate during operation, the axial-flow turbine is divided into axial flow setting type and axial flow type two types. Axial flow setting turbine runner blades fixed during operation, easy to manufacture, but it is in the high-efficiency area of the flow and output range is much narrower than Francis, when leaving the high-efficiency operation of a sharp decline in efficiency. Therefore, this kind of turbine is mostly used in hydropower stations with small power and small head variation. Axial slurry turbine in the run-time can turn its blades. Due to the rotation of the blade and the rotation of the guide vane, the dual regulation of the flow rate and the output rate is realized, which greatly expands the flow rate and the output range of the high-efficiency zone and improves the running stability thereof. Where the head changes in large low-head hydropower station, use axial flow slurry turbine.
              2.3 Diagonal turbine. The flow in the area of the bevelled turbine runner is obliquely flowing. As the rotor blade can be rotated to achieve double regulation, it is like axial flow paddle, in the high-efficiency area of the flow, a large output. And because of the axis of the blade and turbine axis oblique, it is like Francis, more than the axial loading more leaves (usually 8 to 12), the application of the head is 30 ~ 200m. Diagonal flow turbines can run steadily over a wide range of load with high average efficiency, but their shortcomings are quite prominent. For example, the structure is complex, the reliability is low, the oil is easy to leak and cause pollution, and the suction height Hs = - 8m conditions, the phenomenon of cavitation erosion is still more serious, and later to the runner and runner room to stainless steel material, cavitation damage has improved. As diagonal turbines have no distinguishing features in comparison with Francis or Kaplan turbines, they are rarely used in hydropower design throughout the country.
              2.4 tubular turbine. Is a straight-flow channel is a horizontal axis turbine, the runner and axial flow similar, can be made of fixed paddle and paddle two. The main advantages of the tubular turbine are: the flow basically in the axial direction, do not bend, improve the efficiency and overcurrent capacity; as the outer tube of the flow channel and the main shaft lying on the side, can shorten the unit height, spacing and simplify the hydraulic structure of the plant, Reduce the amount of civil engineering.
              3 Hydrogenerator response characteristics
              The response characteristics of a hydroelectric generator include the active power response characteristic and the reactive power response characteristic. Reactive power regulation process without mechanical links, small inertia, and the regulation accuracy index wide. Therefore, the adjustment process is fast, the general test of reactive power abrupt changes were measured in less than ten seconds to adjust the end. Active power regulation is through the governor to change the guide vane opening, control of water changes to achieve. Because the change of water quantity and the opening of guide vanes are not linear, and due to the hysteresis effect caused by the change of water volume due to the length of the water pipe, active power regulation can easily overshoot or even oscillate, thus prolonging the adjustment process. At present, most hydropower plants have updated the old governor to a microprocessor-based governor, which adopts PID adjustment method to greatly improve the quality of adjustment.
              4 hydropower load distribution strategy
              In terms of water consumption, it is the most economical for hydro-generator units to distribute active power at equal increments. When the unit type and rated power are the same, the micro-increasing rate of water consumption of the unit can be considered as the same, so the principle that the power of the hydrogenerating unit can be equally distributed can be simplified. However, this ignores the impact of turbine mechanical wear on power generation costs. The mechanical wear and tear of the turbine occurs mainly during the power adjustment. If, for each given power change, all units involved in AGC operation will adjust accordingly, no matter how much power changes. For example, the power setpoint is updated every eight seconds, meaning that every eight seconds every eight seconds, regardless of how much a given power change, each unit must be adjusted accordingly, which obviously is not reasonable . To this end, the "step-by-step distribution of unit power" approach can be basically achieved for each given power change occurs only in very few units. The so-called "distributed power unit grade" that a unit of power change is a ladder-shaped, and each ladder "level difference" is limited. There is a difference between the power distribution among units, but the difference between them is not very different from that of other micro-increase rates. The biggest error is the "level difference" of the power distribution ladder. The power of "staged distribution unit" is greatly reduced compared to the "average distribution unit power" unit, thus reducing the mechanical wear of the power adjustment unit. When the crew to participate in AGC operation increases, its superiority is more obvious. After adopting the method of "unit power with stage distribution", the value of "level difference" should be properly selected, and only one or two units can respond to each adjustment. It can greatly reduce the frequency of unit power regulation, reduce the mechanical wear and tear on the governor and related components, and also meet the requirements of economic operation. Turbine power conditioning performance is good, usually unit power from empty to full load, load rise time of less than one minute. In the active power control regulation, the use of PID regulation, the appropriate choice of PID coefficients, so that the unit receives a given power mutation value within 30 seconds, should achieve 70% of the power increment adjustment, and completed within 1 minute Regulate the process. If the overshoot is too large, the reverse "brake" adjustment pulse can be used to eliminate or reduce the overshoot, thereby improving the adjustment quality of the active power.
              5 hydroelectric generator control regulation rate requirements
              Hydraulic power unit of power regulation, can be stand-alone regulation, also can be the whole plant control regulation. The difference between the two is that, under the control mode of single machine, the given power of each unit is given by the schedule. The entire plant control mode, the scheduling is given the total plant power, the given power of each unit is assigned by the power plant computer control system. In the case of normal operation of each unit, the two adjustment methods are not very different. However, under special circumstances, for example, in a stand-alone mode, a certain unit does not respond to a given value for a long time, causing a large error in field rate adjustment and even affecting power quality. In the whole plant control mode can be adjusted in a given power circuit to increase the integral part, make up for each unit caused by power error. Turbine generators are mostly micro-governor, load adjustment convenience, wide adjustment range, fast regulation, can be increased from zero power to full load in one minute. In order to keep the turbine unit stable and stable, a reasonable dead zone must be set. Adjust the dead zone in the premise of ensuring stable operation after entering the dead zone, adjust the dead zone should be as small as possible to ensure the accuracy of power regulation and improve regulation quality. General regulation dead zone is set to 1% ~ 2% unit power rating. In the whole plant load control conditions, the power control loop to increase the product to increase the integral part of the selection of a reasonable integral coefficient can greatly improve the plant's total power regulation accuracy. For example, if a unit fails to communicate with the host computer for some reason, the integration loop can automatically transfer the power difference of failed communication units to the normal communication unit so that the actual power of the entire plant meets the system requirements.
              Conclusion
              In accordance with the operation requirements of hydropower units, take different adjustment methods to meet the load distribution, so that the whole plant real power to meet the system requirements.



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