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.
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.