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Hydropower Water Head

Author: source: date: 2020-06-29 14:09:14

The difference between the upstream and downstream water levels of hydropower stations. The upstream water level minus the downstream water level is called the gross head. The gross head minus the head loss is called the net head. Head loss refers to the sum of the local head loss and the loss along the way during the process of upstream water flow from the water inlet (front tank or surge tank) through the high-pressure pipeline to the volute inlet section. Since the water levels at the upstream and downstream of the hydropower station change frequently, various combinations of the actual upstream and downstream water levels during the year will form different head values. The largest value is the largest head, and the smallest value is the smallest head. The average head can be calculated with different formulas. The simplest method is to take the arithmetic average of the maximum head and the minimum head.

关于水电站水头918 

The unit of water body per unit weight between the upstream diversion inlet section and the downstream tail water outlet section of the hydropower station

The energy difference is usually measured in meters (m). Generally expressed by the difference in water level between two sections, it is called the hydropower head of the hydropower station.

After deducting the head losses of the diversion system from the gross head, the net head of the hydropower station is obtained. Hydropower station head and reference flow are the two main dynamic factors that make up the power generation capacity of the hydropower station.

①Maximum head

That is, the maximum difference that may occur during the same period in the upstream and downstream water levels of the hydropower station. It is an important data in the design of hydropower station buildings and the strength design of hydraulic turbines.

②Minimum head

That is, the smallest difference between the upstream and downstream water levels of the hydropower station that may occur during the same period. It is the lowest water head to ensure the safe and stable operation of the water turbine under the condition of reduced efficiency of the water turbine generator.

③Average head

It is generally expressed by the arithmetic average head, and sometimes also expressed by the weighted average head of electric energy. The former is the cumulative value of the head in each period after the reservoir runoff adjustment divided by the total number of periods. The latter is to multiply the head of each period after the runoff adjustment by the output of the corresponding period, and then divide by the total output of the calculation period after accumulation. The average head of the hydropower station and the weighted average head of electric energy are used to determine various parameters of the hydroelectric generator or pump turbine, such as diameter and speed.

④Design head

China is currently designing the minimum head that can guarantee the full rated capacity of the hydroelectric generator during the operation of the hydropower station. The European and American countries call it the rated head of the hydropower station, and the Soviet Union calls it the calculated head. When the operating head of the hydropower station is less than the designed head, the output of the unit cannot reach the rated output, so it is a basic data for selecting the size of the turbine. The design head should be determined by comparative analysis. Countries in Europe and America sometimes call the head corresponding to the highest efficiency of the turbine as the design head.

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Power station classification

According to the generation head, it is divided into high-head hydropower station, middle-head hydropower station and low-head hydropower station. Countries around the world have no uniform regulations on this. China calls a power station with a water head above 70 meters a high-head power station, a power station with a water head between 70 and 30 meters is a middle-head power station, and a power station with a water head below 30 meters is a low-head power station.

Gaoshuitou Hydropower Station

Hydropower station with a water head greater than 200m. Generally, high mountain areas in the upper reaches of rivers are constructed, and most of them are diversion or hybrid hydropower stations. This kind of hydropower station often has no regulating reservoir or only a reservoir with a very low regulating capacity, so it generally does not have comprehensive utilization benefits; because the upstream and downstream water levels are relatively stable, the head changes are relatively small, and its output and power generation basically depend on the amount of incoming water . A

Zhongshuitou Hydropower Station

IMG_20170926_114521022

Comprehensive engineering facilities that convert water energy into electrical energy. It generally includes reservoirs formed by water retaining and discharge structures, water diversion systems of hydropower stations, power plants, and electromechanical equipment. The high-level water of the reservoir flows into the plant through the diversion system to push the turbine generator set to generate electrical energy, and then enters the power grid through the step-up transformer, switch station and transmission line.

Low head hydropower station

   usually refers to a hydropower station with a water head below 40m. Sometimes the hydropower station with only 2~4m water head is called extremely low head hydropower station. Most of the low-head hydropower stations are built in the middle and lower reaches of gentle slopes. They often have favorable external transportation, good construction conditions, close proximity to the power center, and easier implementation of the project. They often have channelized channels to develop shipping and diversion Benefits of irrigation. From the point of view of power generation operation characteristics, there are low runoff capacity for reservoir regulation, and most of them are runoff power plants. For example, if there is no large-scale reservoir regulation upstream, the output process changes with the change of natural flow and has poor stability.

(Part of the pictures in the article are from the Internet, no commercial marketing)

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