In-situ efficiency test of thermodynamic method for reversible pump turbine Huang Xiaodong (Guangzhou Storage Power Plant, Conghua 510950, Guangdong, China) currently lacks practical experience. The Guangzhou Pumped-storage Hydroelectric Power Plant (hereinafter referred to as “Guangpeng Power Plant”) has made useful attempts in this regard. After looking at the results of on-site efficiency tests for the No. 3 and No. 7 machines in the first phase of the plant, both of which are 300MWOs, The test is successful and feasible, which has accumulated valuable experience for our country to use this method in the future. Through the engineering practice of the Guangzhou Power Plant, the basic principles of the thermodynamics method, the measurement device and the analysis and evaluation of the test results were highlighted. The use of the method makes some suggestions...

The 7:1 on-site efficiency test method is of great significance for on-site efficiency testing of hydraulic units. First, the performance and quality of the hydraulic unit can be accepted on site, and the efficiency characteristics of the hydraulic unit can be identified. Second, the volute differential pressure meter can be calibrated so that the volute differential pressure meter can be used to accurately measure the flow through the hydraulic unit at any head in the future. Thirdly, it can identify other characteristics of the unit and analyze whether the vibration, cavitation, and pressure pulsation of the draft tube are related to efficiency. Fourth, provide the most reliable source data for safe and economic operation of hydropower plants.

There are many on-site efficiency test methods for hydraulic units, each with its own advantages and disadvantages. The choice of the specific method is actually the choice of flow measurement method, which mainly depends on the structure of the water head and the flow passage of the hydropower plant. The current internationally recognized methods for efficiency testing of large and medium-sized hydropower plants are: flow meter method, water hammer method, tracer method, volute differential pressure method, relative method, ultrasonic method, and thermodynamic method for directly measuring the unit efficiency. Among them, the flow meter method is relatively primitive, and it is a feasible but unsatisfactory method; the water hammer method is suitable for power plants with medium and high heads, and the water diversion system is a closed pipe with equal diameter or contraction shape, and the straight section with equal diameter should meet 50m2/s. Trace test cost is high, and the test process is complicated. The volute pressure difference method is simple and can be monitored in real time. However, other methods with higher precision are required to determine the volute pressure coefficient of the volute; the relative method has a wide range of applications and low cost, but the measurement accuracy is low. Absolute flow rate and absolute efficiency value cannot be measured. Ultrasonic method requires uniform distribution of flow velocity at the cross section. It must have an exposed flat tube length of 2D (pressure line diameter) or more. Different channels have different straight length requirements. The instrument is expensive; the thermodynamics law only requires that the power head be higher than 150m, and the higher the head, the higher the measurement accuracy. At the same time, a one-hole four-machine program is used. The working conditions are numerous and the flow state is relatively complex. From the perspectives of accuracy, economy, convenience, and operability, the thermodynamic method is used for on-site operations. Rate test is the best choice. The first phase of the Guangzhou Power Plant (4X300MWO pump turbine was supplied by the Neyrpic plant in France, and the second phase (4X300MWO) was supplied by the German VOITH plant. In response to the owner’s request, the first phase of the project was conducted in August 1994 on site machine 3 for efficiency testing. The second phase of the project was tested on April 7 in April 2000. The tests were carried out by the French company NEY RPIC and the German VOITH plant, under the supervision of the consultant company Lahmeyer and the owner’s representative. The time, the different units, and the same method have all been successful, and this is where our field power efficiency tests for turbines (especially reversible pump turbines) are lacking practical experience in China today. This made a useful attempt, which undoubtedly contributes to the promotion and application of this law in China in the future.

2 The basic principle of the thermodynamic determination The thermodynamic measurement of turbine efficiency was first proposed by Frenchman Poirson in 1914. He believes that the hydraulic loss generated in the turbine is completely converted to heat energy, so that the temperature of the water flowing through the turbine rises. Therefore, the water temperature difference between the inlet and outlet of the turbine can be measured to determine the efficiency of the turbine. The basic basis of this method is the law of conservation of energy.

Under actual operating conditions, the energy delivered by the unit mass of water flowing through the unit to the main shaft of the turbine or the energy obtained from the pump shaft depends on the measurements of the inlet and outlet characteristic variables (pressure p, temperature v, flow V, and water level z) of the unit. The thermodynamic properties of water, said this part of the energy for the unit mass mechanical energy Em.Em expression: P1, P2 for the unit inlet and outlet section pressure; 1, V2 for the unit inlet and outlet section flow velocity; for the acceleration of gravity, m / S2;1, Z2 is the elevation of the inlet and outlet sections of the unit, m; 茁 is the energy correction factor.

Under ideal operating conditions, that is, friction-free flow, the energy delivered by a unit of mass of water to or from the shaft of the turbine depends only on the nature of the water and the characteristics of the hydropower plant. This energy is called the unit mass of water Eh. See equations (1) and (2) to obtain the hydraulic efficiency of the unit without measuring the flow rate. See Tables (3) and (4).

In practical applications, the measurement of the quantity of mechanical energy per unit mass is performed by means of a measuring vessel connected to the inlet and outlet measuring sections of the unit (see). The expression of the mechanical energy per unit mass changes to: The pressure in the measuring vessel at the high and low pressure side ,Pa;11,z21 is the center elevation of the high-low pressure side measurement container, mmvn, V21 is the water flow rate in the high and low pressure side measurement vessels where: vn=Qn/V21=Q21/.(Qn, Q21 is the flow height, The flow rate of the low-pressure side measurement vessel, m3/s; 1, S2, is the cross-sectional area of ​​the high- and low-pressure side measurement vessels. m2) In order to improve the measurement accuracy of the unit mass mechanical energy, the thermodynamic method is generally used to determine the device. Efficiency test In accordance with IEC as an example, the thermodynamic measurement device is described (see). The high-pressure side measurement device of the Guangzhou Power Plant is located in the middle of the expansion joint between the volute inlet and the inlet ball valve. The two sampling points (DS) are symmetrical. The distribution is located in the horizontal plane through the diameter.

The water sample taken from the sampling point DS is entered into the high pressure expander HE through the manual valve BK and the throttle valve VD. The water pressure Pu after expansion is measured by the pressure sensor DM. The wear power is obtained through actual measurement; P is the unit shaft power turbine Operating conditions: P=Pgn+PLn Water pump operating conditions: P=Pm (t-PLmot (where Pg (1Pmo is the input and output power of the generator or motor, respectively, measured by the three-phase power meter; PLgen and PW are The mechanical loss of the generator or motor is obtained by measurement).

The temperature sensor TH is connected to the measuring bridge MB. The water sample taken out is introduced into the test table via the pipeline and connected to the flowmeter D through the regulating valve HD. The flow rate of the sample Q11 is measured by the flowmeter D to calculate the flow rate of the water in the expander V1U. The water temperature of the tank AB is measured by the thermometer Twd. Measured, the accuracy of the thermometer is 1/100 °C. The low-pressure side measurement section is located at the outlet of the draft tube, there are three sampling points (SS), the middle position of the two sides and the top of the layout of each one, the actual use of only two sides The middle position of 2 measuring points. The water sample from the sampling point SS is collected in the adiabatic pipe (stainless steel pipe buried in concrete) and is connected to the helium pipe and the pressure sensor DM. The measured cross-sectional areas A1 and A2 of the inlet and outlet measuring sections of the combined assembly can be obtained. Average flow rates V1 and V2 through the two sections Huang Xiaodong: On-site efficiency test of the thermodynamic method of the reversible pump turbine The thermistor TH is installed in the TE expansion tank. The thermistor TH is connected to the measurement bridge MB.

The difference in water temperature between the high and low pressure sides is measured by the "single measuring bridge" MB with amplifier. The thermistor TH (standard resistance at 31°C at 25°C) is equipped with a 3-wire connection cable to counteract the effect of the cable resistance on the measurement. In order to observe the fluctuation of water temperature, water is drawn to the water tank in the section of the tail water conical tube (measuring point 39), and the temperature of the water is continuously measured and recorded using a resistance-type temperature sensor Tws and a recorder PL.

4 Analysis of test results and evaluation The main results of No. 3 pump turbine on-site efficiency tests are given in the main results of No. 7 pump turbine field performance tests.

Only when it is confirmed that the test is successful and the result is credible, can it be calculated according to IEC 80%; The integrated error of the water turbine working condition is ± 0,87 %, and the comprehensive error of the pump working condition is ± 1 08% ~ ± 177%; the international regulation considers that the integrated error should not exceed ± 15% ~ ± 25%. Proof test from the error size point of view The results are acceptable.

42 The linear relationship between the square root of the pressure difference between the flow and the volute is deduced from the theory: Q=K indicates that the relationship between the flow Q passing through the unit and the square root of the volute differential pressure should be linear. Therefore, this can be used as one of the criteria for verifying the success of the test.

Taking Unit 3 as an example, in the efficiency test, the relation between K and Q is obtained (see). It can be seen from this that the value of K is basically close to the constant 2588, and the error is about 24. The volute differential pressure coefficient of the 3 Whether the characteristic curve is consistent or not According to the data obtained from the test, the relationship curve between unit output and efficiency, flow rate, water head, etc. is plotted. If these relationships are smooth and smooth, the trend of change conforms to the general law, then the test is successful and the result is credible. of.

From the test results,3 we can see that the values ​​and trends of the output curves/input and efficiency of the unit, the flow rate, the head/head curve, etc. do indeed conform to the general logic and are consistent.

To sum up, the use of thermodynamics for the Guangzhou Power Plant to perform field tests on the efficiency of the reversible pump turbine is successful and the results are credible. The weighted average efficiency of the measured turbine operating conditions for the first phase of the No. 3 turbine is 905%, and the guaranteed value is 9068%. Considering the comprehensive error of ±08%, the results are still acceptable; the measured weighted average efficiency of the pump operating conditions is 9250%. Greater than the guaranteed value of 9231%. The second phase of the 7th machine was measured as: the turbine weighted average efficiency of 92 69%, greater than the guaranteed value of 9242%; pump operating conditions in the range of 528 ~ 537m head, the efficiency of the head and the relationship is not, For this reason, it is best to compare the average value, in the range of 528~534m for the lift, the average efficiency of the pump operating conditions is 93.34%, which is greater than the guaranteed value of the head range of 93.12%. From the results of the first and second phase site efficiency test. It can be seen that the second-phase pump turbine has a relatively wide high-efficiency zone to achieve higher weighted average efficiency.

44 The problems that should be paid attention to when increasing the measurement accuracy In order to improve the measurement accuracy, in addition to requiring the instrument and equipment to have sufficient accuracy and correct operation methods, the following problems should also be noted: (1) Head. The head should be above 150m. Because the higher the head, the greater the water temperature difference between the inlet and outlet of the turbine, the higher the measurement accuracy. With the continuous improvement of measuring instruments and measurement methods, the scope of application of this method can also be extended to the power plant with a head of more than 100m.

judgment. Whether the test results are credible or not should be specifically analyzed from the following aspects. (2) The pipelines buried in the mixed soil under adiabatic conditions (continued on page 66) Speed ​​governor Pressure tank Automatic replenishment Gas tank High pressure alarm signal, when the pressure is less than 65 MPa, a low pressure alarm signal is issued; each tank is on The set value of the safety valve is filled with water through two 4m3 pressurized water storage tanks for each unit to pressurize the draft tube. When the water level of the draft tube reaches the height of 202 95m, the inflation is stopped.

During the phased operation, in order to maintain the water level of the draft tube not to rise due to the leakage of the compressed air, compressed air can be automatically supplied to the draft tube through the water level switch and the solenoid valve.

As the possible leakage of the hydraulic circuit of the governor system causes the pressure of the pressure tank to decrease and the oil level rises, when the pressure tank reaches the high oil level, the float switch acts to automatically replenish the pressure to the pressure tank; when the oil level reaches the rated value , End of qi. It is also possible to manually replenish the pressure tank of the governor system. 5 Low-pressure gas system The low-pressure gas system is composed of maintenance gas system and brake gas system. It is used in power plants (factory building, main transformer hole, tail water accident gate room). Routine maintenance requires compressed air and unit braking. Daily maintenance needs compressed air production volume of 180m3/h. Air consumption during braking is 401/set. System pressure is 0. Unit brake gas system has 2 air-cooled air compressors of the same type and 1 Gas storage tanks, air compressor displacement of 1.64m3/min exhaust pressure of 0 8MPa which one for the main, one standby, can switch each other storage tank volume of 4m3, to provide brake gas for each unit. The gas tank is provided with a pressure switch. When the measured pressure value is less than 06MPa, the air compressor is started. If the pressure value is greater than 0 MPa, it is stopped; when the pressure value is greater than 1.0MPa, a high pressure alarm signal is issued; when the pressure value is less than 0 . 55MPa sends out the low pressure alarm signal, and at the same time overhauls the gas supply to the brake system; when the pressure is greater than 1.1MPa, the safety valve on the gas tank opens.

The overhaul gas system is equipped with a set of air compressors, with a discharge capacity of 3.2 m/min and a discharge pressure of 0.8 MPa. The air compressor outlet is connected to a 4m3 vertical gas tank with an access hole and safety valve. , Pressure gauges, pressure switches for controlling the start and stop of air compressors, undervoltage switches, overpressure switches, and solenoid valves for automatic blowdown. Compressed air is distributed from the 4m3 gas storage tank through pipelines to each floor of the plant, the main transformer hole and the tail water accident gate room, and each site is provided with a number of joints. When the pressure value measured by the pressure switch on the gas tank is less than 06MPa, the air compressor is started. When the pressure value is greater than 09MPa, the air compressor stops; when the pressure value is greater than 10MPa, a high pressure alarm signal is issued; when the pressure value is less than 0.55 In case of MPa, a low pressure alarm signal is issued; when the pressure is greater than 1. 1 MPa, the safety valve on the gas tank is opened. The brake system can also supply gas for maintenance.

The brake gas system and the overhaul gas system are used as backups. They can be operated in the following ways: 1 Normal operation; 21 air compressors for brake maintenance; 3 Air compressors for inspection and repair; 4 Maintenance gas storage Gas tank maintenance; 5 brake gas tank maintenance.

The main shaft maintenance and sealing gas is taken from the high pressure gas system and the pressure is reduced to 1.2 MPa after a pressure reducing valve to supply the gas to the main shaft seal. In order to ensure the reliability of the seal, a 150L gas storage tank is specially provided to make up for the loss of the gas leakage from the piping system. Each unit is equipped with a pressure switch to prevent the unit from starting up inadvertently when the maintenance seal is still under pressure.

(Continued from page 63.) The thermal conditions are good, but the pipes exposed to the atmosphere must be properly corrected due to the insulation measures and the heat exchange with the outside world. .

(3) Stable conditions. For the same measuring point, the following stable conditions shall be satisfied: The power change of the generator motor shall be within 1.5% of the average value; the change of the unit mass of water energy shall be less than 1% of the average value; and the rotation speed of the unit shall not exceed 0.5 of the average value. %(4) Avoid interference. If there are multiple units in the power plant, especially in the case of “one hole with multiple machines”, it is best to suspend the use of other units (especially adjacent units) during the test, otherwise it will affect the test accuracy and results.

(5) Avoid the cavitation area. Since cavitation occurs, water vaporization absorbs heat from the surroundings, causing additional water temperature changes, which affects the measurement accuracy.

(6) Other factors. For example, the unit cooling water intake and drainage, if possible, should be taken from other units as far as possible and discharged to other places, so as not to affect the test results; if the spindle seal cooling can not be taken effective measures should be corrected; for the need to air the unit, in the test The replenishment should be stopped during the process (because replenishment brings outside heat into the water) so as not to affect the measurement results.

5 Conclusions (1) For high head water reversible pump turbines, whether it is the turbine working conditions or the pump operating conditions, it is feasible to use the thermodynamic method to conduct on-site efficiency tests. (2) The efficiency test does not need to measure the flow, so the workload is not large, only 3 For 5 people, the calculation is also very simple. The efficiency value can be calculated after the end of the test.

(3) The test results can be used to determine the volute differential pressure coefficient, so that on-line monitoring of unit flow and efficiency can be performed in the future.

(5) In view of the many advantages of the thermodynamic method, it is recommended that this method be used as far as possible for hydropower plants with test conditions, and that satisfactory technical and economic results will be achieved.

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