Identification of main dynamic characteristic parameters of steam turbine generator set based on dynamometer load rejection test

The dynamometer load test is an artificially triggered steam turbine overspeed protection system in the case where the unit is not disassembled, so that the steam turbine inlet valve is suddenly closed, and the subsequent generator active power change process is measured, according to which the conversion is under the equivalent condition. The imaginary "the highest load-lifting speed of the conventional load shedding, and the unit does not actually overspeed, so it has the advantages of safety, simplicity, and economy. In recent years, China has carried out many fruitful researches on improving the accuracy of the dynamometer load test. Work>4, recently proposed a high-precision algorithm for converting the whole speed of the fly-up process. These research results have laid a foundation for the popularization and application of the dynamometer load-shedding test method. The change of the basic unit load-shedding test conditions is severe enough to stimulate the main dynamics of the system. In response to this, this paper combines the existing research results of the turbo-generator system model, and proposes the key measurement data that can be provided by the dynamometer load-shedding test, and identifies the steam turbine generator set identified by the main dynamic characteristics of the steam turbine generator set. The dynamic characteristic parameters can be used for dynamic characteristics analysis such as the speed flying process. Improving the technical level and economic benefit of the dynamometer load test has practical significance. 1 Using the dynamometer load test to identify the main dynamic characteristics of the steam turbine generator. 1.1 dynamometer load test model parameter analysis dynamometer load test When the unit is connected to the grid, the mathematical model describing the process includes the cylinder volume of the turbine rotor and the generator. Some of the more mature models are available for the quenching test of a steam turbine generator set. The mathematical model takes into account the nonlinear link of the generator power angle characteristics.

PC* commands such as high-pressure cylinder Ph medium and low-pressure cylinder motor model 级 section pressure, steam power, electric power, speed; if it is the standard network frequency; 6 is the generator power angle (with dimension); is h, respectively, high, The medium pressure oil motive time constant; respectively, the volume time constant of the high pressure to and medium and low pressure cylinders, respectively called the high power te and the medium and low pressure cylinder power coefficient; ra is the rotor time constant; is the damping torque coefficient.

The mathematical model of the dynamometer load test can be seen that the steam turbine generator set belongs to a kind of “gray box” system, and some of its dynamic characteristic parameters can be obtained by parameter estimation method. The specific analysis is as follows: at a certain acceleration power (steam power and Under the difference of electric power, the rotor time constant Ta is the determinant of the speed fluctuation process. One of the basic conditions of the dynamometer test method is that the rotor time constant TaTa can be calculated according to the design, or it can be the same or the same type. The unit's first routine load rejection test was measured, so it is believed that Ta is known in this study.

The time constant T* and "characterizes the response speed of the high and medium pressure oil motives to the OPC command. It is related to how much steam enters the steam turbine after the OPC command is issued. After the load rejection of the unit, 2001i27; repaired 2001r0al*leeepublish speed The flying process has a direct influence on the input of high-pressure medium-pressure oil motives. 33. Development and development. Yu Daren et al. Identification of main dynamic characteristics of steam turbine generators based on dynamometer load rejection test (OPC command) and output ( The high and medium pressure valve opening degrees are all measurable parameters. According to this, the time constants Tsh and Tm can be identified, and the identification process can be carried out independently, which is relatively easy, so it is not the focus of this paper.

High-medium-low pressure cylinder volume time constant 7, "Cylinder volume is an energy storage link. Even if the steam valve can be completely shut down immediately during normal load rejection, the steam stored in the cylinder volume will continue to work, causing the unit to generate overspeed with the large capacity of the unit. The rotor time constant has a tendency to decrease. In addition, the oil engine closing speed is also increased. Therefore, the specific gravity of the cylinder volume time constant affects the speed flying process is relatively strong.

Due to the complexity of the steam turbine structure, it is difficult and inaccurate to calculate the cylinder volume time constant through design calculation. At present, each cylinder is equivalent to a concentrated volume, and its volume time constant is determined by the conventional load rejection test in the model shown. The steam turbine is equivalent to two concentrated volumes of high pressure cylinder and medium and low pressure cylinder, which can more accurately describe the dynamic characteristics of the turbine. The cylinder volume time constant and 7 are two important parameters to be identified. They analyze the dynamics of the turbine and the regulation system. The characteristic has the practical sense of the damping torque coefficient Cd and the initial power angle of the generator. When the load rejection method of the steam turbine generator set is used, the intake steam generated during the valve closing process and the shaft power generated by the cylinder volume storage are used to work on the grid. The electromagnetic torque is mainly composed of the synchronous torque of the power angle W phase and the damping torque (asynchronous torque) in phase with the speed difference (k - k). The dynamic behavior of the generator is the strength of the damping torque. Especially, the process of low-frequency oscillation, asynchronous operation and resynchronization has a significant influence on the calculation formula of Cd, but the form is more complicated and involves the shadow. Considering that the dynamometer load test can fully stimulate the dynamic response of the generator, if the Cd is identified by the test measurement data, it will have practical significance. In addition, since the synchronous torque is a nonlinear function of the power angle W, the analysis of the generator It is necessary to know the size of W when using dynamic behavior. It is also used as a parameter to be identified. 1.2 Parameter to be identified. Separability discussion System identification is generally characterized by input and output relationships. In the parameter identification process, identification parameters may not appear. The only one or the parameter is inseparable, and only the parameter to be identified is separable, and the identification result has practical significance. The following discusses the separability of the identification parameters from the physical concept. First, the input and output data measured by the test are the basis of the system identification. The key test data provided by the dynamometer load test are: high and medium pressure valve opening. Degree two h, M; regulation level pressure pe; generator active power measured by the power transmitter Pe. There is a dynamic link between the measured value of the generator active power P* and the true value Pe, ie: Tm is The inertia time constant of the power transmitter can be identified by an additional off-line test, which can be seen as a known parameter. For the inertia of the high-pressure cylinder volume, the input two h and the output Ph are the test measurements. Data, so it is possible to uniquely estimate the volume time constant T, h. input high and medium pressure valve opening two h, under the excitation of two Mt, the information has been reflected in the system output generator active power measurement value > e, such as Shown.

a. The delay and descent change process of the initial stage of electric power measurement Pe is related to the steam volume of the cylinder volume and the dynamometer inertia during the valve closing process. The dynamic characteristic parameters involved are Tsh, TsMl, Toh and ToMl. The parameters can be separated and estimated. Therefore, the amplitude change process of the phase-attenuated oscillation after the parameter ra can be separated from Pe reflects that the initial power angle W of Cd is closely related to the period of P* decay oscillation of the first stage after the dynamometer load-shedding. In summary, it is feasible to identify the main dynamic characteristic parameters of the steam turbine generator set by the dynamometer load test. 1.3 Identification of the main dynamic characteristic parameters based on genetic algorithm The steam turbine generator set is a nonlinear system, the traditional system identification technology. For example, least squares estimation, Kalman filtering and other effective methods are mostly applicable to linear systems. For nonlinear systems, only a linear approximation method can be adopted, which is easy to generate multiple solutions and convergence problems. An adaptive global optimization probability search algorithm with good global convergence, and its determined parameters have global optimality The characteristics and the better robustness of the identification process are as follows: a. Determine the parameters to be identified and their constraints: In the turbine generator set model, the parameter T to be identified is determined according to the prior knowledge. The constraint condition XmiS Xmax can be determined. The objective function: J(X)=, where Z=T, is the measured data of the dynamometer load test, W is the weight matrix, and N is the chromosome coding method that determines the feasible solution by counting the number of samples: using the binary coding method, the advantages of this method In order to include the largest number of patterns, the genetic algorithm can process the most patterns in the determined size group, and the encoding and decoding operations are simple and easy, and the genetic operations such as crossover and mutation are easy to determine from the objective function to the individual fitness. Conversion rules: The individual fitness F(X)=-J(X) is selected according to the size relationship, and the individual with the highest fitness among several individuals is selected to be inherited into the next generation group. In the selection operation, there is only a comparison operation between the individual fitness, no arithmetic operation, so it is easier to avoid the "early convergence" phenomenon to determine the crossover operator than the general selection operator: using the one-point crossover method, A commonly used crossover operator is to randomly set only one intersection point in an individual code string, and then exchange part of the chromosomes of two paired individuals at that point. It is characterized in that individuals with higher individual adaptability are more likely to maintain the influence of determining the mutation operator: using the simplemutation method, that is, randomly assigning a certain gene or genes with a certain mutation probability in the individual coding string. The gene values ​​on the seat are subjected to mutation operations to determine the relevant operational parameters of the genetic algorithm: population size M termination evolution algebra T cross probability pc and mutation probability.

2 Turbine generator set dynamic characteristic parameter identification example This paper based on the steam turbine generator set dynamometer load test simulation data has done a lot of identification examples, Table 1 gives the partial identification results Table 1 steam turbine generator set dynamic characteristics parameters Identification result identification result Example 1 Real value estimation value Example 2 Real value estimation value Example 3 Real value estimation value Example 4 The true value estimation value is obtained from prior knowledge: Xmin = t, Xmax = T, and the genetic algorithm operation parameter is additionally selected: M=A large number of identification examples show that it is feasible to identify the main dynamic characteristics of the steam turbine generator set based on the measurement data of the dynamometer load test and the genetic algorithm, and the algorithm has high precision and is not sensitive to noise. 3 Conclusion a pair of turbo generator The dynamic characteristic parameters are discussed, and a large number of examples are used to conclude that the parameter identification is separable.

The identification method is used to obtain the dynamic characteristics of the turbine generator, and the genetic algorithm is applied to the parameter identification. The effect is good.

Based on the dynamometer load test, the main dynamic characteristics of the steam turbine generator set are identified, and the valuable resources of the dynamometer load test are fully utilized. It has practical significance for analyzing the dynamic characteristics of the steam turbine generator set.

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