The power system dynamic test involves a large number of multi-units, and the requirements can not affect the normal operation of the system, especially the further improvement of the power market. The importance of power system safety is increasingly significant, so it cannot be artificially tested on the actual system. The digital simulation of power system is widely used in the research of dynamic problems of power systems because of its economical, convenient and expandable advantages. Especially for the problem of multi-machine large system dynamics, which is difficult to solve by theoretical analysis, digital simulation has become Recognized analytical methods However, if there is no verification of the field measured data, the correctness of the simulation results is questionable. CW.Taylor found that using the current WSCC database is not enough to simulate the oscillation and disintegration of the system in the 1996 Western Power Grid blackout accident. The DC transmission control of the simulation system is modified. The governor and voltage control of the AGC large unit After the load model, the simulation results are consistent with the actual situation of the system.

With the development and popularization of microcomputer technology, there are more and more on-site observation devices, and these devices can monitor the abnormal state of the system. Every abnormality in the system can be regarded as a "natural" test of the system. The recorded disturbance and output data are very valuable. We can use these shared test data for analysis and research to test our own theory. And model, to establish an understanding of the unknown mechanism Therefore, a large number of measurement and recording equipment must be installed in a system to perform complete and reliable disturbance data recording, while fully taking into account and using the measured data on site.

The low-frequency oscillation problem of the power system involves the dynamics of the whole system. It is closely related to the rotating machinery and control system of the generator, but it is difficult to obtain their accurate parameters. It is difficult to obtain convincing conclusions from simple theoretical analysis. Therefore, the test method is adopted. Analysis is especially important.

A number of large-scale power oscillations have occurred, seriously threatening the safety of power plants and systems. After the PSS is installed, there are two oscillations. The oscillation has some special points. For example, the oscillation occurs without obvious disturbance in the system, and the oscillation can disappear automatically without human intervention. The oscillation starts and disappears quickly. In the oscillation to maintain the equal amplitude and other aspects of the analysis, it is considered that the oscillation is not a negative damping form of the oscillation, nor is it caused by load fluctuations, but what is the oscillation mechanism, it is still inconclusive. This paper proposes a suitable low frequency oscillation. The experimental method of the study is combined with the example of the security line oscillation. The results show that the proposed test method is an effective method for analyzing the low-frequency oscillation problem. 1 The experimental analysis method of low-frequency oscillation first extracts the characteristics of the test data, and then analyzes it by using the existing theory. And according to the experimental system conditions, the simulation results are compared with the measured data. When the comparison is consistent, it indicates that the oscillation conforms to the existing theory; when the results do not match, it is not perfect according to the characteristics of the measured data. Theory, and get the oscillation through simulation, and then with the measured data

Therefore, the Prony algorithm can be used to process the measured data, and the accurate actual oscillation mode and characteristics can be obtained. 1.2 Theoretical analysis After obtaining the oscillation characteristics of the measured data, a series of theoretical analysis is needed to determine the possible causes of the oscillation. The possible causes of low frequency oscillation can be divided into the following types: the existing negative damping theory. Including the long distance of the transmission line, the system using heavy excitation system, the system has periodic load switching, and the PSS parameter design is unreasonable.

The perfect nonlinear theoretical analysis of non-negative damping theory includes: Hopf bifurcation theory, that is, the stability limit of low-frequency oscillation of power system is related to the Hopf bifurcation of system differential equation; chaos theory, because power system is a standard The nonlinear system with the possibility of chaos is further studied in the case of forced resonance caused by torque harmonics. The shaft system speed control system and excitation system have the possibility of generating resonance.

In view of the above various theories, simulation calculation is needed, and the simulation results are tested. 1.3 Results Verification If the simulation results are similar to the measured data, it indicates that the reason of the simulation oscillation may be the actual oscillation cause. How to judge the similarity of the oscillation curve is a problem worth studying. It is not completely scientific to calculate the mean square error of the two curves. For example, when representing the key points of the curve, it should have a heavier weight coefficient. Since the Prony algorithm can extract the characteristics of the oscillating signal, the Prony algorithm can be used to extract the characteristics of the signal when judging the simulation effect, and then the features are compared, which is more scientific.

When a similar Prony analysis is found, it explains the possible causes and the observations of the actual system. This is the only criterion for determining whether the analysis is correct. Sometimes the re-emergence of the oscillation can promote the further analysis of the theoretical analysis. This is an example of the oscillation of the Henan Nanwang security line from the practice to the theory and the rational analysis of the example. The test method of the above oscillation analysis is used to carry out the actual measurement data. On March 16, 2000, a low-frequency oscillation occurred in the security line of the Shangan Power Plant in the southern power grid of Hebei Province to Baoding North Station. With the help of the Hebei Electric Power Dispatching Communication Center, the active waveform of the fault recording data of the Shang’an unit was obtained. The time interval between the two points is 0. 02s. In the Prony analysis, the analysis results of the bifurcation data according to the stable oscillation and attenuation sections are as shown in Table 1. The amplitude of the time range/Hz attenuation factor is the initial phase. According to Table 1, it can be concluded that the oscillation mode of the security line oscillation is: a is weakly damped during the oscillation process, the attenuation factor is -0.0146, and the stable oscillation is characterized by a large amplitude oscillation of about 18 Hz. The amount of AC exceeds the amount of DC (the AC component in Table 1 appears as a conjugate pair). The oscillation decay process is very fast, and the attenuation factor reaches about -0.

2.2 Theoretical analysis 2.1 One of the modes involved in the small disturbance analysis machine and the No. 4 machine is 1.16 Hz, which is very close to the measured main frequency of the measured oscillation obtained by Prony analysis. Therefore, it can be considered that this oscillation conforms to the oscillation mode. The participating units are: No.1 and No.2 of Matou Power Plant, No.4, No.5, No.8 and No.9 of Xingtai Power Plant, 220kV system of No.1 and No.2 of Hengshui Power Plant and 110kV of No.1 of Wangkuai Power Plant. Distributed in various areas of the south network of Hebei, so the oscillation mode can be considered as the oscillation between the upper unit and the system, which can be simplified into a single machine infinite form during the analysis process, or at least the two-machine form 22.2 damping analysis through the excitation system Analysis, the obtained 1.16Hz oscillation mode, when the excitation regulator amplification factor changes within a large range, the real part of the oscillation mode is negative and large (-0. 26~-0.48), indicating that the system damping is large enough It does not cause oscillation in the form of negative damping. Considering that the PSS is installed in the field, it does not generate negative damping. The measured data of the analysis is as follows: the frequency component is a small amplitude oscillation (-d 0146) process, which shows how the system damping of the weak damping phenomenon “disappears” is an unusual problem. At the same time, without human intervention, Very large attenuation (-0.84) at the end stage is also difficult to understand. 22.3 Simulation analysis Firstly, various disturbances are applied to the simulation system, trying to reproduce the negative damping oscillation of the existing principle, including the coincidence of the loader end and the opposite side three-phase short circuit. The machine end load switching, adjusting the excitation adjustment system parameters, reducing the generator d-axis transient short-circuit time constant Td", etc. may stimulate the amplitude oscillation in the normal operating state, but will not cause the actual oscillation of the security line and follow The imperfect resonance oscillation principle is simulated, and the disturbance is applied to the power output of the prime mover, indicating that under certain disturbances, the prime mover power and the electromagnetic power on the rotor are not equal, and the torque is unbalanced, causing the rotor to accelerate or decelerate. Then the disturbance disappears, but the disturbance induces a continuous attenuation of the rotor vibration. Generally, the vibration frequency of the rotor is lower than that of the low frequency vibration. High, but when the frequencies of the two kinds of oscillations are close, it may cause beat vibration, such as the bending vibration of the shafting and the vibration of the torsional vibration. The frequency of the beat may be close to the natural oscillation frequency. Mechanical vibration, 0.05, application time is 8s~17s, oscillation frequency is 1.63Hz natural oscillation frequency of the system. 2.3 Simulation results verify that the above waveform has certain similarity with the measured waveform. In order to verify, the simulation results are Prony analysis. The oscillating part, so the simulation data is also analyzed from the stable oscillation.

The analysis results are shown in Table 2, in which the first segment is the stable oscillation part, and the second segment is the attenuation part. The measured data is compared with the simulation data as shown in Table 3. The time period amplitude frequency / Hz attenuation factor initial phase segment Time period measured simulation frequency / Hz attenuation factor frequency / Hz attenuation factor stable oscillation end oscillation As can be seen from Table 3, in the steady oscillation process, the frequency and attenuation of the two curves are very close, and the attenuation is also fast, so it can be concluded that: The vibration of the security line is in line with the resonance type low-frequency oscillation. Through the above analysis, an imperfect mechanism explanation of the oscillation of the security line is found through the test method, and the actual data is obtained. Only the small value of the output of the gas turbine can be superimposed. Zhen Wei. The amplitude is blishingj. This paper puts forward the analysis of the low-frequency oscillation using the å«” method. The combination of the analysis of the unexplained oscillation of the security line proves that the application of the test method to analyze the measured low-frequency oscillation is a useful supplement and verification for the theoretical analysis. The research to solve the cause of low-frequency oscillation in the field provides a powerful tool to obtain a theory according to the test method. It must be tested in practice, and the actual measurement is carried out on site. A synchronous recording device such as a rotor speed control system is added to observe whether there is such a This will be a further work in the future.

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