Research On The Signal Detection System Of Optical Votage Transformer

Compared with the traditional voltage transformer, optical voltage transformer possesses apparent advantages in transient characteristics and anti-interference. The problem of optical voltage transformer in its signal detection system is, however, one of the obstacles that restrict its application in smart grid. Especially in the small-signal detection, interferential noise and temperature drift will both reduce the accuracy of signal detection. In the future development, optical voltage transformer may be combined with devices of primary side, and therefore optic sensing head needs to go through a small-processing, which is exactly one of the applications that research on improving small-signal detection accuracy. On the other hand, the grid may have instant voltage drops and other processes during the transient process. The purpose of accurately reflecting the voltage waveform also belongs to small-signal detection treatment.The main research points in this thesis include the following.To begin with, focusing on the special system of optical voltage transformer, this thesis analyzes the main source of interferential noise in the signal detection system and the signal and noise characteristics in the signal processing system. Based on these, it will research on the signal modulation methods for the system: AC and DC modulations. What is more, the advantages and disadvantages of both modulations in the system will be analyzed. The simulation research on the application of both AC and DC modulation technologies in the signal detection system will be carried out. The simulation model based on the detection of dual optical path system will be built and corresponding simulation researches will be carried out. Considering the characteristics that the systematic noise and signal have the spectrum overlapping and that when there is any fault, the sudden voltage drop will lead to the strong noise and weak signals , the fact that in the small signal detection system the output SNR of AC modulation is better than that of DC modulation will be proved.Furthermore, this thesis researches on the influence of imbalance of the dual optical path on the signal detection system. It analyzes, in the detection system of dual optic path, the error characteristics due to different kinds of losses and to component matching disorders and other intrinsic factors and then puts forward the method to calculate balancing factors by means of the rms of 50Hz signal. In the process of dynamic balancing, the corresponding error curve is going to be drawn according to the co-influence from both the fluctuations of the frequency of voltage and relative displacement of the dual path signals and to the balancing errors resulted from non-integral period sampling. Furthermore, this thesis will comparatively analyze the advantages of using the window function to reduce errors of balancing factors and the simulation research on the error curve after the window function is introduced. Next it will analyze which window function has the best compensating effect on balancing factors.Last but not least, this thesis carries out an overall design of the signal detection1 system of optical voltage transformer and its simulation research will be implemented too. Focusing mainly on characteristics of signal transmission in different stages, simulations of different parts and digital filter in the signal detection system will all be designed and the model for the designed detection processing system will be built and its corresponding simulations will be applied. The simulation verification of the voltage when it suddenly drops to 1% of its rated value.