在電力變壓器差動保護中,主要關(guān)注的是如何成功地識別勵磁涌流。本文提出了一種基于離散小波變換的內(nèi)部故障與涌流的判別方法。應(yīng)用小波變換將差動電流分解為多階頻帶的細節(jié)系數(shù);通過對不同的涌流和內(nèi)部故障情況的研究分析,發(fā)現(xiàn)在細節(jié)系數(shù)變化顯著的情況下,故障條件是最有可能的。這一事實被用來建立一個判斷標準,將相對小波能量定義為特征量以提取不同不同時刻的特征。另外,以能量變化量為基礎(chǔ),在兩個連續(xù)的時間間隔內(nèi)對相對小波能量的值進行了比較監(jiān)測,在這一差異不是很顯著量的情況下則認為是勵磁涌流。在MATLAB仿真平臺上進行了該算法的性能評估,并對不同的瞬態(tài)情況進行了仿真實驗。

【文章頁數(shù)】：67 頁

【學位級別】：碩士

【文章目錄】：
摘要
ABSTRACT
CHAPTER 1 INTRODUCTION
    1.1 Background
    1.2 Research Status and Problem Statement
        1.2.1 Harmonic Restraint
        1.2.2 Flux, Voltage Restraints and Transformer Inductance Scheme
        1.2.3 Wave Shape Recognition Methods
        1.2.4 Pattern Recognition Methods
            1.2.4.1 Artificial Neural Network
            1.2.4.2 Fuzzy System
    1.3 Research Significance and Objective
    1.4 Thesis layout
CHAPTER 2 DIFFERENTIAL PROTECTION AND INRUSH CURRENT
    2.1 Introduction
    2.2 Differential Protection
        2.2.1 The Principle of Differential Protection
        2.2.2 CTs and CTs Connections
        2.2.3 Differential Protection Considerations
    2.3 The Percentage Differential Protection
        2.3.1 Implementation of Percentage Differential Protection
        2.3.2 Percentage Differential Protection Challenges
    2.4 Transformer Inrush Current
        2.4.1 The Nature of the Inrush Current
        2.4.2 The Inrush Current Characteristics
        2.4.3 Analysis of the Inrush Current
CHAPTER 3 THE APPROACH OF INRUSH CURRENT IDENTIFICATION
    3.1 Introduction
    3.2 Wavelet Transform
        3.2.1 Introduction
        3.2.2 Discrete Wavelet Transform DWT
        3.2.3 DWT and Filters Bank
    3.3 Power System Configuration
        3.3.1 Power Transformer Model
        3.3.2 Proposed Electric Power System
    3.4 Proposed Approach
        3.4.1 Relative Wavelet Energy
        3.4.2 Discrimination Criterion
CHAPTER 4 EVALUATION THE PERFORMANCE OF THE APPROACH
    4.1 Introduction
    4.2 Results and Discussion
        4.2.1 The Case of Energizing the Power Transformer (Inrush Current)
        4.2.2 The Case of Internal faults at the Power Transformer Terminals subsequent to its Energization
        4.2.3 The Case of Internal faults at the Power Transformer Terminals during Normal Operation
CHAPTER 5 CONCLUSION AND FUTURE WORK
    5.1 Conclusion
    5.2 Future Work
REFERENCES
ACKNOWLEDGEMENT



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