【作者】 陈军；

【导师】 李永丽；

【作者基本信息】 天津大学 ， 电力系统及其自动化， 2005， 硕士

【摘要】 随着越来越多的超高压远距离输电线路在我国的建成和运行,大容量变压器的应用也日益增多。电力变压器在电力系统输电和配电各个环节中广泛使用,因而也就对变压器保护的可靠性和速断性提出了更高的要求。差动保护是变压器保护的主保护,变压器在空载合闸或外部故障切除后恢复供电时,差动回路会流入励磁涌流,若差动保护不能识别并躲过此电流,就会发生误动。因此,励磁涌流的识别一直也是国内外继电保护工作者的研究热点。本文先变压器励磁涌流的成因进行了较为详细的论述。随后分类介绍了以电气量和现代信号处理方法为手段的多种涌流识别方法,并对每种方法做了分析和评价。接着,本文通过对励磁涌流和故障电流波形的分析和比较,提出了一种通过比较波形不对称系数来识别励磁涌流和故障电流的新原理。根据该原理分别建立了单相变压器涌流、三相变压器对称涌流和三相变压器单向涌流的简化数学模型,并从理论上推导出基于波形不对称系数的变压器涌流判别定值。由于故障电流具有正弦波的特征,因而其波形不对称系数近似为零。当故障电流中含有衰减直流分量,并考虑波形初相角因素的影响时,不对称系数会变大但不会超过0.1。而涌流的波形不对称系数一般在0.15左右,仅在个别情况下,由于间断角过小,波形不对称系数会低于0.15,但采用“或”门制动的方法可以有效的对保护进行闭锁。文章最后借助MATLAB的电力工具箱进行了双端供电系统的空载合闸和区内、区外故障仿真,并用本文提出的原理进行涌流和故障电流的鉴别。大量仿真试验表明,该变压器涌流鉴别法,原理清晰,计算简单,容易在微机保护中实现,而且算法本身具有滤除衰减直流分量,抑制高次谐波,抗CT饱和以及不受系统频率偏移影响等优点。更多还原

【Abstract】 As EHV power network is developing rapidly, large capacity power transformers are used widely in the transmission system and distribution system. Therefore, high performance and high reliability of power transformer protection are required urgently. At present, the main protection of internal faults of the power transformer is the differential protection. When the unloaded power transformer is switched on the power system or in the process that a fault, outside the protected zone, is cleared, the magnetizing inrush current will usually produced. The differential protection relays will maloperate. So it is still a research focus for relaying researchers in the world. This paper analyses the origin of inrush current appearance, and introduces many methods based on electric parameters and modern signal processing technology. Then a new method of identifying inrush current based on waveform asymmetric coefficient is described in detail. According to this method, we build simplified mathematic models of one-sided inrush current and symmetrical inrush current separately and figure out the theoretical definite value to identify the inrush current. Because the internal fault current is symmetrical, so its waveform asymmetric value is less than 0.10, even if the waveform contains decay DC component and influenced by initial phase angle of source voltage. Meanwhile the dead angle of inrush current makes the inrush current asymmetric, so its asymmetric coefficient is big and greater than 0.15 in most conditions. “Or-gate” brake can be used to block the protection maloperation in which the asymmetry coefficient is small when the dead angle is obscure. In the end, many simulations prove the correctness of this method in an actual two-source power system by using MATLAB. The simulations indicate that this method is legible and easy to be used in microcomputer protection, otherwise it has the advantages of filtering decay DC component, suppressing disturbance of high harmonics, resisting CT saturation, and being unacted on the deviation of system frequency.更多还原