【作者】 马勇；

【导师】 陈俊武；

【作者基本信息】 华中科技大学 ， 高电压与绝缘技术， 2011， 硕士

【摘要】 中压配电网中性点接地方式是个综合性的技术问题,它关系到系统过电压、绝缘配合、通信干扰、故障选线、系统可靠性和安全性等很多方面。近年来,随着经济的快速发展,电网规模的不断扩大,电力电缆的大量使用,使得配电网系统对地等效电容电流增加,传统接地方式在新形势的发展下呈现出诸多问题。例如采用消弧线圈补偿配电网对地等效电容电流后带来选线困难和无法有效抑制过电压,配电网系统规模的变化,原有消弧线圈不再满足补偿要求等问题。针对以上问题,灵活接地方式(消弧线圈并联小电阻)和分布式补偿方式这两种新型接地方式被提出。灵活接地方式在单相接地故障时补偿系统电容电流,并联小电阻后可抑制过电压同时提供有效的故障选线依据,集合了中性点经消弧线圈接地和小电阻接地两种接地方式的优点;分布式补偿方式通过在线路末端分布安装消弧线圈,解决了系统消弧线圈增容改造中空间不够等多方面问题,同时可减小故障残流,降低安装成本。本文在简要分析灵活接地方式理论的基础上,利用PSCAD/EMTDC建立20kV配电网典型模型,包括电弧接地故障模型和故障多次重复计算模型等,考虑故障类型、小电阻并入时间和故障发生时刻等因素影响,对灵活接地方式下发生单相接地故障后系统过电压做了仿真计算。结果表明:可根据故障相电压波形对故障类型进行判断,在中性点电压为0左右并入小电阻时系统过电压最小。本文介绍了分布式补偿方式的特点之后,利用PSCAD/EMTDC建立20kV配电网典型模型,从安装位置和补偿容量方面,与主站消弧线圈配合等方面研究了单相接地故障电流分布式补偿的特性,以及进行分布式补偿对系统发生断线过电压的影响。结果表明:分布式补偿装置安装在最大电容电流线路末端,且补偿容量与该线路的电容电流相对应时,故障点的残流最小;分布式补偿线路的断线过电压可通过主站消弧线圈过补偿和增加阻尼电阻的方法来抑制。结合理论研究,本文从结构、原理等方面介绍了适合分布式补偿方式的接地变压器兼消弧线圈一体化装置,并将该装置进行了变电站现场调试。结果表明:适合于分布安装的接地变压器兼消弧线圈一体化装置结构简单,成本较小,易于分布安装,与系统对地等效电容、主站消弧线圈共同构成了零序电流回路,现场实际应用证明其能满足系统单相接地的补偿要求。灵活接地方式和分布式补偿方式针对配电网发展带来的新问题,能将故障电流补偿至允许的范围,将系统过电压抑制在有效范围,提高系统安全性和可靠性,为配电网服务。更多还原

【Abstract】 Neutral grounding of medium voltage level distribution networks is a comprehensive technical problem, which is important to the system’s overvoltage, insulation coordination, communication jamming, fault line selection, reliability and safety .Recently, with the rapid development of the economy, increasing of the expansion of power system, the vast amount of using of electric cable, the traditional grounding encountered a lot of new challenges because of the capacitance current distribution in phase short circuit to ground increasing sharply. For example, there are difficulties in fault line selection and overvoltage suppression, and the old Petersen Coil no longer meet the current. In view of the questions mentioned above, flexible grounding and distributed compensation come up.Capacitive current is compensated by the flexible grounding, and overvoltage is reducing by a parallel low resistance. At the same time, it can be helpful for fault line selection, which includes the advantages of neutral earthing via Petersen Coil and neutral grounded with Low-resistance. Installing the Petersen Coil at the end of line, distributed compensation could fix up the problems in expanding the capacity of Petersen Coil, lower cost.After introducing the brief theories of flexible grounding, based on the PSCAD software, a simulation model on the neutral flexible grounded in distribution network is presented, which includes intermittent arc earthing model, multiple runs model, and so on. The overvoltage of system is calculated by the model, thinking about single phase-to-ground type, the time of paralleling resistor, and the moment of fault occurring. The results indicate that, fault type can be determined by the curve of faulty feeder, the overvoltage of system would be smallest if the small resistor is paralleled when neutral voltage is zero.After introducing the brief characteristics of distributed compensation, flexibility of distributed arc suppression coil is studied by the location and capacity, and cooperation with arc extinction coil of principal station, and a simulation model is calculated. The result shows that fault current is smallest when distributed compensated at the end of line with suitable capacity. Broken line overvoltage can be restrained by over compensation and adding damping resistor.Combined with the theoretical research, this paper introduces the Structure and Principle of the grounding transformer and the arc suppression coil integrated devices, and does an experiment. This device has features such as simple structure, low cost, convenient installment. Through test and actual application shows that i t can fulfill the requirement.Flexible grounding and distributed compensation could compensate the fault current, improve the security and reliability of the system, servicing for the distribution network.更多还原