【作者】 樊淑娴；

【导师】 徐丙垠；

【作者基本信息】 山东大学 ， 电力系统及其自动化， 2011， 博士

【摘要】 有源配电网能充分利用分布式发电技术的优点,发挥其对配电网的积极作用,节省电力系统的整体投资,满足用户对电能日益增长的需要,是未来配电网发展的方向。在有源配电网中,分布式电源并网运行会带来一系列问题,孤岛(Islanding)就是其中之一。孤岛运行时,供电电压和频率得不到保障,线路继续带电会影响故障电弧的熄灭、重合闸动作,危害事故处理人员的人身安全等,所以有源配电网中必须配备孤岛保护,以在系统出现孤岛运行后将分布式电源从电网中切除。在有源配电网中,消弧线圈自动跟踪补偿,即跟踪实际电网电容电流的大小,实时调整消弧线圈的电感,使系统在发生单相接地故障后,消弧线圈产生的感性电流能够完全补偿系统对地电容产生的容性电流,使接地点电流减小,利于接地点电弧的自行熄灭,降低故障的危害程度,是保证电网可靠运行的一种重要技术措施。单相接地故障选线,即在系统发生单相接地故障后,尽快找出故障线路,在进行必要的负荷转移后,人为地将接地设备从系统中切除,能防止故障引起的过电压危害系统绝缘,引发更为严重的短路故障,是减少故障损失,提高配电网供电可靠性和用户满意度的一种主要技术措施。目前,己提出多种孤岛保护方法,其中的载波孤岛保护方法,易于实现,对分布式电源输出电能质量影响较小,且适用于分布式电源高度渗透的有源配电网,有很好的应用前景,但保护可靠性较差,存在误动和拒动的可能,离实用化还有一定距离,因此,研究出一种检测盲区小、实用性能高的基于注入信号的孤岛保护方法,对有源配电网的发展有着重要的意义。传统配电网中的系统对地电容检测方法均可适用于有源配电网,其中的信号注入法应用较为广泛,但实用效果却不太理想,存在测量精度较差和操作较复杂的缺点,有待进一步研究。传统配电网中的单相接地故障选线方法,除了基于负序分量的方法外,均适用于有源配电网,其中信号注入法的应用最为广泛,但从实用的情况来看,选线准确率还比较低,因此,研究出一种新的方法,提高选线准确率是有待进一步研究的课题。另一方面,采用信号注入法实现孤岛保护、系统对地电容检测和单相接地选线,都需要从系统母线侧向系统注入信号,这使得将孤岛保护、消弧线圈跟踪补偿和单相接地故障选线装置一体化综合设计成为可能,这样不仅可以减少硬件设备、节约成本,还可以避免注入信号相互干扰、优化各自的工作性能,而注入信号类型与频率的选择、注入与检测方式、综合利用算法则是需要深入研究的问题。本文探讨利用信号注入法实现孤岛保护、系统对地电容检测与单相接地选线,提高孤岛保护、接地选线可靠性与系统对地电容检测的精确度；研究信号注入方法的综合利用,以简化系统构成,减少成本。具体的研究工作主要有：(1)提出将孤岛保护、消弧线圈自动跟踪补偿和单相接地故障选线装置一体化综合设计,不仅可以减少硬件设备、简化装置接线,而且便于不同技术、功能之间的相互配合,从而获得优化的工作性能。(2)提出了载波闭锁式孤岛保护方案。在过/欠压保护和过/欠频保护的基础上增加载波闭锁措施,提高保护灵敏度和可靠性,减小检测盲区,并针对母线孤岛时保护拒动的情况,提出检测母线孤岛并停发载波信号的措施。该保护方案灵敏度高、检测速度快、简单方便、易于实现、对电网电能质量负面影响小,而且适用于不同并网形式的分布式发电系统。(3)提出了一种注入恒流信号的系统对地电容检测、计算方法。利用消弧线圈内置电压互感器向系统注入一恒流恒频信号,通过检测中性点信号电压,直接计算出系统对地电容,为实现消弧线圈自动跟踪补偿奠定了基础。该方法不需要对消弧线圈本身进行操作、不需要对信号源进行任何调节,操作方便、计算准确、响应速度快、不会对系统的正常运行产生不利影响。利用上述方法计算系统对地电容的同时,还可以计算出系统的对地绝缘电阻,求出系统自身的阻尼率,进而用于系统在线绝缘监视。(4)提出了一种注入方波信号的谐振接地系统单相接地故障选线方法。通过从故障相TV向系统注入一特定频率的恒流方波信号,探测各支路零序电流,并分析其基波与三次谐波电流幅值之间的关系来选择故障线路。该方法具有较强的排除系统对地电容影响的能力,大大提高了检测精度,在系统发生高阻接地故障时,仍有较高的选线准确率,而且只需检测各线路自身的零序电流即可判断是否为故障线路,具有“自具”特点。(5)提出了方波信号的频率选取方法,这是利用注入方波信号法实现故障选线的关键和前提。考虑配电网的要求,设计了信号发生装置,产生恒流基波和三次谐波信号,且做到和配电网互不影响,使所提出选线方法的实际应用成为可能；提出了能够方便消除工频及各次谐波干扰而灵敏、精确地检测出注入信号的信号处理方法,为进行准确的故障选线打下了基础。(6)综合考虑所提出的载波闭锁式孤岛保护、注入恒流信号的系统对地电容检测方法和注入方波信号的单相接地故障选线方法,提出了信号注入法综合应用方案,通过选择可共用的注入信号方式、类型和频率,同时满足三种功能的需要,达到信号注入法综合应用的目的。这样,可避免注入信号相互干扰,影响各自的工作性能,且能降低成本,减少对配电网计量、检测等的影响。(7)论证了利用消弧线圈内置电压互感器注入信号,实现孤岛保护和单相接地故障选线的可行性,以及注入方波信号的可共用性,确定了共用信号方式、类型和频率；设计了一体化装置,孤岛保护所用的注入信号源,选线功能所采用的注入信号源、检测主机等和计算对地电容所用的信号源、检测主机均为同一装置,在该装置内几种功能配合完成,并在分布式电源并网处安装有孤岛保护检测及控制主机,且对装置各组成部分的功能进行了介绍；最后,对装置各部分的工作流程进行了说明。本文提出的载波闭锁式孤岛保护、注入恒流信号的系统对地电容检测方法和注入方波信号的谐振接地系统单相接地故障选线方法,能够很好地解决现有技术存在的问题,而对信号注入法的综合应用,则可进一步节约成本,优化不同技术的性能。本文的研究成果对于推进有源配电网保护与监控技术的发展、提高供电可靠性具有十分重要的意义。更多还原

【Abstract】 In active distribution network, the advantages of distribution generation (DG) can be applied very well and DGs can play a positive effect on distribution network, reduce the overall investment of power system and satisfy the increasing requirement of electric power, so the active distribution network is the development trend of the future distribution network. But in active distribution network, some problems will arise due to the interconnection of DGs, islanding operation is one of them. While islanding operation occurs, the supplied voltage and frequency can’t be guaranteed, the fault arc extinction and reclosing will be influenced due to that the feeder in islanding continues to be alive, and the equipments of power system and maintenance workers may be damaged. Therefore, islanding protection should be applied in active distribution network, which can disconnect DGs from distribution network while islanding operation occurs. In active distribution network, automatic tuning of arc suppression coil (ASC), namely, the current caused by ASC can completely compensate the current caused by distributed capacitance while a single-phase grounding fault occurs by tracking the capacitive current and adjusting ASC in real-time, is an important technique measure to ensure distribution network operating reliably. Fault line selection, namely, fault line should be identified quickly and the fault should be removed manually after the necessary loads are transferred while a single-phase grounding fault occurs, can avoid the system insulation being damaged by the over voltage caused by the fault and more serious phase-to-phase fault occurring, so it is an important technique measure to reduce the loss caused by the fault and improve power supply reliability.At present, a lot of islanding protection methods have already been proposed, in which, carrier islanding protection has good application prospect due to that it is easy to implement, has little effect on output power quality of DGs and can apply to active distribution network that many DGs are interconnected into. But the protection has poor reliability and may cause mal-operation and fail to trip, so it still has some way from application. Therefore, a new islanding protection method based on signal injection which has smaller non-detection zone and higher practicability is important for the development of active distribution network. All of the methods of distributed capacitance detection in traditional distribution network are suitable for active distribution network. Among which, the methods based on signal injection are widely used, but they have either poor measurement accuracy or complicated manipulation, and their applications are ineffective, so they need to be gone into further research. All of the methods of fault line selection in traditional distribution network can apply to active distribution network except those which based on negative-sequence components. Among which, the methods based on signal injection also have wide application, but the practical effects show that the accuracies are low. Therefore, a new method which has higher accuracy needs to be developed. Moreover, it can be known that signals need to be injected from the substation bus while islanding protection, distributed capacitance detection and fault line selection based on signal injection are adopted, so it makes the integrative design of the three devices become possible. Thus, it can not only decrease hardware equipments and reduce cost, but also avoid the injected signals interfering with each other and optimize each performance, so the selection of the shared signal type and frequency, signal injection mode, signal detection method and comprehensive application also should be studied.In this paper, methods based on signal injection oriented islanding protection, distributed capacitance detection and fault line selection are studied to improve the reliability of islanding protection and fault line selection, also the measurement accuracy of distributed capacitance. And the comprehensive application of signal injection methods is studied to simplify the structure of system and reduce the cost. The details of the research work are as follows:(1) Bring forward a new integrated design idea synthesizing three kinds of technology including islanding protection, automatic tuning of ASC, and fault line selection in active distribution network, which not only can simply the hardware architecture and wiring of equipments, but also improve the cooperation of different technical and functions to obtain optimum performance.(2) Propose carrier based islanding protection method, which adds carrier blocking in(on) the basis of over/under voltage protection and over/under frequency protection to improve sensitivity and reliability and reduce the non-detection zone, and stops injecting carrier signal in bus islanding to avoid the protection failing to trip. This method has characteristics of high sensitivity, simple principle, easy realizing, and small influence on the power quality, and also it is suitable for DGs in different grid-connected way. (3) Put forward a new method of distributed capacitance detection to lay the foundation for automatic tuning of ASC by injecting a constant current signal from the secondary side of voltage transformer of ASC and detecting the voltage of neutral point to calculate the distributed capacitance. The method needn’t adjust ASC manually or regulate the signal source. It has features of being easy to operate, high calculation accuracy, fast response and no negative impact on the system. While calculating distributed capacitance using the above method, we can also estimate the insulation resistance of the system to obtain damping rate for the on-line monitor of the system insulation.(4) Propose a new method of fault line selection based on square wave in resonance grounding system. The method can identify the fault line by injecting a constant current square wave into system through the fault phase of TV, detecting zero sequence current of each branch and analyzing the relationship between fundamental current and the 3rd harmonic current. The method is almost free from the influence of distributed capacitance, and has high sensitivity and accuracy for the faults with high impedance grounded. And this method can judge the fault line only using the zero current of the fault line itself.(5) Proposed the frequency selection criteria of the injected square wave is the premise and key of the fault line selection method; considering the requirements of distribution system, signal injection equipment is designed to make the proposed fault line selection method put into practical application, which can not only put out constant current fundamental signal and the 3rd harmonic signal, but also have little influence on the system; signal processing method is developed to lay the foundation for selecting fault line accurately, which could detect the injected signal with sensitive precision and eliminate various harmonic interference effectively.(6) Considering the three proposed methods including carrier based islanding protection, distributed capacitance detection based on constant current signal, and fault line selection based on square wave, a comprehensive application scheme of signal injection methods is developed, which is implemented by selecting the shared signal injection mode, signal type and signal frequency satisfy the needs of the three functions. Thus, it can avoid the injected signals interfering with each other and the working performances are influenced, also it can reduce the cost and decrease the influence on the measurement and detection of power system.(7) To satisfy the design requirements that islanding protection, distributed capacitance detection and fault line selection are integrated in one device, the feasibilities of realizing islanding protection and fault line selection with signal injecting from the voltage transformer of ASC and with the same square wave were proved. The signal source employed to islanding protection, the signal source and detection system employed to automatic tuning of ASC, and the signal source and detection system employed to fault line selection are all integrated in one device which can implement all functions, besides, a detection and control system are installed in the grid-connected point of DG. Finally, the functions and the flow charts of each components of the device are introduced.The three methods proposed in this paper, including carrier based islanding protection, distributed capacitance detection based on constant current signal, and fault line selection based on square wave, can solve the problems existed in each technique. The development of the comprehensive application of signal injection methods can reduce the cost and obtain better performance. The researches of this paper are of great importance in pushing on the developments of the protection and monitor technology of active distribution network and improving the supplied reliability of power system.更多还原