配网电压互感器损坏机理及其影响因素研究

发布时间：2018-05-14 02:15

本文选题：电压互感器 + 中性点不接地系统　；参考：《重庆大学》2014年硕士论文

【摘要】：电压互感器是连接电网一次系统与二次系统的电气设备，安装在电网的各个节点上，向二次系统提供一次系统的电压信息，供运行监视使用。在我国，中性点不接地电网发生单相接地故障时，不用立即切除故障，可继续带电运行2个小时。在此期间经常发生电压互感器及其熔断器的损坏事故，严重威胁电网的安全运行。已有的研究认为事故原因是电压互感器电感与系统对地电容产生L-C串联铁磁谐振稳态过电流所致，并以此提出了在电压互感器上加装消谐器等抑制措施。但近年来事故依然频发，并随着电网的发展呈上升趋势，甚至出现了电压互感器与消谐器一起烧毁的情况。因此，研究不接地电网发生单相接地故障时，电压互感器异常损坏机理和抑制措施仍是一个十分重要的研究课题。本文针对目前配电网的结构特征，采用理论分析、动模实验和数值仿真计算相结合的方法，对中性点不接地电网中电压互感器异常损坏的机理进行研究，找出影响电压互感器发热的主要因素，并对电压互感器损坏的抑制措施进行分析。具体研究内容如下： ①对比分析了电压互感器的串联模型和并联模型，指出串联模型推导有误，难于成立；L-C串联铁磁谐振稳态过电流不是引起电压互感器异常损坏的主要原因。由此提出了按并联模型通过暂态过程来寻求电压互感器损坏的机理，提出是由暂态过电流导致电压互感器热稳固性破坏而烧毁，并找出了对电压互感器发热有较大影响的几个因素：中性点不接地电网电压互感器的损坏主要是由系统发生单相间歇性接地故障导致系统状态的频繁切换所产生的暂态冲击电流引起的。由于电磁式电压互感器铁心的非线性，间歇性接地故障使铁心进入饱和区，接地故障发生瞬间产生的励磁涌流和故障消失后的电容电流作用在电压互感器绕组上，由此带来的巨大热量有可能造成电压互感器损坏。 ②分别对工程中常用的两种电压互感器进行了静态特性和暂态特性实验，，对电压互感器的损坏机理进行验证。实验结果表明：稳定的单相接地不会产生过大的稳态电流，不足以使电压互感器损坏；而在电压切换的暂态过程中，在电压互感器内产生的暂态冲击电流可以达到额定电流的百倍以上，在该电流的反复作用下，足以使熔断器熔断，甚至使电压互感器烧毁。 ③根据动模实验结果，分析了影响暂态冲击电流的因素，对电压互感器的发热进行了仿真计算。通过改变各影响因素的取值，计算在不同的情况下系统发生单相间歇性接地过程中电压互感器的发热量。利用正交试验的方法，对发热值进行了直观分析和方差分析，找到了对发热影响最严重的因素——系统线路长度。系统的线路越长，故障消失后的冲击电流越大，对电压互感器发热的影响越严重。 ④对抑制电压互感器损坏的措施进行了理论分析和动模实验验证：通过改善电网的运行方式，减小分区电容和在电网中性点加装适当容量的消弧线圈，可以有效地避免电压互感器异常损坏的现象。对应于中性点不接电网中的电压互感器，应完善其制造规范：按中性点不接地电网发生单相间歇性接地故障，对电压互感器进行热稳固性校验，这必将减少电压互感器损坏的几率。
[Abstract]:The voltage transformer is an electrical equipment connecting the primary system and the two system. It is installed on each node of the power grid and provides a system voltage information to the two system for operation monitoring. In our country, when a single phase grounding fault occurs in the neutral point ungrounded power grid, the fault can not be removed immediately and can continue to live for 2 hours. During this period, the damage accidents of voltage transformer and its fuse often occur, which seriously threaten the safe operation of the power grid. The existing research considers that the cause of the accident is that the inductance of the voltage transformer and the system to the ground capacitance produced by the L-C series ferromagnetic resonance steady current, and put forward the suppression measures such as installing the harmonic eliminator on the voltage transformer. But in recent years, the accidents are still frequent, and with the development of the power grid is rising, and even the situation of the voltage transformer and detuner burning together. Therefore, the study of the abnormal damage mechanism and the suppression measures of the voltage transformer is still a very important research topic when the single-phase grounding fault occurs in the ungrounded power grid.
In view of the structure characteristics of the current distribution network, the mechanism of the abnormal damage of voltage transformer in neutral grounding grid is studied by means of theoretical analysis, dynamic model experiment and numerical simulation. The main factors affecting the heating of the voltage transformer are found out, and the measures to restrain the damage of the voltage transformer are analyzed. The specific research contents are as follows:
The series model and parallel model of the voltage transformer are compared and analyzed. It is pointed out that the series model is inaccurate and is difficult to be established. The main reason for the abnormal damage of the voltage transformer is that the L-C series ferromagnetic resonance steady-state overcurrent is not the main cause of the abnormal damage of the voltage transformer. The transient overcurrent causes the thermal stability of the transformer to destroy and find out several factors which have great influence on the heating of the voltage transformer. The damage of the voltage transformer in the neutral point ungrounded power network is mainly the transient shock current caused by the frequent switching of the system state caused by the single phase intermittent grounding fault occurring in the system. Due to the nonlinearity of the iron core of the electromagnetic voltage transformer, the intermittent grounding fault causes the core to enter the saturation area. The excitation inrush current and the capacitive current after the fault disappear on the ground fault occur on the voltage transformer winding. The resulting great heat may cause the damage of the voltage transformer.
The static and transient characteristics of the two common voltage transformers used in the engineering are tested respectively, and the damage mechanism of the voltage transformer is verified. The experimental results show that the stable single-phase grounding will not produce excessive steady state current and can not cause the damage of the voltage transformer; while the voltage switching transient process, the voltage is in the voltage. The transient impact current produced in the transformer can reach more than 100 times the rated current, which is sufficient to fuse the fuse and even destroy the voltage transformer under the repeated action of the current.
Thirdly, according to the experimental results of the dynamic model, the factors affecting the transient impact current are analyzed, and the heating of the voltage transformer is simulated. The calorific value of the voltage transformer is calculated by changing the value of the influence factors. The calorific value of the transformer is calculated by the orthogonal test. Through visual analysis and analysis of variance, the most serious factor, the length of the system line, is found. The longer the line of the system is, the greater the impact current after the failure is, the more serious the effect on the heating of the voltage transformer.
(4) the theoretical analysis and dynamic model test of the measures to suppress the damage of the voltage transformer are verified: by improving the operation mode of the power grid, reducing the zoning capacitance and adding the appropriate capacity of the arc suppression coil at the neutral point of the power grid, the abnormal damage of the voltage transformer can be avoided effectively. It is necessary to improve its manufacturing specification: a single phase intermittent grounding fault occurs in the neutral point ungrounded power grid, and the thermal stability of the voltage transformer is checked, which will reduce the probability of the damage of the voltage transformer.

【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM451

【参考文献】