城市电缆化率对配电网的中性点接地方式及故障特性影响的研究

发布时间：2018-10-08 06:42

【摘要】：配电网中性点的接地方式问题和很多方面都有着密切的关系,如供电可靠性,安全性,绝缘等问题。这些年来,配电网的电缆化率很大程度的升高,这使得网络中的电容电流也随之增加,间歇性弧光接地产生的故障比例增大,为了解决这些问题,提出对中性点接地方式进行改进。随着新兴接地方式的推出,新的问题也随之产生。如何在现有情况下改进单相接地故障模型,并提出更完善的接地方式是值得研究的问题。同时在研究实际工况时发现,当变压器的中性点采用经过间隙来接地时,负载存在的电动机在发生接地故障时,产生反馈作用,导致零序电压增大且无法衰减到安全值,间隙保护动作,变压器被切除,线路重合闸后,由于变压器断开,线路的正常运行就会受到影响。本文针对变压器的中性点如何接地的选择又进行了一定的研究。首先,在了解了现今存在的电弧模型的基础上,对电缆化率较高的情况下发生频率较高的间隙性电弧接地故障进行数学模型的推导分析,进一步改进,并使用仿真软件进行仿真分析验证,得到更完善的单相接地故障模型;其次,研究了现存的各种中性点接地方式的基础上,在在电缆化率升高的情况下,分析每一种中性点接地方式存在的缺陷和不足,提出改进的接地方式。并使用仿真分析软件进行处理分析,将第一步中所改进的故障模型应用到此处的线路中代替传统单相接地故障。最终得到一种改进的接地方式,称为消弧线圈分时段并联电阻接地方式。在新的中性点接地方式下,研究原有接地方式的保护配置,找出不合理的地方,对继电保护配置进行完善;接着,本文又针对变压器的中性点处的接地结构进行了分析,以实际配电网中出现的问题为出发点,研究变压器的间隙保护,并研究电动机负荷的反馈作用对变压器中性点接地布局的影响,使用仿真软件进行分析,从负载的变化角度来研究变压器中性点处电气量,最终得出变压器采用经间隙接地的初步量化安全条件。
[Abstract]:The grounding mode of neutral point in distribution network is closely related to many aspects, such as power supply reliability, safety, insulation and so on. Over the years, the cable conversion rate of the distribution network has increased greatly, which makes the capacitance current in the network also increase, and the proportion of faults caused by intermittent arc grounding increases. In order to solve these problems, The improvement of neutral grounding mode is proposed. With the introduction of new grounding methods, new problems also arise. How to improve the single-phase grounding fault model and put forward a more perfect grounding mode is worth studying. At the same time, it is found that when the neutral point of transformer is grounded by gap, the motor with load has feedback effect when grounding fault occurs, which leads to the increase of zero-sequence voltage and the failure to attenuate to the safe value. Gap protection operation, the transformer is removed, the line reclosing, because the transformer is disconnected, the normal operation of the line will be affected. In this paper, how to select the neutral point of transformer is studied. First of all, on the basis of understanding the existing arc model, the mathematical model of the high frequency gap arc grounding fault with high cable conversion rate is deduced and analyzed, which is further improved. A more perfect single-phase grounding fault model is obtained by using the simulation software. Secondly, on the basis of the existing neutral grounding methods, under the condition of the increase of cable conversion rate, a more perfect single-phase grounding fault model is obtained. The defects and shortcomings of each neutral grounding method are analyzed, and an improved grounding method is proposed. The improved fault model in the first step is applied to replace the traditional single-phase grounding fault. Finally, an improved grounding method, called arc-suppression coil with parallel resistance in different periods, is obtained. Under the new neutral grounding mode, the protection configuration of the original grounding mode is studied, the unreasonable place is found out, and the relay protection configuration is improved. Then, the paper analyzes the earthing structure of the neutral point of the transformer. Based on the problems in the actual distribution network, the gap protection of transformer is studied, and the influence of motor load feedback on the neutral grounding layout of transformer is studied, and the simulation software is used to analyze it. From the point of view of load variation, the electrical quantity at the neutral point of transformer is studied, and the preliminary quantitative safety condition of transformer grounding through gap is obtained.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM862

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