本文選題：電壓互感器 + 中性點不接地系統(tǒng)　； 參考：《重慶大學》2014年碩士論文

【摘要】：電壓互感器是連接電網(wǎng)一次系統(tǒng)與二次系統(tǒng)的電氣設備，安裝在電網(wǎng)的各個節(jié)點上，向二次系統(tǒng)提供一次系統(tǒng)的電壓信息，供運行監(jiān)視使用。在我國，中性點不接地電網(wǎng)發(fā)生單相接地故障時，不用立即切除故障，可繼續(xù)帶電運行2個小時。在此期間經常發(fā)生電壓互感器及其熔斷器的損壞事故，嚴重威脅電網(wǎng)的安全運行。已有的研究認為事故原因是電壓互感器電感與系統(tǒng)對地電容產生L-C串聯(lián)鐵磁諧振穩(wěn)態(tài)過電流所致，并以此提出了在電壓互感器上加裝消諧器等抑制措施。但近年來事故依然頻發(fā)，并隨著電網(wǎng)的發(fā)展呈上升趨勢，甚至出現(xiàn)了電壓互感器與消諧器一起燒毀的情況。因此，研究不接地電網(wǎng)發(fā)生單相接地故障時，電壓互感器異常損壞機理和抑制措施仍是一個十分重要的研究課題。 本文針對目前配電網(wǎng)的結構特征，采用理論分析、動模實驗和數(shù)值仿真計算相結合的方法，對中性點不接地電網(wǎng)中電壓互感器異常損壞的機理進行研究，找出影響電壓互感器發(fā)熱的主要因素，并對電壓互感器損壞的抑制措施進行分析。具體研究內容如下： ①對比分析了電壓互感器的串聯(lián)模型和并聯(lián)模型，指出串聯(lián)模型推導有誤，難于成立；L-C串聯(lián)鐵磁諧振穩(wěn)態(tài)過電流不是引起電壓互感器異常損壞的主要原因。由此提出了按并聯(lián)模型通過暫態(tài)過程來尋求電壓互感器損壞的機理，提出是由暫態(tài)過電流導致電壓互感器熱穩(wěn)固性破壞而燒毀，并找出了對電壓互感器發(fā)熱有較大影響的幾個因素：中性點不接地電網(wǎng)電壓互感器的損壞主要是由系統(tǒng)發(fā)生單相間歇性接地故障導致系統(tǒng)狀態(tài)的頻繁切換所產生的暫態(tài)沖擊電流引起的。由于電磁式電壓互感器鐵心的非線性，間歇性接地故障使鐵心進入飽和區(qū)，接地故障發(fā)生瞬間產生的勵磁涌流和故障消失后的電容電流作用在電壓互感器繞組上，由此帶來的巨大熱量有可能造成電壓互感器損壞。 ②分別對工程中常用的兩種電壓互感器進行了靜態(tài)特性和暫態(tài)特性實驗，，對電壓互感器的損壞機理進行驗證。實驗結果表明：穩(wěn)定的單相接地不會產生過大的穩(wěn)態(tài)電流，不足以使電壓互感器損壞；而在電壓切換的暫態(tài)過程中，在電壓互感器內產生的暫態(tài)沖擊電流可以達到額定電流的百倍以上，在該電流的反復作用下，足以使熔斷器熔斷，甚至使電壓互感器燒毀。 ③根據(jù)動模實驗結果，分析了影響暫態(tài)沖擊電流的因素，對電壓互感器的發(fā)熱進行了仿真計算。通過改變各影響因素的取值，計算在不同的情況下系統(tǒng)發(fā)生單相間歇性接地過程中電壓互感器的發(fā)熱量。利用正交試驗的方法，對發(fā)熱值進行了直觀分析和方差分析，找到了對發(fā)熱影響最嚴重的因素——系統(tǒng)線路長度。系統(tǒng)的線路越長，故障消失后的沖擊電流越大，對電壓互感器發(fā)熱的影響越嚴重。 ④對抑制電壓互感器損壞的措施進行了理論分析和動模實驗驗證：通過改善電網(wǎng)的運行方式，減小分區(qū)電容和在電網(wǎng)中性點加裝適當容量的消弧線圈，可以有效地避免電壓互感器異常損壞的現(xiàn)象。對應于中性點不接電網(wǎng)中的電壓互感器，應完善其制造規(guī)范：按中性點不接地電網(wǎng)發(fā)生單相間歇性接地故障，對電壓互感器進行熱穩(wěn)固性校驗，這必將減少電壓互感器損壞的幾率。
[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.

【學位授予單位】：重慶大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TM451

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