【摘要】：高壓直流輸電等能源互聯(lián)技術(shù),是清潔能源大規(guī)模接入和遠(yuǎn)距離運(yùn)送的重要技術(shù)保障。高壓直流輸電技術(shù)具有遠(yuǎn)距離、大容量等許多優(yōu)點(diǎn),隨著高壓直流輸電技術(shù)的迅猛發(fā)展,越來越多的問題也隨之而來。目前來看,交流電網(wǎng)中存在的直流分量問題就顯得日益突出。電磁式電流互感器是電力系統(tǒng)中十分重要的電力設(shè)備,它直接關(guān)系著電力系統(tǒng)的繼電保護(hù)的可靠運(yùn)行和電能計(jì)量的精確性。而直流偏磁效應(yīng)會給電流互感器帶來嚴(yán)重影響,因此研究和分析直流偏磁對電流互感器的影響就具有十分重要的意義。論文首先通過直流偏磁等效模型和電流互感器T型等效模型的建立,詳細(xì)分析了直流偏磁對電流互感器的影響。對于保護(hù)用電流互感器,它的作用是將系統(tǒng)的非正常狀態(tài)或故障狀態(tài)信息傳送到繼電保護(hù)裝置,所以必須重點(diǎn)關(guān)注它的暫態(tài)飽和特性。通過理論分析故障后電流互感器勵(lì)磁電流和磁通的關(guān)系,分析了直流偏磁和剩磁對電流互感器起始飽和時(shí)間的影響。其次,通過仿真實(shí)驗(yàn)進(jìn)一步驗(yàn)證了直流偏磁對保護(hù)用電流互感器的影響。通過電流互感器基本磁化曲線的模擬,利用MATLAB中Simulink仿真組件,搭建出電流互感器的仿真模型研究其暫態(tài)飽和特性。研究表明正向的直流偏磁會加速電流互感器的飽和,而反向的直流偏磁延緩電流互感器的飽和,并且隨著直流分量的加入,勵(lì)磁電流波形發(fā)生畸變,偶次諧波尤其是二次諧波增加明顯。再次,差動保護(hù)是變壓器的主保護(hù),而最常見的差動保護(hù)制動原理就是根據(jù)二次諧波制動。通過仿真分析出直流偏磁下,電流互感器飽和二次諧波含量增大,很容易導(dǎo)致繼電保護(hù)裝置拒動,影響電力系統(tǒng)安全。最后,對于計(jì)量用電流互感器,它的作用是將系統(tǒng)正常運(yùn)行時(shí)的電流傳送到測量設(shè)備,所以應(yīng)該重點(diǎn)關(guān)注其穩(wěn)態(tài)傳變特性。通過理論分析推導(dǎo)出電流互感器誤差受鐵心磁導(dǎo)率的影響,再根據(jù)鐵心磁導(dǎo)率和鐵心電感之間的關(guān)系設(shè)計(jì)實(shí)驗(yàn),測量直流偏磁下鐵心磁導(dǎo)率的變化。通過交流、直流混合的實(shí)驗(yàn)方法,分析直流偏磁對計(jì)量用電流互感器造成的誤差影響。實(shí)驗(yàn)結(jié)果證明,隨著直流分量的增大,鐵心磁導(dǎo)率減小,電流互感器誤差增大,角差和比值差都明顯增大。
[Abstract]:Energy interconnection technology such as HVDC transmission is an important technical guarantee for large-scale access and long-distance transportation of clean energy. HVDC technology has many advantages, such as long distance, large capacity and so on. With the rapid development of HVDC technology, more and more problems follow. At present, the problem of DC component in AC power grid is becoming more and more prominent. Electromagnetic current transformer is a very important power equipment in power system. It is directly related to the reliable operation of relay protection in power system and the accuracy of electric energy measurement. The DC bias effect will bring serious influence to the current transformer, so it is of great significance to study and analyze the effect of DC bias on the current transformer. Firstly, the influence of DC bias on current transformer is analyzed in detail through the establishment of DC bias equivalent model and T-type equivalent model of current transformer. For the protection current transformer, its function is to transmit the abnormal state or fault state information of the system to the relay protection device, so we must pay more attention to its transient saturation characteristics. The relationship between excitation current and flux of current transformer after fault is analyzed theoretically, and the influence of DC bias and remanence on the initial saturation time of current transformer is analyzed. Secondly, the influence of DC bias magnetic field on protection current transformer is verified by simulation experiment. By simulating the basic magnetization curve of the current transformer and using the Simulink simulation module in MATLAB, the simulation model of the current transformer is built to study the transient saturation characteristics of the current transformer. It is shown that the forward DC bias can accelerate the saturation of the current transformer, while the reverse DC bias will delay the saturation of the current transformer, and the excitation current waveform will be distorted with the addition of the DC component. The even-order harmonics, especially the second-order harmonics, increase obviously. Thirdly, differential protection is the main protection of transformer, and the most common braking principle of differential protection is based on second harmonic braking. Through simulation, it is found that the saturation second harmonic content of current transformer increases under DC bias, which can easily lead to the failure of relay protection device and affect the safety of power system. Finally, for the metering current transformer, its function is to transmit the current of the system under normal operation to the measuring equipment, so we should pay more attention to its steady-state transfer characteristics. Through theoretical analysis, it is deduced that the error of current transformer is affected by the permeability of core, and then the experiment is designed according to the relationship between core permeability and core inductance, and the change of permeability of core under DC bias is measured. The error effect of DC bias on measuring current transformer is analyzed by means of alternating current and direct current mixing experiment. The experimental results show that with the increase of DC component, the permeability of core decreases, the error of current transformer increases, the angle difference and ratio difference increase obviously.
【學(xué)位授予單位】：蘭州理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TM452

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