大型高科技工廠低壓配電系統地電流之特性分析

Analysis of the Ground Current Characteristics of Low Voltage Distribution System in the Large High-Tech Plants

張萬祥(Wan-Siang Chang)

指導教授 ： 周至如

中原大學/工學院/電機工程研究所/碩士(2004年)

https://doi.org/10.6840/cycu200400209

摘要

摘 要

大型科技廠的配電系統之電纜線及設備分佈各處，此系統在正常運轉時仍難免有些電流流入地中而形成所謂的地電流，地電流在廠內接地系統到處流竄可能干擾廠內的敏感系統與設備，甚至造成危險，為防範地電流的危害及干擾，必先瞭解地電流的特性，才能有效的防範。為此，本文探討地電流的特性包括地電流的分佈及其在接地系統(地網)上所造成的地電位昇及導體電流，以及在地面上所造成的磁場、步間電壓及接觸電壓等之分佈並初步評估對人員與敏感系統及設備的影響。大型科技廠內的配電系統通常包括特高壓、高壓及低壓配電系統，其中低壓配電系統與敏感設備最密切且地電流最嚴重，故為本文探討的對象。文中首先介紹地電流的成因及其影響，然後針對典型的三相五線式配電系統建立電路模型，以分析地電流的分佈。電路模型將考慮三相導體線、中性線、設備接地線及電纜線架等之接地點接地阻抗、導體之阻抗及相互之間的互阻抗，在分析過程中將再考慮不同的條件，包括中性線單點接地及多重接地、線架之接地阻抗變化、設備接地線的有無，以及負載不平衡度等。根據地電流的分佈，本文進一步應用接地電磁分析軟體“CDEGS”來模擬前述各項特性，並比對模擬值與容忍值來初步評估其影響。研究結果顯示，低壓配電系統正常運轉下的地電流雖不致傷害人員的安全，但對敏感的系統與設備確有干擾的虞慮，尤其在中性線多點接地且負載不平衡下，地電流更大，其所造成的地電位昇及磁場準位相當高，故必須防範其干擾，地網導體電流及各接地點的電流也值得注意，敏感系統與設備的接地點及裝設位置可參考這些數據來決定。
關鍵字：大型科技廠、低壓配電系統、地電流、地電位昇、磁場

關鍵字

大型科技廠 ； 地電流 ； 低壓配電系統 ； 磁場 ； 地電位昇

並列摘要

Abstract

In the large high-tech plants, the distribution system has many cables, wires and apparatus being allocated everywhere. Some currents from the system will flow into ground to form the so-called ground currents which flow through everywhere of grounding system in the plant to interfere the sensitive equipments and systems and even producing hazards. It is necessary to understand the characteristics of ground current for preventing the hazards and interference. For this, the thesis investigate the characteristics of ground currents which include the distributions of ground current, the ground potential rise and conductor current distributed on the grounding system (ground-grid) , and the magnetic fields, step voltage and touch voltage distributed on the ground surface. The affections of these characteristics on personnel and sensitive equipments and systems are also evaluated briefly. The distribution systems in the large high-tech plants usually include very high voltage (VHV), high voltage and low voltage distribution systems in which the low voltage distribution system is the subject of the study due to with large ground current and close relations with the sensitive equipments. The root causes of ground current and its affections are first described. Then, the circuit model to represent the typical three-phase five-wire (3 5W) distribution system is constructed for analyzing the ground current distribution. All the ground points, self and mutual impedances of three-phase cables, neutral wires, equipment grounding wires and the cable tray are considered in the circuit model. Various conditions including single-point and multi-point grounding of neutral lines, the different grounding impedances of cable tray, the use of equipment grounding wires and the load unbalances are taken into account in the analysis of ground current distribution. According to the ground current data from the circuit model, the other characteristics of ground current mentioned above are analyzed by a software called “CDEGS” which is based on the electromagnetic field analysis of grounding system. Finally, the affections of ground current characteristics are evaluated briefly by comparing between the data obtained from simulation and the tolerance values. The study results show that the ground currents due to low voltage distribution at normal operation will not damage the personnel but may interfere the sensitive equipments and systems. Especially, very high levels of ground currents, ground potential rises and magnetic fields due to neutral line with multi-point grounding and unbalanced loading should be prevented for protecting the sensitive equipments and systems from interferences. It is also necessary to refer the conductor currents of ground-grid and the ground current at each ground point for determining the grounding points and locations of sensitive equipments and systems.
Keywords：Large high-tech plants, low voltage distribution systems, ground current, ground potential rise, magnetic field

並列關鍵字

magnetic field ； ground current ； low voltage distribution systems ； ground potential rise ； Large high-tech plants

參考文獻

[62] 林南瑞, "大型科技廠接地系統之接地故障特性研究" , 中原電機

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