【正文】 本來帶有絕緣材料但是因?yàn)閾p壞的電氣設(shè)備的殼體或者是某種支架的時(shí)候，就會(huì)發(fā)生觸電的危險(xiǎn)。通常來說，按照規(guī)定用于接地的電阻應(yīng)該小于4歐，而人體本身的電阻就比較大，不小于1000歐姆，因此短路電流流過裝設(shè)的接地裝置的時(shí)候電流非常的大，而我們?nèi)梭w所流過的電流就非常的小了。所以這樣就會(huì)降低電器設(shè)備漏電以后人體觸電的危險(xiǎn)。 中性點(diǎn)接地方式110kV及以上電壓等級的電力系統(tǒng)，均屬于大電流接地系統(tǒng)，中性點(diǎn)直接接地系統(tǒng)。中性點(diǎn)直接接地的系統(tǒng)中，當(dāng)發(fā)生一點(diǎn)接地故障時(shí)，即構(gòu)成單相接地短路，這時(shí)所產(chǎn)生的故障電流很大，所以稱大電流接地系統(tǒng)。10kV以下電壓等級的電力系統(tǒng)，均屬于小接地電流系統(tǒng)，中性點(diǎn)不與接地裝置連接或經(jīng)過消弧線圈、電壓互感器以及高電阻與接地裝置連接的高壓電力系。統(tǒng)稱小接地短路電流系統(tǒng)。 中性點(diǎn)接地原則中性點(diǎn)直接接地是將發(fā)電機(jī)或變壓器的中性點(diǎn)直接與接地裝置連接，或中性點(diǎn)經(jīng)小阻抗與接地裝置連接。系統(tǒng)中全部或部分變壓器中性點(diǎn)直接接地，是大接地電流系統(tǒng)的標(biāo)志，其主要目的是降低對整個(gè)系統(tǒng)絕緣水平的要求。當(dāng)中性點(diǎn)接地變壓器臺(tái)數(shù)，容量及其分布情況變化時(shí)，系統(tǒng)零序序網(wǎng)也隨之變化，因此同一點(diǎn)故障時(shí)，零序電流的分布也隨之變化。所以變壓器中性點(diǎn)接地情況的變化，直接影響到零序電流保護(hù)的靈敏度。因此，變壓器中性點(diǎn)接地原則：1．不使零序網(wǎng)有較大的變化，以保證零序電流保護(hù)有穩(wěn)定的靈敏度。 2．不使系統(tǒng)出現(xiàn)危險(xiǎn)的過電壓； 結(jié) 論經(jīng)過十幾周的認(rèn)真學(xué)習(xí)與工作，終于完成了本次畢業(yè)設(shè)計(jì)——某水泥廠110kV變電所設(shè)計(jì)。這十幾周的學(xué)習(xí)生活是充實(shí)且快樂的。通過本次畢業(yè)設(shè)計(jì)，不但將以前所學(xué)的知識(shí)回顧了一遍，而且在設(shè)計(jì)過程中參閱了大量的相關(guān)資料，學(xué)習(xí)了不少新的知識(shí)。本次設(shè)計(jì)主要內(nèi)容包括：負(fù)荷計(jì)算與無功補(bǔ)償、短路電流計(jì)算、電氣主接線的設(shè)計(jì)、電氣設(shè)備的選擇與校驗(yàn)（包括主變壓器的選擇、斷路器及隔離開關(guān)的選擇與校驗(yàn)、導(dǎo)體的選擇與校驗(yàn)、電流互感器的選擇與校驗(yàn)和電壓互感器的選擇等）和變配電所的布置與結(jié)構(gòu)設(shè)計(jì)。其中，主接線代表了變電配所的主體結(jié)構(gòu)，它對各種電氣設(shè)備的選擇、配電裝置的布置、繼電保護(hù)、自動(dòng)裝置和控制方式的擬定都有決定性的關(guān)系，并將長期影響電力系統(tǒng)運(yùn)行的可靠性、安全性、靈活性和經(jīng)濟(jì)性。本次的系統(tǒng)設(shè)計(jì)所涉及的內(nèi)容繁多，目前所掌握的只是其中很少的一部分。通過本次畢業(yè)設(shè)計(jì)，使我對所學(xué)專業(yè)有了更深入的了解。同時(shí)，也使我明白到自己的不足。在以后的學(xué)習(xí)和工作中，我會(huì)更加努力的學(xué)習(xí)專業(yè)知識(shí)，提高自己的專業(yè)技能，切實(shí)做到理論與實(shí)際相結(jié)合。謝辭本畢業(yè)設(shè)計(jì)是在任老師的悉心指導(dǎo)下完成的，論文的全過程傾注了老師大量的心血和汗水，再此對任老師所給予我們仔細(xì)認(rèn)真、愛崗敬業(yè)的精神表示誠摯的感謝！畢業(yè)設(shè)計(jì)是檢驗(yàn)和鍛煉學(xué)生實(shí)際工程設(shè)計(jì)能力的一項(xiàng)教學(xué)環(huán)節(jié)。在此次設(shè)計(jì)中，綜合運(yùn)用所學(xué)知識(shí)，認(rèn)真學(xué)習(xí)了相關(guān)書籍，注重理論聯(lián)系實(shí)際。在任老師的耐心指導(dǎo)下，按時(shí)完成了此次設(shè)計(jì)，培養(yǎng)了綜合運(yùn)用基礎(chǔ)知識(shí)和技能解決實(shí)際問題的能力，初步掌握了工程設(shè)計(jì)的方法，為將來的工作奠定了基礎(chǔ)。在此期間，各位老師，特別是任老師為我做了大量的輔導(dǎo)和答疑工作，幫我解決了設(shè)計(jì)過程中的一個(gè)個(gè)難題，使設(shè)計(jì)工作順利完成。同時(shí)，在本次設(shè)計(jì)及論文的寫作過程中，同學(xué)們也為我提供了力所能及的幫助，并創(chuàng)造了濃厚的學(xué)習(xí)氛圍！再次感謝任老師悉心的指導(dǎo)和同學(xué)們的熱心幫助。此次設(shè)計(jì)及論述過程中難免有錯(cuò)誤和不妥之處，敬請各位老師批評指正。附 錄某水泥廠總降壓變電所的主接線圖參考文獻(xiàn)[1] ：機(jī)械工業(yè)出版社，2001[2] ：冶金工業(yè)出版社，2003[3] ：吉林科學(xué)技術(shù)出版社，1985[4] ：中國電力出版社，2004[5] ：水利電力出版社，1978.[6] ：內(nèi)蒙古人民出版社，1992[7] ：水利電力出版社，1991[8] ：水利電離出版社，1985[9] ，2010[10] ：中國水利水電出版社，2003[11] ：中國電力出版社，2004[12] ：中國電力出版社，2006[13] ：機(jī)械工業(yè)出版社，1983[14] ：機(jī)械工業(yè)出版社，2000[15] ：中國電力出版社，2004[16] ：中國電力出版社 2008[17] ，機(jī)械工業(yè)出版社，2002[18] ：機(jī)械工業(yè)出版社，1993[19] ：機(jī)械工業(yè)出版社，1990[20] ：上?？茖W(xué)技術(shù)出版社，1992[21] ：機(jī)械工業(yè)出版社，2008[22] ：中國電力出版社，2002外文資料翻譯Reliability of Lightning Resistant Overhead Distribution Lines Lighting continues to be the major cause of outages on overhead power distribution lines. Through laboratory testing and field observations and measurements, the properties of a lightning stroke and its effects on electrical distribution system ponents are wellunderstood phenomena. This paper presents a pilation of 32 years of historical records for outage causes, duration, and locations for eight distribution feeders at the Oak Ridge National Laboratory (ORNL) .Distribution type lightning arresters are placed at deadend and angle structures at pole mounted wormer locations and at high points on the overhead line. Station class lightning arresters are used to protect underground cable runs, pad mounted switchgear and unit substation transformers. Resistance to earth of each pole ground is typically 15 ohms or less. At higher elevations in the system, resistance to earth is substantially greater than 15 ohms, especially during the dry summer months. At these high points, ground rods were riven and bonded to the pole grounding systems in the 196039。s in an attempt to decrease lightning outages. These attempts were only partially successful in lowering the outage rate. From a surge protection standpoint the variety of pole structures used (inline, corner, angle, dead end, etc.) and the variety of insulators and hardware used does not allow each kV overhead line to be categorized with a uniform impulse flashover rating (170 kV, etc.) or a numerical BIL voltage class (95 kV BIL。 etc.). For simplicity purposes in the analysis, each overhead line was categorized with a nominal voltage construction class (15 kV, 34 kV, or 69 KV). Six of the eight overhead lines (feeders 1 through 6) were built with typical REA Standard horizontal wood cross arm construction utilizing single ANSI Class 555 porcelain pin insulators (nominal 15 kV insulation). The shield angle of the overhead ground wire to the phase conductors is typically 45 degrees. One overhead line (feeder 7) was built with transmission type wood pole construction because the line extended to a research facility which was to have generated electrical power to feed back into the grid. Pole structure of this line are of durable wood cross a construction which utilize double ANSI 523 porcelain suspension insulators to support the conductors (nominal 34 kV insulation). The shield angle of the overhead ground wire to the phase conductors for feeder 7 is typically 30 degrees. In 1969, an overhead line (feeder 8) was intentionally built with lightning resistant construction in an attempt to reduce lightning caused outages. Pole structures of the line have phase over phase 24inch long fiberglass suspension brackets with double ANSI 523 porcelain suspension insulators to support the conductors (nominal 69 kV insulation). The shield angle of the overhead ground wire to the phase conductors for feeder 8 is typically 30 degrees. The failure data was piled for each of the eight kV feeders and is presented in Table, along with pertinent information regarding feeder construction, elevation, length, and age.A key finding of the failure analysis is that weatherrelated events account for over half (56%) of the feeder outages recorded. Fiftyseven of the 76 weatherrelated outages were attributed to lightning. Insulation breakdown damage due to lightning is also suspected in at least a dozen of the equipment failures observed. The data indicates overhead lines which pass over high terrain are less reliable because of the greater exposure to lightning. For example, feeder 3 had the most recorded outages (48), of which twothirds were due to weatherrelated events。 this feeder is also the highest line on the plant site, rising to an elevation of 450 above the reference valley elevation.