電氣專業(yè)畢業(yè)設(shè)計外文翻譯-文庫吧
2025-05-16 05:41 本頁面
【正文】 了明確的陳述。按照安全重要系統(tǒng)（IPS）進行一項詳盡無疑的分析，同樣也是為了確定哪一種設(shè)備需要進行定期的檢測，哪一項無需檢測（正常運行就是運行狀況良好的充分證明）。對每個系統(tǒng)和每次檢測來說，《檢測程序》文件對操作程序， 操作標(biāo)準(zhǔn)和要求檢測的周期等都作了明確的規(guī)定，這些規(guī)定成了運行人員制定檢測計劃表的基礎(chǔ)。提高安全水平，操作經(jīng)驗反饋由EDF采用的標(biāo)準(zhǔn)政策（EDF是一種主要PWR系統(tǒng)類型和有限的單個電廠序列數(shù)量）可保證通過特別重視預(yù)兆的分析極大的提高操作經(jīng)驗的價值。這有雙重目的： 1． 減少能夠引起發(fā)電設(shè)備不能用的事故發(fā)生頻率，即使這些事故可能對安全沒有直接關(guān)系； 2． 減少可能對安全造成后果的嚴重事故的發(fā)生頻率，實際上，以“多層保護”和故障存在為基礎(chǔ)的核機組設(shè)計原理，認為嚴重的事故只能是那些單獨事故和那些所謂不可能發(fā)生的事故同時發(fā)生的產(chǎn)物。從核安全的角度考慮，操作反饋的主要目標(biāo)如下：1 確認可導(dǎo)致更為嚴重事故的預(yù)兆事故，以明確和貫徹在這類事故發(fā)生前所需采取的改正措施；2 利用標(biāo)準(zhǔn)的機組（事故的一般方面，從修改研究等方面獲取最大的效益）3 如有必須修改之處，那么在將原理推廣到整個電廠序列之前，要保證不會產(chǎn)生相反的副作用；4 要利用在機組實際運行中所獲得的數(shù)據(jù)，以統(tǒng)一安全標(biāo)準(zhǔn)，特別是對新廠更需要如此。EDF是按如下方針制定其操作經(jīng)驗反饋系統(tǒng)的：1 系統(tǒng)地收集盡可能多的數(shù)據(jù)資料，盡可能廣泛地交流收集到的數(shù)據(jù)，特別是在EDF范圍內(nèi)；2 在數(shù)據(jù)分析過程中，要盡可能地讓設(shè)計人員，運行人員，制造廠商和安全機構(gòu)一起參與；3 吸取經(jīng)驗，這不僅有益于那些正在計劃和建設(shè)中的機組，而且有益于那些目前正在運行的機組。 Groundfault circuit breakerThe grounding methods we have covered so far are usually adequate,but further safety measures are needed in some foe example , that a person sticks his finger into a lamp socket ().Although the metal enclosure is securely grounded, the person will still receive a painful shock. Or suppose a 120 V eletric toster tumbles into a swimming pool. The heating elements and contacts will produce a hazardos leakage current throughout the pool ,ven if the frame of the toaster is securely grounded. Devices have been developed that will cut the source of power as soon as such accidents occur. These groundfault circuit breaker will typically trip in 25 ms if the leakage current exceeds 5 mA. How do these protective devices operate ? A small current transformer surrounds the live and neutral wires as shown in . The secondary is connected to a sensitive electronic detetor that can trigged a circuit breaker CB that is in series with the 120 V line. Under normal conditions the current Iin the line conductor is exactly equal to thecurrent Iin the neutral ,and so the net current (II) flowing through the hole in the toroidal core is zero. Consequently, no flux is produced in the core, the induced voltage E is zero, and breaker CB does not trip. Suppose now that a fault current I leaks directly from the live wire to ground . This could happen if someone touched a live terminal (). A fault current I would also be produced if the insulation broke down between a motor and its grounded enclosure . Under any of these conditions, the net current flowing through the hole of the CT is no longer zero but equal to I or I. A flux is set up and a voltage E is induced, which trips CB. Because an imbalance of only 5 mA has to be detected, the core of the transformer must be very permeable at low flux densities. Supermalloy is often used for this purpose because it has a relative permeability of typically 70000 at a flux density of only 4mT . rapid conductor heating: the It factor It sometimes happens that a current far greater than normal flows for a brief period in a conductor . The Ilosses are than very larg
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