電氣專業(yè)畢業(yè)設(shè)計(jì)外文翻譯-wenkub
2023-06-16 05:41:38 本頁(yè)面
【正文】 reduce the frequency of serious incidents liable to result in the generating equipment being unavailable, even if these is no direct bearing on safety.l To reduce the frequency of incidents likely to have consequences to safety , in practice, the design principles for nuclear units based on Defence In Depth and the presence of barriers are such that serious accidents could only result from a simultaneous bination of independent and improbable incidents.In terms of nuclear safety, the principal objectives of operational feedback are as follows: to identify precursor incidents leading to more serious accidents in order to define and implement any corrective measures required before any such accidents occur. to take adventage of standardized units (the generic aspects of incidents, deriving maximum benefit from modification studies, ect ) to ensure, in cases where modification is necessary, that these are no adverse secondary effects before principle is extended to the entire plant series. to utilize data gathered during actual operation of the installation in order to unify the level of safety, especially in the case of a new plant series.The guidelines on which EDF has based its operational experience feedback system are as follows:i. To systematically gather the maximum amount of data and circulate it as widely as possible, particularly within EDF.ii. To bring together as many as possible Designers. Operators, Manufacturers and Safety Authorities in the data analysis process.iii. To lean from experience on order to benefit not only those units planned or under construction but also units currently in service.。 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
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