论文英文翻译
论文 英文文翻译
Guidance Notes for completing application formPart 1 Personal InformationEligibility to work at the British CouncilWe are only able to accept applications from individuals who have the right to work in the country to which they have applied.Personal InformationThe British Council’s normal retirement age is 65. If you are over this age, or within 6 months of it, at the time you apply to join us, in line with the Equality (Age) Regulations 2006, we will consider your application but reserve the right to reject it if we consider that we would be unlikely to derive sufficient benefit from your appointment in the period before your retirement.Criminal Convictions (UK)Subject to certain exempted occupations, convictions that are ‘spent’ under the Rehabilitation of Offenders Act 1974 need not be mentioned. Please be aware that declaring a conviction will not automatically disqualify you from being employed unless this post is subject to a Criminal Records Bureau Check.If the post is subject to a Criminal Records Bureau Check, British Council is committed to safeguarding and promoting the welfare of children and young people and expects all of its partners to share this commitment. Appointment to these roles are subject to enhanced Criminal Records Bureau (CRB) checks in the UK, and, where appropriate, equivalent systems overseas.Data ProtectionThe British Council will use the information you provide in this form to process your application. If your application is successful and you take up employment with the British Council, this form will be kept on your personnel file and some details from it will be held electronically by Human Resources in line with the Data Protection Act (1998). If your application is unsuccessful, this form willbe kept on file for one year after completion of the recruitment exercise and then securely destroyed.The British Council will treat all personal details in accordance with UK law and its own privacy policy. Under Data Protection law you have the right to ask for a copy of the information we hold on you, for which we may charge a fee, and the right to ask us to correct any inaccuracies in that information. If you do want more information about this please contact your local British Council office or the Data Protection Team dataprotection@. Part 2 Job-Related InformationDisabilityThe UK Disability Discrimination Act 1995 defines a person with a disability as someone who has a physical or mental impairment (including a learning or sensory impairment) that has a substantial and long term adverse effect on his/her ability to carry out normal day to day activities. In any country, it is British Council policy to interview all applicants who are disabled and who meet the essential criteria for an advertised job.Employment and professional informationPlease give details of your employment for the last 10 years, or since leaving full-time education if this is sooner, starting with the most recent employment. Account for all your time, including voluntary work or other periods away from work. Please be aware that it will not prejudice your application if you disclose a period of ill health or a period out of formal employment (e.g. time spent at home bringing up children).Other relevant experiencePlease note that this does not need to be limited to work experience. It can include experience of volunteering or of roles held within the community e.g. youth worker, community worker or leader etc..。
毕业论文英文参考文献与译文
Inventory managementInventory ControlOn the so-called "inventory control", many people will interpret it as a "storage management", which is actually a big distortion.The traditional narrow view, mainly for warehouse inventory control of materials for inventory, data processing, storage, distribution, etc., through the implementation of anti-corrosion, temperature and humidity control means, to make the custody of the physical inventory to maintain optimum purposes. This is just a form of inventory control, or can be defined as the physical inventory control. How, then, from a broad perspective to understand inventory control? Inventory control should be related to the company's financial and operational objectives, in particular operating cash flow by optimizing the entire demand and supply chain management processes (DSCM), a reasonable set of ERP control strategy, and supported by appropriate information processing tools, tools to achieved in ensuring the timely delivery of the premise, as far as possible to reduce inventory levels, reducing inventory and obsolescence, the risk of devaluation. In this sense, the physical inventory control to achieve financial goals is just a means to control the entire inventory or just a necessary part; from the perspective of organizational functions, physical inventory control, warehouse management is mainly the responsibility of The broad inventory control is the demand and supply chain management, and the whole company's responsibility.Why until now many people's understanding of inventory control, limited physical inventory control? The following two reasons can not be ignored:First, our enterprises do not attach importance to inventory control. Especially those who benefit relatively good business, as long as there is money on the few people to consider the problem of inventory turnover. Inventory control is simply interpreted as warehouse management, unless the time to spend money, it may have been to see the inventory problem, and see the results are often very simple procurement to buy more, or did not do warehouse departments .Second, ERP misleading. Invoicing software is simple audacity to call it ERP, companies on their so-called ERP can reduce the number of inventory, inventory control, seems to rely on their small software can get. Even as SAP, BAAN ERP world, the field ofthese big boys, but also their simple modules inside the warehouse management functionality is defined as "inventory management" or "inventory control." This makes the already not quite understand what our inventory control, but not sure what is inventory control.In fact, from the perspective of broadly understood, inventory control, shouldinclude the following:First, the fundamental purpose of inventory control. We know that the so-called world-class manufacturing, two key assessment indicators (KPI) is, customer satisfaction and inventory turns, inventory turns and this is actually the fundamental objective of inventory control.Second, inventory control means. Increase inventory turns, relying solely on the so-called physical inventory control is not enough, it should be the demand and supply chain management process flow of this large output, and this big warehouse management processes in addition to including this link, the more important The section also includes: forecasting and order processing, production planning and control, materials planning and purchasing control, inventory planning and forecasting in itself, as well as finished products, raw materials, distribution and delivery of the strategy, and even customs management processes.And with the demand and supply chain management processes throughout the process, it is the information flow and capital flow management. In other words, inventory itself is across the entire demand and supply management processes in all aspects of inventory control in order to achieve the fundamental purpose, it must control all aspects of inventory, rather than just manage the physical inventory at hand.Third, inventory control, organizational structure and assessment.Since inventory control is the demand and supply chain management processes, output, inventory control to achieve the fundamental purpose of this process must be compatible with a rational organizational structure. Until now, we can see that many companies have only one purchasing department, purchasing department following pipe warehouse. This is far short of inventory control requirements. From the demand and supply chain management process analysis, we know that purchasing and warehouse management is the executive arm of the typical, and inventory control should focus on prevention, the executive branch is very difficult to "prevent inventory" for the simple reason that they assessment indicatorsin large part to ensure supply (production, customer). How the actual situation, a reasonable demand and supply chain management processes, and thus set the corresponding rational organizational structure and is a question many of our enterprisesto exploreThe role of inventory controlInventory management is an important part of business management. In the production and operation activities, inventory management must ensure that both the production plant for raw materials, spare parts demand, but also directly affect the purchasing, sales of share, sales activities. To make an inventory of corporate liquidity, accelerate cash flow, the security of supply under the premise of minimizing Yaku funds, directly affects the operational efficiency. Ensure the production and operation needs of the premise, so keep inventories at a reasonable level; dynamic inventory control, timely, appropriate proposed order to avoid over storage or out of stock; reduce inventory footprint, lower total cost of inventory; control stock funds used to accelerate cash flow.Problems arising from excessive inventory: increased warehouse space andinventory storage costs, thereby increasing product costs; take a lot of liquidity, resultingin sluggish capital, not only increased the burden of payment of interest, etc., would affect the time value of money and opportunity income; finished products and raw materials caused by physical loss and intangible losses; a large number of enterprise resource idle, affecting their rational allocation and optimization; cover the production, operation of the whole process of the various contradictions and problems, is not conducive to improve the management level.Inventory is too small the resulting problems: service levels caused a decline in the profit impact of marketing and corporate reputation; production system caused by inadequate supply of raw materials or other materials, affecting the normal production process; to shorten lead times, increase the number of orders, so order (production) costs; affect the balance of production and assembly of complete sets.NotesInventory management should particularly consider the following two questions:First, according to sales plans, according to the planned production of the goods circulated in the market, we should consider where, how much storage.Second, starting from the level of service and economic benefits to determine howto ensure inventories and supplementary questions.The two problems with the inventory in the logistics process functions.In general, the inventory function:(1)to prevent interrupted. Received orders to shorten the delivery of goods fromthe time in order to ensure quality service, at the same time to prevent out of stock.(2)to ensure proper inventory levels, saving inventory costs.(3)to reduce logistics costs. Supplement with the appropriate time interval compatible with the reasonable demand of the cargo in order to reduce logistics costs, eliminate or avoid sales fluctuations.(4)ensure the production planning, smooth to eliminate or avoid sales fluctuations.(5)display function.(6)reserve. Mass storage when the price falls, reduce losses, to respond to disasters and other contingencies.About the warehouse (inventory) on what the question, we must consider the number and location. If the distribution center, it should be possible according to customer needs, set at an appropriate place; if it is stored in central places to minimize the complementary principle to the distribution centers, there is no place certain requirements. When the stock base is established, will have to take into account are stored in various locations in what commodities.库存管理库存控制在谈到所谓“库存控制”的时候，很多人将其理解为“仓储管理”，这实际上是个很大的曲解。
毕业论文摘要英文翻译
毕业论文摘要英文翻译Abstract:This paper examines the effects of exercise on mental health and well-being. As individuals continue to face increasing levels of stress and anxiety, it is important to explore alternative methods of managing and improving mental well-being. Exercise has been widely recognized as a potential solution, and numerous studies have investigated the relationship between physical activity and mental health. This research aims to synthesize and evaluate existing literature to determine the impact of exercise on mental health outcomes. The study also investigates the mechanisms through which exercise influences mental well-being.The literature review confirms the positive relationship between exercise and mental health. Regular physical activity has been shown to reduce symptoms of depression, anxiety, and stress. Furthermore, exercise is associated with improved cognitive function and increased self-esteem. Various mechanisms have been proposed to explain the beneficial effects of exercise, including the release of endorphins, increased blood flow to the brain, and social interaction.Despite the evidence supporting the positive effects of exercise on mental health, barriers exist that prevent individuals from engaging in regular physical activity. These barriers include lack of time, motivation, and access to exercise facilities. Strategies to overcome these barriers are discussed, such as incorporating exercise intodaily routines, setting realistic goals, and utilizing community resources.In conclusion, exercise has a significant positive impact on mental health and well-being. This research highlights the importance of integrating physical activity into daily life, especially in the face of increasing levels of stress and anxiety. The findings of this study provide valuable insights for individuals, healthcare providers, and policymakers. By promoting the benefits of exercise and addressing the barriers to physical activity, society can strive towards improved mental well-being for all.。
论文的英文翻译
论文的英文翻译Translation of the paper:Title: [Title of the paper]Abstract:The abstract provides a summary of the paper's main points, including the research question, methodology, results, and conclusions.1. Introduction:This section introduces the research topic, provides background information, and clearly states the research objectives. It also includes a brief literature review to highlight the relevance of the study and identify any research gaps.2. Methodology:The methodology section explains the research design, data collection methods, and analytical techniques used. It also discusses any limitations or assumptions made during the research process.3. Results:This section presents the findings of the study, including any quantitative or qualitative data collected. The results are organized in a logical and clear manner, with appropriate tables, figures, or graphs to support the findings.4. Discussion:The discussion section interprets the results, compares them toprevious research, and provides explanations for any unexpected findings. It also explores the implications and applications of the research, highlighting its contribution to the field.5. Conclusion:The conclusion summarizes the key findings of the study, restates the research objectives, and offers final thoughts on the topic. It may also suggest areas for future research or provide recommendations for practitioners.6. References:This section lists all the sources cited in the paper, following a specific citation style (e.g., APA, MLA, etc.). The references should be organized alphabetically and provide all the necessary details for readers to locate the source.Appendix:If necessary, an appendix section can be included to provide additional information that supports the main text but is not essential to the understanding of the paper. This may include raw data, lengthy tables, questionnaires, or supplementary material.。
论文翻译成英文
论文翻译成英文The Translation of the PaperWith the development of the world and rapid advancement of science and technology, the importance of communication among different countries has become increasingly prominent. This has led to a surge in demand for translation services, making translation an essential and indispensable profession.Translation is the act of conveying the meaning of a text from one language to another. It involves not only the transfer of the words, but also the ability to accurately capture the cultural nuances and context of the original text. A skilled translator must have a deep understanding of both the source and target languages, as well as a broad knowledge of various subject areas.The translation process can be divided into several stages. First, the translator needs to carefully read and comprehend the source text to fully grasp its meaning. Then, they must accurately transfer the message, while considering the characteristics and conventions of the target language. Next, the translator needs to revise and edit the translation to ensure accuracy and clarity. Finally, the completed translation should undergo rigorous proofreading to eliminate any errors or omissions.Translation plays a crucial role in numerous fields. In the business world, accurate translation of documents such as contracts, proposals, and marketing materials is essential for successful international transactions and collaborations. In the academic field, translation allows for the exchange and dissemination ofknowledge among researchers from different countries, enabling cross-cultural understanding and cooperation. In the legal field, translation of legal documents ensures that individuals from different linguistic backgrounds have equal access to justice. In the entertainment industry, translation allows for the enjoyment of foreign films, TV shows, and literature.However, translation is not as simple as replacing words from one language with their equivalents in another. Translators often face linguistic and cultural challenges that require them to make difficult decisions. They need to find equivalent expressions, idiomatic phrases, and appropriate terminology that reflect the intended meaning and cultural connotations of the original text. Additionally, the translator needs to be aware of the target audience and adapt the translation accordingly, ensuring that it is easily understood and culturally appropriate.Advancements in technology have greatly impacted the translation profession. Computer-assisted translation tools, such as translation memory software, have made the translation process more efficient and consistent. Machine translation, although still in its early stages, has shown potential for aiding human translators by providing initial drafts that can be refined. However, human translators are still irreplaceable due to their ability to understand the subtleties of language and capture the essence of a text.In conclusion, translation is a complex and multifaceted profession that plays a crucial role in facilitating communication and understanding among different cultures. It requires not only linguistic proficiency, but also cultural awareness and subjectknowledge. As the world continues to grow more interconnected, the demand for skilled translators will only continue to rise, making translation an essential skill in an increasingly globalized world.。
英语议论文经典范文3篇(带翻译)
英语议论文经典范文3篇（带翻译）有很多的同学在写英语作文的时候，也会写一些经典的议论文，小编整理了相关范文，希望会对大家有所帮助！英语作文范文带中文翻译Manyyearsago,themovieabouttheyouthbecameverypopular,everyyear,wecanseeman yhotmoviesabouttheprotagonist’spassedyouth.Peopleliketorecalltheirpassedyouth, whichmakessuchmoviessellgood.ButIfindthecommonthingsaboutthesemovies,alltheprotagonists’youthareaboutfighting,loveandothernegativethings.Iunderstandthedirectors’intention,theywanttotellpeopleyouthisnotperfectandhavingpities.Ofcourse movieisexaggerating,therealyouthisaboutstudying,atleast,mostpeoplehaveworkedso hardtogetintotheiridealcolleges.Whatthemoviesdescribemakeupsomepeople’syouth,forwhichtheydon’thavethechancetoexperience.Weshouldnotbemisledbythesemovies,fortheteenagers,theirjobistostudy,sothattheycanhaveabrightfuture.【翻译】很多年以前，关于青春的电影很受欢迎，此后每年，我们都可以看到很多热门电影是关于主人公逝去的青春。
论文英文摘要翻译
论文英文摘要翻译AbstractThe rapid development of technology has greatly affected various industries, including the education sector. E-learning, as a form of remote education, has gained popularity in recent years. This paper aims to investigate the impact of e-learning on students' learning outcomes and motivation.To achieve this objective, a literature review was conducted to identify the relevant research on e-learning and its effects. The findings show that e-learning has positive effects on students' learning outcomes, such as increased knowledge acquisition and self-directed learning skills. E-learning provides a flexible learning environment, allowing students to access educational resources anytime and anywhere. This convenience enhances students' motivation and engagement in learning activities.However, the effectiveness of e-learning depends on various factors. The quality of the e-learning platform and instructional design plays a crucial role in engaging students and promoting effective learning. In addition, the role of teachers in facilitating e-learning is also important. Teachers' guidance and support are essential in helping students navigate the online learning platform and clarify any doubts.Moreover, the digital divide is a significant challenge in implementing e-learning. Not all students have access to reliable internet connection and necessary technological devices. Therefore, it is crucial to bridge the digital divide to ensure equalopportunities in e-learning.Furthermore, challenges such as limited social interaction and a lack of personalized feedback in e-learning need to be addressed. Efforts should be made to incorporate interactive features and provide timely feedback to promote effective learning and address students' individual needs.In conclusion, e-learning has the potential to positively impact students' learning outcomes and motivation. However, it is crucial to address challenges related to technological infrastructure, instructional design, and teacher support to maximize the benefits of e-learning. Future research should focus on exploring effective strategies for integrating e-learning into traditional educational settings to create a blended learning approach.Keywords: e-learning, learning outcomes, motivation, instructional design, teacher support。
论文英文翻译
论文英文翻译Essay 1 - College EducationIn recent years, college education has become a topic of great debate. Some people argue that a college degree is essential for success in today's society, while others believe that it is not necessary. This essay will argue that college education is indeed important and beneficial for several reasons.Firstly, obtaining a college degree can provide individuals with better career opportunities. In today's competitive job market, employers often prioritize candidates with a higher education background. College graduates are more likely to find stable employment and earn higher salaries compared to those without a degree. Furthermore, many professions require specific knowledge and skills that can only be acquired through a college education. For example, doctors, engineers, and lawyers must complete several years of study in order to obtain the necessary qualifications for their respective fields.Secondly, college education can help individuals develop important life skills. During their time at college, students are exposed to a variety of subjects and experiences, which enable them to develop critical thinking, problem-solving, and communication skills. College also provides opportunities for students to engage in extracurricular activities and interact with a diverse group of individuals. This fosters social and cultural awareness, as well as teamwork and leadership skills. These skills are valuable not only in the workplace but also in everyday life.Moreover, college education promotes personal growth and lifelong learning. The college environment encourages students to explore new ideas, challenge their assumptions, and discover their passions. It provides a platform for intellectual development and self-discovery. Students are exposed to a wide range of subjects, perspectives, and cultures, which broadens their knowledge and worldview. College education also instills a sense of curiosity and a desire for continuous learning, which are essential qualities in today's rapidly changing world.In conclusion, college education is important and beneficial for several reasons. It provides better career opportunities, helps individuals develop important life skills, and promotes personal growth and lifelong learning. While it is true that college education may not be necessary for everyone, obtaining a degree can significantly enhance one's chances of success in both personal and professional aspects of life.。
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毕业设计（论文）英文文献翻译电力系统电力系统介绍随着电力工业的增长，与用于生成和处理当今大规模电能消费的电力生产、传输、分配系统相关的经济、工程问题也随之增多。
这些系统构成了一个完整的电力系统。
应该着重提到的是生成电能的工业，它与众不同之处在于其产品应按顾客要求即需即用。
生成电的能源以煤、石油，或水库和湖泊中水的形式储存起来，以备将来所有需。
但这并不会降低用户对发电机容量的需求。
显然，对电力系统而言服务的连续性至关重要。
没有哪种服务能完全避免可能出现的失误，而系统的成本明显依赖于其稳定性。
因此，必须在稳定性与成本之间找到平衡点，而最终的选择应是负载大小、特点、可能出现中断的原因、用户要求等的综合体现。
然而，网络可靠性的增加是通过应用一定数量的生成单元和在发电站港湾各分区间以及在国内、国际电网传输线路中使用自动断路器得以实现的。
事实上大型系统包括众多的发电站和由高容量传输线路连接的负载。
这样，在不中断总体服务的前提下可以停止单个发电单元或一套输电线路的运作。
当今生成和传输电力最普遍的系统是三相系统。
相对于其他交流系统而言，它具有简便、节能的优点。
尤其是在特定导体间电压、传输功率、传输距离和线耗的情况下，三相系统所需铜或铝仅为单相系统的75%。
三相系统另一个重要优点是三相电机比单相电机效率更高。
大规模电力生产的能源有：1.从常规燃料（煤、石油或天然气）、城市废料燃烧或核燃料应用中得到的蒸汽；2.水；3.石油中的柴油动力。
其他可能的能源有太阳能、风能、潮汐能等，但没有一种超越了试点发电站阶段。
在大型蒸汽发电站中，蒸汽中的热能通过涡轮轮转换为功。
涡轮必须包括安装在轴承上并封闭于汽缸中的轴或转子。
转子由汽缸四周喷嘴喷射出的蒸汽流带动而平衡地转动。
蒸汽流撞击轴上的叶片。
中央电站采用冷凝涡轮，即蒸汽在离开涡轮后会通过一冷凝器。
冷凝器通过其导管中大量冷水的循环来达到冷凝的效果，从而提高蒸汽的膨胀率、后继效率及涡轮的输出功率。
而涡轮则直接与大型发电机相连。
涡轮中的蒸汽具有能动性。
蒸汽进入涡轮时压力较高、体积较小，而离开时却压力较低、体积较大。
蒸汽是由锅炉中的热水生成的。
普通的锅炉有燃烧燃料的炉膛燃烧时产生的热被传导至金属炉壁来生成与炉体内压力相等的蒸汽。
在核电站中，蒸汽的生成是在反应堆的帮助下完成的。
反应堆中受控制的铀或盥的裂变可提供使水激化所必需的热量，即反应堆代替了常规电站的蒸汽机。
水电站是利用蕴藏在消遣的能来发电的。
为了将这种能转换为功，我们使用了水轮机。
现代水轮机可分为两类：脉冲式和压力式（又称反应式）。
前者用于重要设备，佩尔顿轮是唯一的类型；对于后者而言，弗朗西斯涡轮或其改进型被广泛采用。
在脉冲式涡轮中，整个水头在到达叶轮前都被转化为动能，因为水是通过喷嘴提供给叶轮的；而在压力式或反应式涡轮中，水通过其四周一系列引导叶版先直接导入叶片再提供给叶轮（或转子）。
离开引导叶片的水有压力，并且以一部分动能、一部分压力的形式来提供能量。
对于低于10,000千伏安的发电站而言柴油机是出色的原动机。
其优点是燃料成本低、预热时间短以及标准损耗低。
此外，其所需冷却水量极少。
柴油发电通常选择用于满足少量电力需求，如市政当局、宾馆及工厂等；医院通常备有独立的柴油发电机，以备紧急情况时使用。
通过电线来传输电能是电力系统中的一个重大问题。
而从下面研修目的目的架设输电线路又是必要的：1.将电力从水电站输送到可能很远的负载中心；2.从蒸汽站到相对较近负载中心电力的批量供应；3.出于内部连接目的将电能在紧急情况下从一系统转换至另一系统。
传输电压主要由经济因素决定。
实际上，当距离、功率、功耗固定时，输电线路中导体的重量与传输电压成反比。
因此，出于经济方面的考虑，长距离传输时电压一定要高。
当然，电压超高绝缘成本也就超高，要找到最佳电压必须通过减小导体横截面积来取得绝缘成本与经济节省之间的平衡。
高压传输通常使用配以悬挂式绝缘设备的高架结构。
称为路标铁塔用于负载绝缘设备，各导体悬挂于一组或一串绝缘体的底部。
最常用的导体类型如下：多芯铜导线、空心铜导线和ACSR（用钢加强的铝线）导线。
电力分配系统包括由高夺线供能的子电站与用户开关之间的所有部件。
电力从子电站接收，并以电压标准按不同类型用户均能接受的持续程度分送到各用户。
在大城市中，高架与地下布线方式均被采用。
尽管地下布线方式比高架方式昂贵，但在高度城市化地区却必不可少。
而在小城镇和较疏散的大城市区域，整个分配系统通常都是高架式的。
电力系统监控现代电力系统都是由许多部分组成的统一体，而每个部分又都影响着其他部分的特性。
为了整个系统能正常运行，就必须在系统的许多不同地点监控其工作情况以确保系统处于最佳工作状态。
用户方根关心的是供电频率和电压的变化范围要小。
既然系统内的频率在任何地方都是相同的，因而只要在便于观测之处安装一个频率表就能进行监控与此相反，系统的电压在不同的测试点上会有很大的差别。
因此，有必要在系统的某些关键测点上对电压进行不断的观测，以便提供满意的服务。
给系统内每台发电机规定适当的负荷时间访问演出能使系统有效地运行。
纵然一些新的电厂各自都有较高的效率，但是由于设置地点不当，可能产生巨大的系统电能损失。
发电机之间的负荷分配应使总的燃料费用最小。
要在任何意相不到的情况下保证正常供电，所有发电机的总额定功率就必须略大于总负荷加上损耗值。
这种富余电量通称为旋转备用容量，它可以弥补用户突然增加的负荷或某台发电机因需要检修而突然甩掉的负荷。
为了向用户征收电费，就必须安装电表。
在不同的电力系统之间有许多联结线。
仪表必须安装在联接点上，以便记录从一个系统传输到另一个系统的电能。
这种监测要连续进行，以确保相互输送的电力在合同允许的限度之内。
为防止过截造成的损坏，有必要对各个主要设备的工作状态进行不断的监测。
由于负载逐月增加，需要增加设备容量的地点是可以查明的，附加设备的安装就有可能得到保障。
因此，在日益扩大的电力系统的未来建设中，检测仪表起着指南的作用。
有时，在紧急情况下，系统操作人员观测到时他的系统负荷超过了发电能力和输电能力。
那么他就面临着甩掉部分负荷或者确切地说保持负荷不变这样的问题因而就有必要在中断供电造成损失最小的地区有选择地甩掉负荷。
在这种情况下，系统操作人员依靠许许多多仪表进行工作。
这些仪表显示着系统运行情况的信息。
当设备的运行走出其设计极限时，仪表可以发出警报声，作为要求采取避免设备损坏的行动的预告。
在出现像电力系统发生故障这种极端不利的情况时，有毛病的设备就会自动停止运行。
监控电流、电压和其他指标的仪表必须能识别有故障的设备，并使断路器开始工作，让有故障的设备停止运行，而让运行系统中的其余设备仍继续工作。
电力系统上的那些众多而不同的电气设备和用户拥有的那些电气设备都是按照在特定范围内运行而设计的。
凡超出这些设计限度的运行都是不合适的，因为这可能导致运行效率很低、能量损耗很多或者（在极端的情况下）使设备毁坏。
仔细观察设备的运行情况就可以发现需要采取的修正措施。
各种电气设备都不应该出现过量电流，因为它会产生过高的温度使运行效率降低而缩短设备的使用寿命。
居民区电路上出现过量电流时，由于保险丝和电闸的作用会造成电路中断。
马达内的过量电流有可能损坏绝缘而过早出现绝缘故障。
电压不足会极大地降低白炽灯泡的亮度，并可能使荧光灯不发光。
供电电压过低会在马达内造成过量电流而有可能损坏马达的线圈。
电压过高提高了灯泡的发光亮度，但是在许多情况下会严重缩短灯泡的使用寿命。
给马达和变压器超夺供电能在绕组铁芯里产生过多的能量损失，有可能使保持铁芯或绕组线圈的绝缘遭到损坏。
机器的超速旋转有可能对机器的转动部件造成结构上的损坏。
用户生产设备的超速运行可能造成劣质产品。
在两台发电机或一台发电机与一台同步马达之间存在的不协调状态会导致这两台机器有效功率传输的中断。
不协调状态应立即查明，两台机器也应立即分开。
然后，才可以使它们恢复同步继续运行。
在电力系统的许多工作位置上和许多用户的家中都要安装许多各种型号的仪表。
有了这些仪表，就能连续监控供电的工作状态。
Electric Power SystemsIntroduction of Electric Power SystemsAs the power industry grows, so do the economic and engineering problems connected with the generating, transmission and distribution systems used to produce and handle the vast quantities of electrical energy consumed today. These systems together form an electrical power system.It is important to note that the industry that produces electrical energy is unique in that it manufactures its product at the very instant that it is required by the customer. Energy for the generation of electricity can be stored in the form of coal and oil, and of water in reservoirs and lakes, to meet future requirements, but this does not decrease the need for generator capacity to meet the customers’ demands.It is obvious that the problem of the continuity of service is very important for an electrical power system. No service can be completely protected from the possibility of failure and clearly the cost of the system will depend on its requirements. However a net reliability gain is obtained by employing a certain number of generating unitsand by using automatic breakers for the separation into sections of the bus bars in generating stations and of the transmission lines in a national or international grid system. In fact a large system comprises numerous generating stations and loads interconnected by high-capacity transmission lines. An individual unit of generation or set of transmission ‘lines can usually cease to function without interrupting the general service.The most usual system today for generation and for the general transmission of power is the three-phase system. In favor of this system are its simplicity and its simplicity and its saving with respect to other a.c. system. In particular, for a given voltage between conductors, with a given power transmitted, with a given distance, and with a give line loss, the three-phase system requires only 75 per cent of the copper or aluminium needed in the single-phase system. Another important advantage of the three-phase system is that three-phase motors are more efficient than single-phase ones. The sources of energy ofr large-scale electricity generation are:1.steam obtained by means of a conventional fuel (coal, oil or natural gas),the combustion of city refuse or the employment of nuclear fuel;2.water;3.diesel power from oil.There are other possible sources of energy such as direct solar heat, wind power, tidal power, etc., but none of these has yet gone beyond the pilot-plant stage.In large steam power plants, the thermal energy stored in steam is converted into work by means of turbines. A turbine consists essentially of a shaft or rotor fixed in bearings and enclosed in a cylindrical casing. The rotor is made to turn smoothly by means of jets of steam from nozzles around the periphery of the turbine cylinder. These steam jets strike blades attached to the shaft. Central power stations employ condensing turbines in which the steam passes into a condenser after leaving the turbine. Condensation is effected by the circulation of large quantities of cold water through the tubes of the condenser,thus increasing the expansion ratio of the steam and the consequent efficiency and work output of the turbine. The turbines are connected directly to large electricity generators.In turbines the action of the steam is kinetic. There is progressive expansion of the steam from the high pressure and relatively small volume at which it leaves.Steam is made by heating water in a boiler. The usual boiler has a furnace in which fuel is burned, and the heat given off during combustion is conducted through the metal walls of the boiler to generate steam at a pressure within the boiler vessel. In nuclear plants, steam is generated with the aid of a reactor in which the controlled fission of uranium or plutonium supplies the necessary heat for the vaporization of water. Thus the reactor rep; aces the steam generator of conventional plants.Use is made of the energy possessed by water in hydroelectric stations. In order to transform this energy into work, hydraulic turbines are used. Modern hydraulic turbines may be divided into two classes: impulse turbines and pressure or reaction turbines. Of the former, the Pelton wheel is the only type used in important installations; of the latter, the Francis turbine or one of its modifications is universally employed.In an impulse turbine, the whole head of water is converted into kinetic energy before the wheel is reached, as the water is supplied to the wheel through a nozzle. In the pressure or reaction turbine the wheel (or runner) is provided with vanes into which water is directed by means of a series of guide vanes around the whole periphery. The water leaving these guide vanes is under pressure and supplies energy partly in the kinetic form and partly in the pressure form.The diesel engine is an excellent prime mover for electricity generation in plant below about 10,000 KV A. It has the advantage of low fuel cost, a brief warming-up period and low standing losses. Moreover it requires little cooling water. Diesel generation is generally chosen for small power requirements by municipalities, hotels and factories; hospitals often keep and independent diesel generator for emergency supply.The transmission of electrical energy by means of lines is a great problem in electrical power systems. Transmission lines are essential for three purposes:1.To transmit power from a hydroelectric site to a load center perhaps aconsiderable distance away;2.For the bulk supply of power from steam stations to load centers arelatively short distance away;3.For interconnection purposes to transfer energy from one system toanother in case of emergency.The transmission voltage is determined largely by economic factors. In fact, in a transmission line, if the distance, the power and the power loss are fixed, the total weight of the conductor varies inversely as the square of the transmission voltage. For the economic transmission of power over considerable distances the voltage must therefore be high. Naturally with higher voltages the insulation cost also rises and to find the optimum voltage we must strike a balance between this cost and the saving through the reduction of the cross-section of the conductors.For high voltages, overhead-line construction is generally used with suspension-type insulators. Steel tower, called pylons serve to carry the insulators, with each conductor suspended from the bottom of a group or string of insulator units. The following types of conductor are those most commonly used: stranded copper conductors, hollow copper conductors and ACSR (aluminum cable, steel reinforced) conductors.Distribution includes all the parts of the electricity system between the power substations supplied from high-voltage transmission lines and the consumer’s switch. Electric power is received from substations and distributed to the consumers at the voltage levels and with the degree of continuity that are acceptable to the various types of consumer. In large metropolitan systems both over head and underground distribution methods are used. Although underground distribution is more expensive than an overhead system, it is virtually a necessary in heavily urbanized areas. In smaller towns and in the less congested districts of large cities, the entire distribution system is usually overhead.Electric System MonitoringA modern electric power system is an assembly of many components each of which influences the behavior of every other part. Proper functioning of the system as a whole makes it necessary to monitor conditions existion at many different points on the system in order to assure optimum operation.The concern of the customers is primarily that the frequency and voltage of the supply are held within certain rather narrow limits. Since frequency of the system is the same everywhere, it may be monitored by a single frequency meter located at any convenient point. In contrast the voltage of the system may be quite different at different points. Consequently, it is necessary to make continuous observation of the voltage at certain key points on the system in order to provide acceptable service.Efficient operation of the system is obtained by assigning proper load schedules to each of the generators on the system. Newer plants, although individually more efficient, may be located at points on the system where their loading occasions large system losses. It is desirable to operate with a division of the load between generators so that the total cost of fuel consumed is minimized. To provide reliability of the power supply in tile event of unexpected conditions, it is desirable to have the total kilowatt rating of all machines in operation somewhat greater than the total load plus losses. This excess of generation, known as spinning reserve, is then available for picking up suddenly applied customer loads or to pick up the load dropped by a generator that must be removed from service for emergency maintenance.Instrumentation is necessary to permit billing of Customers for energy used. Many interconnections exist between different power systems. Instruments must be provided at interchange points to permit billing for energy transferred from one system to another. The continuous monitoring of energy transfer is necessary to assure that interchanged power is within the limits of contract agreements.The continuous measurement of conditions on major pieces of equipment is necessary to avoid damage due to overload. As load increases from month to month, points at which additional capacity of equipment is required may be recognized and provision made for the installation of additional equipment. Thus instrumentation serves as a guide for future construction in a growing power system.Occasionally, under emergency conditions, a system operator observes that his system load exceeds the ability of the available generating and transmission equipment. He is then faced with the problem of load shedding or ,more properly, load conservation. It is then necessary to drop selected loads where service interruption is least objectionable. In such an event, he relies on the many instruments which provide information relative to system-operation conditions.Instruments may sound alarms as advance warnings of conditions requiring action to avoid damage to equipment operating beyond its design limitation. In the event of extreme conditions such as power-system faults, defective equipment is switched out of service automatically. Instruments that continuously monitor current voltage, and other quantities must be able to identify the faulted equipment and to bring about operation of the circuit breakers which remove it from service, while leaving in service all other equipment on the operating system.The many different electrical devices on a power system and those owned by thecustomers are designed for operation within certain specified ranges. Operation, excessive deterioration, or (in extreme cases ) the destruction of the device. Careful attention to the conditions under which equipment is operating may indicate corrective action that must be taken.Overcurrent on all electrical devices is undesirable, as it produces excessive temperatures, inefficient operation, and reduced service life. Overcurrent in residential circuits may bring about disconnection of the circuit by fuse or breaker action. Overcurrent in motors may damage insulation, with possible early insulation failure.Undervoltage considerably reduces the efficiency of incandescent lamps and may result in nonoperation of fluorescent lamps. Undervoltage of the power supply to motors may result in excessive currents in the motors, with possible damage to windings.Overvoltage increases the light output of lamps but in many instances seriously shortens useful life. Overvoltage applied to motors and transformers may result in excessive losses within the iron, with possible damage to the iron or to the adjacent winding insulation.Overspeed of rotating machines may result in structural damage to rotating parts. The overspeed of the customers’production equipment may result in an inferior quality of the product.An out-of-step condition existing between two generators or between a generator and a synchronous motor results in an interruption of useful power transfer between the two machines. An out-of-step condition should be recognized promptly and the machines separated from each other. They may then be resynchronized and brought back into service.Instruments of many different types must be installed at many locations on a power system and on the premises of the many customers. With such instruments, conditions existing on the system may be continuously monitored.。