电力系统继电保护外文及翻译演示教学

电力系统继电保护外

文及翻译

Power System Protections

The steady-state operation of a power system is frequently disturbed by various faults on electrical equipment. To maintain the proper operation of the power system, an effective, efficient and reliable protection scheme is required. Power system components are designed to operate under normal operating conditions.However, due to any reason, say a fault, there is an abnormality, it is necessary that there should be a device which senses these abnormal conditions and if so, the element or component where such an abnormality has taken place is removed, i.e. deleted from the rest of the system as soon as possible. This is necessary because the power system component can never be designed to withstand the worst possible conditions due to the fact that this will make the whole system highly uneconomical. And therefore, if such an abnormality takes place in any element or component of the power system network, it is desirable that the affected element/component is removed from the rest of the system reliably and quickly in order to restore power in the remaining system under the normal condition as soon as possible.

The protection scheme includes both the protective relays and switching circuits, i.e. circuit breakers. The protective relay which functions as a brain is a very important component. The protective relay is a sensing device, which senses the fault, determines its location and then sends command to the proper circuit breaker by closing its trip coil. The circuit breaker after getting command from the protective relay disconnects only the faulted element. this is why the protective relay must be reliable, maintainable and fast in operation.

In early days, there used to be electromechanical relay of induction disk-

type.However, very soon the disk was replaced by inverted cup, i.e.hollow cylinder and the new relay obtained was known as an induction cup or induction cylinder relay. This relay, which is still in use, possesses several important features such as higher speed; higher torque for a given power input an more uniform torque.

However, with the advent of electronic tubes, electronic relays having distinct features were developed during 1940s. With the discovery of solid state components during 1950s, static relays with numerous advantages were developed. The use of digital computers for protective relaying purposes has been engaging the attention of research and practicing engineers since layer 1960s and 1980s. Now, the microprocessor/mini computer-based relaying scheme, because of its numerous advantages such as self –checking feature and flexibility, has been widely used in power system all over the world.

The overall system protection is divided into following sections: (i)Generator protection,(ii)Transformer protection,(iii)Bus protection,(iv)Feeder

protection,(v)Transmission line protection.

Basic Requirements to Protective Relays

Any protection scheme, which i.e. required to safeguard the power system components against abnormal conditions such as faults, consists basically of two elements(i)Protective relay and (ii) Circuit breaker .The protective relay which is primarily the brain behind the whole scheme plays a very important role. Therefore proper care should be taken in selecting an appropriate protective relay which is reliable, efficient and fast in operation. The protective relay must satisfy the following requirements:

⑴ since faults on a well designed and healthy system are normally rare, the

relays are called upon to operate only occasionally. This means that the

relaying scheme is normally idle and must operate whenever fault occurs. In

other words, it must be reliable.

⑵ Since the reliability partly depends upon the maintenance, the relay must

be easily maintainable.

⑶ The palpation of the relay can be in two ways. One is the failure to operate

in case a fault occurs an second is the relay operation when there is no fault.

As a matter of fact, relay must operate if there is a fault and must not

operate if there is no fault.

⑷Relaying scheme must be sensitive enough to distinguish between normal

and the faulty system.

Protective Relays

The function of the protective relay is to sense the fault and energize the trip

coil of the circuit breaker. The following types of the protective relays are used

for the apparatus such as synchronous machines, bus bar, transformer and the

other apparatus and transmission line protection.

(1) Over current relays,

(2) Under voltage relays,

(3) Under frequency relays,

(4) Directional relays,

(5) Thermal relays,

(6) Phase sequence relays such as(i)negative sequence relays and, (ii)zero

sequence relays,

(7) Differential relays and percentage differential relays,

(8) Distance relays such as (I)plane impedance relays,(ii)angle impedance relay,

i.e. Ohm or reactance relays,(iii)angle admittance relays,i.e. Mho relays

and ,(iv)offset and restricted relays,

(9)Pilot relays such as (i) wire pilot relays,(ii)carrier channel pilot

relays,(iii)microwave pilot relays. There are different types of the relaying

scheme based on construction. They are:(i)electromechanical

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外文翻译范例

要求：选择一篇和自己论文或者自己专业相关的外文进行翻译，英文字符数在6000-7000字符（注：可以继续按原文的一部分）。排版格式按照下文公司的核心竞争力原文来源：The Core Competence of the Corporation, Research Report on Harvard Business Review,1990 至少有三种检验方法可以用来确定公司的核心竞争力。首先，核心竞争力能够为公司进入多个市场提供方便。举例来说，显示器系统方面的核心竞争力能够使一家公司涉足计算器、微型电视机、手提电脑显示屏以及汽车仪表盘等广泛的业务领域，这就是卡西欧公司进军手持式电视机市场不足为奇的原因。第二，核心竞争力应当对最终产品为客户带来的可感知价值有重大贡献。显然，本田公司的发动机专长满足了这个条件。最后一点，核心竞争力应当是竞争对手难以模仿的。如果核心竞争力是各项技术和生产技能的复杂的融合，那么这项能力就难以被竞争对手模仿。竞争对手或许能够获得核心竞争力中的几种技术，但是要复制其内部协调与学习的整体模式却非常困难。在20世纪60年代初期，JVC决定致力于录像带技术方面的核心竞争力，这个核心竞争力就通过了我们上述的三项检验。20世纪70年代末美国的RCA公司决心开发以唱针为基础的视频转动式系统，这个项目则不能通过上述三项检验。。。。。。。。。。。。 The Core Competence of the Corporation The Core Competence of the Corporation Research Report on Harvard Business Review,1990 The distinction we observed in the way NEC and GTE conceived of themselves a portfolio of competencies versus a portfolio of businesses was repeated across many industries. From 1980 to 1988, Canon grew by 264%, Honda by 200%. Compare that with Xerox and Chrysler. And if Western managers were once anxious about the low cost and high quality of Japanese imports, they are now overwhelmed by the pace at which Japanese rivals are inventing new markets, creating new products, and enhancing them. Canon has given us personal copiers; Honda has moved from motorcycles to four wheel off road buggies. Sony developed the 8mm camcorder, Yamaha, the digital piano. Komatsu developed an underwater remote controlled bulldozer, while Casio's latest gambit is a small screen color LCD television. Who would have anticipated the evolution of these vanguard markets? In more established markets, the Japanese challenge has been just as disquieting. Japanese companies are generating a blizzard of features and functional enhancements that bring technological sophistication to everyday products. Japanese car producers have been pioneering four wheel steering, four valve-per cylinder engines, in car navigation systems, and sophisticated

外文翻译--农村金融主流的非正规金融机构

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电力系统继电保护外文翻译

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关于商业银行信用风险的文献综述

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外文翻译模板

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3英文文献及翻译格式示例

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The electrical power system rapid development to the relay protection propose unceasingly the new request, the electronic technology, computer technology and the communication rapid development unceasingly has poured into the new vigor for the relay protection technology development, therefore, the relay protection technology is advantageous, has completed the development 4 historical stage in more than 40 years time. After the founding of the nation, our country relay protection discipline, the relay protection design, the relay manufacture industry and the relay protection technical team grows out of nothing, has passed through the path in about 10 years which advanced countries half century passes through. The 50's, our country engineers and technicians creatively absorption, the digestion, have grasped the overseas advanced relay protection equipment performance and the movement technology , completed to have the deep relay protection theory attainments and the rich movement experience relay protection technical team, and grew the instruction function to the national relay protection technical team's establishment. The relay factory introduction has digested at that time the overseas advanced relay manufacture technology, has established our country relay manufacturing industry. Thus our country has completed the relay protection research, the design, the manufacture, the movement and the teaching complete system in the 60's. This is a time which the mechanical and electrical relay protection prospers, was our countries relay protection technology development has laid the solid foundation. From the end of the 50's, the transistor relay protection was starting to study. In the 60's to the 80's，it is the times which the transistor relay protection vigorous development and widely used. Tianjin University and the Nanjing electric power automation plant cooperation research 500kV transistor direction high frequency protection the transistor high frequency block system which develops with the Nanjing electric power automation research institute is away from the protection, moves on the Gezhou Dam 500kV line , finished the 500kV line protection to depend upon completely from the overseas import time. - 2 -

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with knowledge management. Finally, the paper studies ways for banks to manage credit risks with knowledge management. With the application of knowledge management in financial banks, customers will acquire better service and banks will acquire more rewards. Index Terms–knowledge management; credit risk; risk management; incentive mechanism; financial banks I.INTRODUCTION Nowadays,banks are operating in a“knowledge society”.So, what is knowledge? Davenport(1996)[1]thinks knowledge is professional intellect, such as know-what, know-how, know-why, and self-motivated creativity, or experience, concepts, values, beliefs and ways of working that can be shared and communicated. The awareness of the importance of knowledge results in the critical issue of “knowledge management”. So, what is knowledge management? According to Malhothra(2001)[2], knowledge management(KM)caters to the critical issues of organizational adaptation, survival and competence in face of increasingly discontinuous environmental change. Essentially it embodies organizational processes that seek synergistic combination of data and information processing capacity of information technologies and the creative and innovative capacity of human beings. Through the processes of creating,sustaining, applying, sharing and renewing knowledge, we can enhance organizational performance and create value. Many dissertations have studied knowledge managementapplications in some special fields. Aybübe Aurum(2004)[3] analyzes knowledge management in software engineering and D.J.Harvey＆R.Holdsworth(2005)[4]study knowledge management in the aerospace industry. Li Yang(2007)[5] studies knowledge management in information-based education and Jayasundara＆Chaminda Chiran(2008)[6] review the prevailing literature on knowledge management in banking industries. Liang ping and Wu Kebao(2010)[7]study the incentive mechanism of knowledge management in Banking. There are also many papers about risks analysis and risks management. Before the 1980s, the dominant mathematical theory of risks analysis was to describe a pair of random vectors.But,the simplification assumptions and methods used by classical competing risks

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