电气工程及其自动化本科毕业设计(论文)中英文对照翻译-电力系统
本科毕业设计（论文）
电气工程及其自动化本科毕业设计（论文）中英文对照
翻译-电力系统
电力系统
1 电力的技术特点
电力具有独特的技术特点，这使得电力工业具有独特的行业特点。
1.无形性。用户不能用人体感官直接察觉千瓦时的用电量。
2.质量。供电质量可由供电连续性或供电可靠性、在标准电压等级下的电压均等性、交流电压频率的正确不变性来度量。
3.电力的贮存。与大多数行业不同，电力部门必须随时根据用电的需求生产出电力来，因为电能无法贮存。
4.对供电负责。电由电力部门输送到用户，因此必须对安全、可靠供电负责。
5.对公众的安全。电力部门须对公众及其技术人员提供稳妥的保护。
2 电力系统的规划
预期到电力部门的供电负荷将持续增长，电力系统的容量也持续增大。远期规划主要是保证这种扩建在技术上是适宜的，在造价上是合理的，与增长模式是相符的。远期规划者碰到的困难包括：不同地域和不同时间负荷增长的不确定性、新发明新技术发展的可能性。优异的系统规划要努力做到全系统设计的最优化，而不能为了系统某部分造价的最小化而不顾其它部分的影响。近年来，已经强调了规划和运行的经济性。现在则越来越强调可靠性和环境方面的因素。
在作出规划前，须要仔细考虑许多因素：
（1）设备的决策具有远期效应，这需要15—25年的预期和研究。
（2）有许多发电途径可选择：核电、基荷火电、中等规模燃气轮机发电或水电，以及大型、中型、小型电厂和各种形式的蓄能。
（3）有多种送电途径可选择，例如由交流或直流，架空线或地下电缆送电并有各种电压等级。
（4）规划决策受负荷管理技术和负荷模式的影响。
（5）有关因素存在不确定性。如将来燃料价格货币的利率资金的来源设备的强迫停运率新技术环境的要求。
3 电力分配
3.1 最初的分配系统
发电厂和最后的各支路之间的分配线路叫做最初的分配系统。在这两个电力系统之间传输有多种方法. 其中最常见的两种方法是辐射式和环绕式。
（1）.辐射式
这种辐射来自于全世界的辐射，意思就是从中心向四周扩散。这种辐射系统是一类起源于主电站并向各种分电站传递电能的电力传输系统。从最简单的出发, 一个辐射系统是从生产电能的发电厂辐射开来. 这些电能从主电站被传输出来，通常是部分的，或者是从相邻的发电厂发出的. 所以从主电站输出的电能为了长距离输电，在主电站将电压升高到较高的值。
从主电站,许多线路将电能传达到各地方的电站. 为了在人口密集地区配电，在分电站将电压降低到合适的值。在分电站,电能是通过线路传输给各变压器的。这些变压器再把电压降低到能让用电户所承受的电压。（2）环系统
环系统是从主电站或者一个分电站开始而且经过周围变电站电能的相互传输最后回到主电站的。这将造成所有的电站供应同样的电能,最后因为隔离绝缘而崩溃。所以环系统的维持需要一个更大的环系统并从主电站供电。
（3）用户分配系统
不同的用户分配系统是用户根据自己的用电量向输电线路要电的。普通用户通常是使用最简单的类型。而商业的和工业的系统大多数因负荷需求而改变.
3.2 单相系统
大多数的单相系统是由一个最初的三向系统提供的。单相变压器被连接到三向系统中。副边包含两个带中间接点的两个串联连接线圈以够成单相三线系统。这种连接方式通常是用来向用户和一些商业用户而建立的。
对于普通住宅用户,供电通常是在头顶或地下安装.单个用户通常把电表安装在住宅外面。从电表我们可以看到每户的用电量。三个分离系统来自于每个环流系统。
从分离系统中,供电单位通过操纵台给部门提供电能。因为普通用户有三个基本的线路: 一般的照明线路，小型的机械和洗衣店线路,个体分支线路. 个体分支线路时常用来供应中央暖气系统及空调系统，水加热器和其他的特别负荷。
（1）接地需求
所有的交流电路系统都需要单相接地。这种接地系统运行制度意味着六个交流回路互相不干扰。一个接地装置的型号来源于整个接地系统的配置。
（2）商业的和工业的接地装置
商业的和工业的接地装置的安装超过小的住宅安装。大的公寓或者楼房，虽然分散了住宅的空间,但是经常使用商业广告-风格来布置。单相变压器，三绕组变压器或三相变压器都可能用于建筑物之内, 通常埋入地下.通常这些主变压器是用来供应电能的。从这点来说，供电系统为每个用户连接分别连接电表是为了保护用电户的权益。每个操纵台安装一个电表用来监视用电单位。使用这种方式是为了根据用户的数量，商业或者工业建筑可能不止一个电表。通常是一个三相或者四相电路的系统.这种电压可能是120/208 伏或277/480 伏。如果系统提供277/480 伏的电压, 那么一个变压器一定是被安装在里面为了要获得120伏的电压。如果建筑物包括一个很大的区域,那么电表一定安装在它的附近。这样安排是为了在传输线上将线路电流损失减到最少. 一些公共的电能是从一个单相变压器，三绕组变压器或三相变压器系统供应的。可能从三绕组变压器或三相变压器系统通常获得的电压是240伏，440伏或550伏.这样安排, 是为了使一个变压器获得120伏的电压. 通常从四线出来的是240伏的电压，三相变压器的电压是120伏。
许多用户购买电都是从最初的供电局买来的。通常使用15千伏三相
变压器。
这种管理电能的金属小屋叫分电局. 变压器在里面是与其他装置相邻安装的。这种抽屉类型的隔绝开关安装在分电局里。这些开关用来在维护或修理期间隔离来自补给的主要开关或线路断路器.
3.3 用户环绕式系统
虽然辐射状的变电站系统普遍存在于各级输电线路上，但大多数用户也可以接受来自环状系统的供电网络。
当安装任何系统的供电网络时,你都要考虑是否合适最初的用电需求。设计和安装人员操作这些系统一定要遵从NEC 的要求和当地的需求.
3.4 中级的高电压分配系统
大型的工厂建立地点可能找在电压比600伏高而且经济的地方。基于安装类型和负载需要，可以采用高达2300伏的电压。降压变压器在降低成本和消耗上体现了价值。
有时高电压系统可能是辐射式的,低电压系统可能进入系统之内被连接。另外的一个方法是将两种系统连接起来使用。
（1）二次环绕系统
大多数情况下在变压器之间用点把不同的负荷连结到系统中也是很方便的.这种系统叫做二次环绕系统. NEC450 型号的设备给出了特殊的关于最终级的环绕系统。
（2）接地系统
一般地说, 大多数的电力系统都要置于地面.。放在地面上的目的是将限制由闪电而发出瞬间的励磁涌流和的意外接触较高的电压所引起的过电压。当接地故障发生时，为保证过流设备工作，必须设置系统接地以提供最小阻抗通路。设备就不会受到不正常的电流干扰。
一般在变电站交流电都要安装接地设备。另一方面，在半周期电流系统中接地必需由每一相的交流电来提供。特殊的，象NEC250型就可以用别的方法接地。
3.5 电气设备的接地
敷线金属导管一定要置于地面.。如果金属性敷线埋于地下因为温度升高而可以不放在地下，是因为这时有电压在这之间。这样对人是很危险的。人随时可以接触到来自大地的过电流。
所有的非金属设备用电应紧紧的连接而且安装在一个放在地面上的电极上。好的连接电会是电流紧密的附着在金属上，并且当有事故发生时会迅速通过短路电流的电。如果励磁涌流足够大，可以使设备自动关闭。（1）错误的地面保护
GPF是一种当接地电流达到预设值时能够检测到接地故障并断开电路的设备。GFCI是一种当小电流通过时断开电路的设备。
没有办法预先知道来自地面外的阻抗。大多数的线路是在15安或者更大电流的保护之上。如果地面阻抗够低时甚至低于开启电流时, 如此通过的电流少于15安怎么办?这已经被证明像50毫安的小电流，虽然小，但是能使心，肺或脑死亡。
电气设备暴露在湿润的空气中可能产生震动或者高阻抗。严重时可能引起设备着火，然而电流可能是少于一个安培。设备中的污垢存在于变压器及线圈中. 操作不当有时会使电流通过身体而发生触电。
错误的地面保护有时候会少于15安。GFCI设计为按照双线电路工作，双线中的一根线接地。标准的线路电压在120伏到277伏之间。这个时候当你的线圈接地时你要花费很大的力气去操作。10毫安甚至更小的电流在这之前都有可能使线圈断开。20毫安的电流有时也会引起GFCI 装置在0.04秒内触动。
GFCI 装置的电流有时侯大量通过两个电路.当接地装置发生接地故障时,大部分是通过接地线圈来输送电能的,这就是接地故障的来源.它在两个电路中以不同的值来衡量.所有的错误的接地保护都可以在线圈里面以不变的电流来表示.
错误的地面保护通常是为了商业及工业的安装而设计. 他们的预设值可以从2安到2000安.GFCI装置通常嵌入在单相电路中.GFP通常用于
三线单相和三相电路中,而GFIC用于两线单相电路中.
一个错误的地面保护装置是在附着于线路中的,包括中间线圈,当有不正常电流通过时,所有的短路电流都通过线圈往外面送.这时在这些电路中电流值会下降到零.当单相接地保护发生故障时,过电流保护就会起作用.在这种情况下触动点会起动.当预值电流超过时,隔离装置会自动切断电流.
有时GFP 装置在系统中处于领导者. 在这种情况之下, 每一相都会设地面保护.当你起动GFP 装置时会引起线路的开断.
地面保护系统实际上是一种特殊的对于短路情况的设计.
（2）三相系统
在正常的用电系统中三相是这样描述的.在理想的情况下，这些系统是在正常情况下运行的，但是如果遇到故障,线路中电压为零.不过很少遇到这种情况.一般在工厂工人很难碰到这种情况然而,一旦发生了整个系统会在低于电压下不正常工作.单一的负荷时常是由三相系统供应的,单相电压如果经常发生变化,则三相系统也会发生变化.
4 电力变压器的选择
变压器的选择对变电站的造价有主要的影响，因为变压器为变电站造价中的不要项目。铭牌额定值仅是变压器应用的一个指导，只是选择过程的第一步。
选择变压器时应仔细评估一些其它的因素：
（1）阻抗的选择要考虑他们对短路负荷和低压侧断路器额定值的影响作用，变电站初期情况和将来的发展都要考虑到。此外，要实现变压器并联运行时的恰当负荷分配，阻抗值是重要的。
（2）无载分接范围选择应能提供正确的低压侧母线电压。
（3）若在负荷变化周期中，高压侧或低压侧的电压有较大范围的变化，就有必要提供母线电压的调节。实际调节量可利用系统特性和负荷特性来计算。
5 开关装置
开关装置是包括开关设备和切断设备的总名称，也包括附属的控制、测量、保护和调节设备。
开关装置主要包括断路器、隔离开关、负荷开关和熔断器。按功能来讲，隔离开关是最简单的开关，仅在很小电流下操作。隔离不能开断正常负荷电流，其功能只能是在变压器断路器或其他设备和高压短导线中的电流由断路器负荷开关断开后再进行断开和接通。负荷开关可开断正常负荷电流但不能开断短路电流。然而，断路器可执行上述两种开关的开断功能，但若在额定范围内使用，也可开断出现于系统中所有短路电流。熔断器基本由可熔断元件和熄弧装置组成。
断路器和隔离开关在短时额定范围内应不能被短路电流熔断或损坏。断路器和开关的设计或保护应能在断开状态下耐受正常的工作电压。
6 无功补偿的措施
线路电容对线路电压有两个影响。一个影响是由于线路电容电流流过线路电感引起的电压沿线路升高，第二个影响是线路电容电流流过电源阻抗引起的电压升高。这些影响可通过发电机电压调节器加以校正。若线路传送的充电电流太大，发电机的励磁磁场就非常弱，这将降低稳定性限度，因而是不能接受的。通过采用并联电抗器可降低前述的电压升高。电抗器所提供的补偿度通常可由被补偿线路电容的百分数来量化。超高压线路并联补偿的范围从0%到90%，变电站中电抗器接在线路的一端或两端。
并联电容器组的基本目的是要提高当地线路的电压，或提高此线路所带负荷的功率因数。许多大容量电容器组根据系统对无功容量需要的变化而投切。若轻负荷时电容器上电压太高，就切除一些或全部电容器。容量非常大的电容器组通常分批逐步地进行投切，这样做有需要更多开关的缺点，因此就增加了单位千伏总成本。然而，这确实提供了保持每步电压变化在允许范围内的方法。
同步调相机只不过是一种以同步转速运转的不带机械负荷的同步电机。调相机带有控制其励磁磁场以提供电压控制的控制电路。当系统电压降至要求值以下时，控制电路就自动增大励磁磁场，这使同步调相机向系
统提供无功功率，从而提高该处的系统电压。
静止无功补偿设备是利用电抗器和电容器结合大功率半导体装置而构成的一种可控无功电源。
7 过电压和绝缘配合
电力系统设计的一个极重要方面是考虑线路、电缆和变电站的绝缘要求。
当雷电击到输电线路的相导线上，雷击电流遇到导线的波阻抗，这样就产生过电压，并以波的形式沿线路传至变电站。此类过电压称为雷电侵入波。它将对变电站中的电气设备造成危害。
绝缘配合是确定各电气设备的正确雷电冲击绝缘水平和操作冲击绝缘水平以及确定正确避雷器的过程。此过程由已知的设备冲击特性和避雷器特性来确定。
8 接地
电力系统中的接地是为了运行上的考虑，防雷，以及保护人员和设备的安全。接地是指与具有低电阻的接地电极或良好的接地系统相连。接地装置应该有通过最大故障电流的载流容量，且具有足够低的接地电阻以避免此时人员可达到的任何点上出现危险电压。接地的布置应保证在故障情况下，实际出现于设备接地部位与大地之间的电压达到最低值，这样，已接地设备的绝缘就不会击穿或烧坏。在故障期间，电流流入地中时会在变电站内及周围地面上形成电位梯度。若不采取措施，地面电位差足够大到可能危及在该处行走的人员。此外，此种电位差有时可能出现在“接地”结构，或设备的构架与附近的地之间。由此考虑，变电站通常的做法是采用由水平埋设导体构成的电气接地系统。
Electric power system
1 Technical Characteristics of Electric Power
The electric power has unique technical characteristics which give the power industry certain unique characteristics.
1Intangibility. The customer cannot directly detect a kilowatt-hour with any of his physical senses.
2Quality. The quality of service can be measured by service continuity or reliability, uniformity of voltage at the proper level, proper and
uniform frequency of the alternating voltage.
3Product storage. Unlike most businesses, the electric power utility must create its product simultaneously with its use because there is no
storage of electricity.
4Responsibility for power service. Because the utility delivers its product to the customer’s premises it must assume responsibility for
the safe and reliable delivery of its product.
5Public Safety. The utility must provide reasonably adequate protection for the public and its own skilled workers.
2 Power System Planning
In anticipation of continued growth in the loads served by the electric utilities, power systems must be continually expanded in capability. Long-range planning is essential to assure that necessary additions are technically adequate, reasonable in cost and fit into a growth pattern.The difficulties encountered by the long-range planner include: uncertainty of load growth with respect to both geography and time, the probability of new invention or technological development.Good system planning strives for optimum design on a system-wide basis, not necessarily for minimum cost in one part of the system without regard to the effect on the other parts.In recent years, there has been an emphasis on economy in planning and operation.Now
there is increased emphasis on reliability and environmental factors.
Before planning decisions are made, many factors must be carefully considered:
(1)Equipment decision have long-term effects requiring a forecast and study period of 15-25 years.
(2)There are many alternate means of generating electric power nuclear, base-load fossil, mid-range combustion turbines or hydro, and in large-medium or small-size plants, and different forms of energy storage.
(3)There are several alternate means of transmitting electric power, for example, by alternating or direct current, overhead or underground cable, and all over a wide range of voltages.
(4)The planning decisions are affected by load management techniques and the load patterns.
(5)Uncertainty exists concerning the factors, such as future fuel cost, interest rates on money and capital availability, equipment forced-outage rates, new technologies and environmental restrictions.
3 Electrical Distribution
3.1 Primary Distribution Systems
The wiring between the generating station and the final distribution point is called the primary distribution systems. There are several methods used for transmitting the power between these two points. The two most common methods are the radial system and the loop system.
（1）The Radial Systems
The term radial comes from the word radiate, which means to send out or emit from one central point. A radiate system is an electrical transmission system which begins at a central station and supplies power to various substations.
In its simplest from, a radial system consists of a generating station which
produces the electrical energy. This energy is transmitted from the generator(s) to the central station, which is generally part of, or adjacent to, the generating station. At the central station the voltage is stepped up to a higher value for long-distance transmission.
From the central station, several lines carry the power to various substations. At the substations the voltage is usually lowered to a value more suitable for distribution in populated areas. From the substations, lines carry the power to distribution transformers. These transformers lower the voltages to the value required by the consumer.
（2）The loop system
The loop system starts from the central station or a substation and makes a complete loop through the area to be served, and back to the starting point. This results in the area being supplied from both ends, allowing sections to be isolated in case of a breakdown. An expanded version of the loop system consists of several central stations joined together to from a very large loop. （3）Consumer Distribution Systems
The type of distribution system that the consumer uses to transmit power within the premises depends upon the requirements of the particular installation. Residential occupancies generally use the simplest type. Commercial and industrial systems vary widely with load requirements.
3.2 Single-phase Systems
Most single-phase systems are supplied from a three-phase primary. The primary of a single-phase transformer is connected to one phase of the three-phase system. The secondary contains two coils connected in series with a midpoint tap to provide a single-phase, three-wire system. This arrangement is generally used to supply power to residential occupancies and some commercial establishments.
For residential occupancies, the service conductors are installed either
overhead or underground. Single-family and small multifamily dwellings have the kilowatt-hour metes installed on the outside of the building. From the kilowatt-hour meter, the conductors are connected to the main disconnect.
Three separate disconnecting means are used with one common ground.
From the main disconnect, the conductors supply power to the branch circuit panels. For dwelling occupancies there are three basic types of branch circuits: general lighting circuits, small appliance and laundry circuits, and individual branch circuits. The individual branch circuits are frequently used to supply central heating and/or air-conditioning system, water heaters, and other special loads.
（1）Grounding Requirements
All AC services are required to be grounded on the supply side of the service disconnecting means. This grounding conductor runs from the combination system and equipment ground to the grounding electrode. For multifamily occupancies it is permitted to use up to six service disconnecting means. A single grounding conductor of adequate size should be used for the system ground.
（2）Commercial and Industrial Installations
Commercial and industrial installations are more complex than small residential installations. Large apartment complexes and condominiums, although classified as residential occupancies, often use commercial-style services .A single-phase, three-wire service or a three-phase, four-wire service may be brought into the building, generally from underground. The service-entrance conductors terminate in a main disconnects. From this point, the conductors are connected to the individual kilowatt-hour meters for each apartment and then to smaller disconnecting means and over-current protective devices. Branch-circuit panels are generally installed in each apartment. Feeder conductors connect the individual disconnecting means to the
branch-circuit panels. Commercial and/or industrial buildings may have more than one kilowatt-hour meter, depending upon the number of occupancies. The service is usually a three-phase, four-wire system. The available voltages may be 120/208V or 277/480v. If the system provides 277/480V, a transformer must be installed in order to obtain 120V. If the building covers a large area, it is recommended that the service be installed near the center of the building. This arrangement minimizes line loss on feeder and branch-circuit conductors. Some utilities supply a three-phase, three-wire or three-phase, four-wire delta system. The common voltages that may be obtained from the three-wire delta system are 240V, 440V, or 550V. With this arrangement, a transformer must be used to obtain 120V. The usual voltages supplied from the four-wire delta system are 240V, three phase and 120V, single phase.
Many large consumers purchase the electrical energy at the primary voltage, and transformers are installed on their premises. Three-phase voltages up to 15 KV are often used.
The service for this type of installation generally consists of metal cubicles called a substation unit. The transformers are either installed within the cubicle or adjacent to it. Isolation switches of the drawer type are installed within the cubicle. These switches are used to isolate the main switch or circuit breaker from the supply during maintenance or repair.
3.3 Consumer Loop Systems
Although the radial system of distribution is probably the most commonly used system of transmitting power on the consumer’s property, the loop system is also employed.
When installing any system, over-current protection and grounding must be given primary consideration. Electrical personnel who design and install these systems must comply with the NEC and local requirements.
3.4 Secondary High-voltage Distribution
Large industrial establishments may find it more economical to distribute power at voltages higher than 600V. Depending upon the type of installation and the load requirements, voltages as high as 2300V may be used. Step-down transformers are installed in strategic locations to reduce the voltage to a practical working value.
Sometimes the high-voltage system may be radial, and the low-voltage system may be connected into a loop. Another method is to have both the primaries and secondary connected to from a loop.
（1）Secondary Ties Loop System
It is frequently convenient to connect loads to the secondary conductors at points between transformers. These conductors are called secondary ties. Article 450 of the NEC gives specific requirements regarding the conductor sizes and over-current protection.
（2）Grounding of Electrical Systems
In general, most electrical systems must be grounded. The purpose of grounding is to limit the magnitude of voltage caused by lightning, momentary surges, and accidental contact with higher voltages. System grounds must be arranged to provide a path of minimum impedance in order to ensure the operation of over-current devices when a ground fault occurs. Current should not flow though the grounding conductor during normal operation.
Direct-current systems generally have the grounding conductor connected to the system at the supply station, and not at the individual service. Alternation-current system, on the other hand, must be grounded on the supply side of the main disconnect at each individual service. For specific information on the location and method of grounding, refer to NEC Article 250.
3.5 Grounding of Electrical Equipment
Metal conduit and cases which enclose electrical conductors must be grounded. If the ungrounded conductor comes in contact with a metal
enclosure which is not grounded, a voltage will be present between the enclosure and the ground. This presents a potential hazard. Persons coming in contact with the enclosure and ground will complete a circuit.
All non-current-carrying metal parts of electrical installations should be tightly bonded together and connected to a grounding electrode. Good electrical continuity should be ensured though all metal enclosures. The current caused by accidental grounds will be conducted though the enclosures, the grounding electrode to the earth.
If the current is large enough, it will cause the over-current device to open.
（1）Ground-Fault Protection
A ground-fault protector is a device which senses ground faults and opens the circuit when the current to ground reaches a predetermined value. A ground-fault circuit interrupter is a device which opens the circuit when very small currents flow to ground.
There is no way to determine in advance the impedance of an accidental ground. Most circuits are protected by 15A or larger over-current devices. If the impedance of a ground fault is low enough, such devices will open the circuit. What about currents of less than 15A? It has been proven that currents as small as 50mA though the heart, lungs, or brain can be fatal.
Electrical equipment exposed to moisture or vibration may develop high-impedance grounds. Arcing between a conductor and the frame of equipment may cause a fire, yet the current may be less than 1 ampere. Leakage current caused by dirt and/or moisture may take place between the conductor and the frame. Portable tools are frequently not properly grounded, and the only path to ground is through the body of the operator.
The ground-fault circuit interrupter was developed to provide protection against ground-fault currents of less than 15A. The GFCI is designed to
operate on two-wire circuits in which one of the two wires is grounded. The standard circuit voltages are 120V and 277V .The time it takes to operate depends upon the value of the ground-fault current. Small currents of 10mA or less may flow for up to 5s before the circuit is opened. A current of 20mA will cause the GFCI to operate in less than 0.04s. This time/current element provides a sufficient margin of safety without nuisance tripping.
The GFCI operates on the principle that an equal amount of current is flowing through the two wires. When a ground fault occurs, some of the current flowing though the ungrounded wire; it completes the circuit though the accidental ground. The GFCI senses the difference in the value of current between the values of current between the two wires and opens the circuit. GFIC s may be incorporated into circuit breaks, installed in the line, or incorporated into a receptacle outlet or equipment.
Ground-fault protectors are generally designed for use with commercial and/or industrial installations. They provide protection against ground-fault currents from 2A up to 2000A.GFPs are generally installed on the main, submain, and/or feeder conductors. GFCIs are installed in the branch circuits.
A ground-fault protector installed on supply conductors must enclose all the circuit conductors, including the neutral, if present. When the operating is under normal conditions, all the current to and from the load flows though the circuit conductors. The algebraic sum of the flux produced by these currents is zero. When a phase-to-ground fault occurs, the fault current returns though the grounding conductor. Under this condition an alternating flux is produced within the sensing device. When the fault current reaches a predetermined value, the magnetic flux causes a relay to actuate a circuit breaker.
Sometimes the GFP is installed on the grounding conductor of the system. Under this condition, the unit senses the amount of phase-to-ground current flowing in the grounding conductor. When the current exceeds the
setting of the GFP, it will cause the circuit breaker to open.
The ground-fault protector is actually an especially design current transformer connected to a solid-state relay.
（2）Three-phase Systems
The various three-phase systems in normal use will be described. Under ideal conditions, these systems operate in perfect balance, and if a neutral conductor is present it carries zero current. In actual practice, perfectly balanced systems are seldom encountered. The electrical worker, therefore, must be able to calculate values of current and voltage in unbalanced systems. Single-phase loads are frequently supplied from three-phase systems. The single-phase load requirements vary considerably, making it virtually impossible to maintain a perfect balance.
To calculate the line currents in an unbalanced three-phase system, the method in the following example may be used.
4 Selection of Power Transformer
The selection of the transformer can have a major impact on the cost of a substation, since the transformer represents the major cost https://www.360docs.net/doc/f79789349.html,plate rating is only a aide to transformer application, and should only be used as a first step in the selection process.
The selection of the transformer should involve a careful evaluation of a number of other factors:
(1)Impedances should be selected considering their effects on
short-circuit duties and low-side breaker ratings both for initial and
future station developments.In addition, impedance is important to
achieve a proper load division in the parallel operation of
transformers.
(2)No load tap ranges should be selected to provide an adequate low-side
bus voltage.
(3)If the high-side or low-side voltages vary over a wide range during the load cycle, it may be necessary to provide bus regulation.The actual regulation can be calculated using the system and load characteristics.
5 Switchgear
Switchgear is a general term covering switching and interrupting devices, also associated devices with control, metering, protective and regulatory equipment.
Switchgear mainly includes circuit breaker, disconnecting switch, load-break switch and fuse.The disconnect switch is the simplest switch on the basis of function, operating only in the absence of appreciable current. This switch cannot open normal load current and its function is to disconnect or connect transformers, circuit breakers, other pieces of equipment and short length of high voltage conductors only after current through them has been interrupted by opening a circuit breaker or load-break switch. A load-break switch will switch normal load currents but will not interrupt short circuit currents. However, circuit breakers will perform the switching functions of the above two classes, but will, if applied within rating, interrupt all short circuit currents that may occur on the system. Fuses consist essentially of a fusible element and an arc-extinguishing means.
C ircuit breakers and disconnect switches should not be blown open or otherwise damaged by short circuit currents within their short time ratings. The circuit breakers and disconnecting switches should be designed or protected to withstand normal operating voltages across the device in the open position.
6 Means of Reactive Power Compensation
T he capacitance of a line has two related voltage effects.One is the rise in voltage along the line resulting from the capacitive current of the line flowing through the line inductance.The second effect is the rise in voltage
resulting from the capacitive current of the line flowing through the source impedance.These effects are corrected by the generator voltage regulators.If the line delivers too much charging current, the generator field excitation will become very low which reduces the stability limit and is unacceptable.These voltages can be reduced by the application of shunt reactors.The degree of compensation provided by a reactor is usually quantified by the percentage of the line capacitance that is compensated.The percent shunt compensation of EHV lines in service ranges from 0% to 90% with the reactors located in the substations at one or both ends of the line.
The basic purpose of a shunt capacitor bank is to increase the local circuit voltage or improve the load power factor carried by the circuit.Many large capacitor banks are switched on and off as the system need for reactive kilovolt amperes changes.System requirements govern whether a certain bank should or should not be switched.If the voltage at the capacitor would be too high during knight load, some or all of the capacitors are switched off.Very large banks are usually switched in steps.This procedure has the disadvantage of requiring more switches and thus increasing the total equipment cost per kilovar. It, however, provide a means of keeping the voltage change per step within permissible limits.
A synchronous condenser is nothing more than a synchronous machine running at synchronous speed witch no mechanical load.The condenser has a control circuit that controls the field excitation to provide voltage control. When the system voltage starts to fall below the desired values, the control circuit will automatically increase the field excitation which causes the synchronous condenser to supply vats to the system. This will increase the system voltage at the point.
7 Overvoltage and Insulation Coordination
A n area of critical importance in the design of power system is the
工业设计专业英语英文翻译
工业设计原著选读 优秀的产品设计 第一个拨号电话1897年由卡罗耳Gantz 第一个拨号电话在1897年被自动电器公司引入，成立于1891年布朗强，一名勘萨斯州承担者。在1889年，相信铃声“中央交换”将转移来电给竞争对手，强发明了被拨号系统控制的自动交换机系统。这个系统在1892年第一次在拉波特完成史端乔系统中被安装。1897年，强的模型电话，然而模型扶轮拨条的位置没有类似于轮齿约170度,以及边缘拨阀瓣。电话，当然是被亚历山大格雷厄姆贝尔（1847—1922）在1876年发明的。第一个商业交换始建于1878（12个使用者），在1879年，多交换机系统由工程师勒罗伊B 菲尔曼发明,使电话取得商业成功,用户在1890年达到250000。 直到1894年，贝尔原批专利过期，贝尔电话公司在市场上有一个虚拟的垄断。他们已经成功侵权投诉反对至少600竞争者。该公司曾在1896年，刚刚在中央交易所推出了电源的“普通电池”制度。在那之前，一个人有手摇电话以提供足够的电力呼叫。一个连接可能仍然只能在给予该人的名义下提出要求达到一个电话接线员。这是强改变的原因。 强很快成为贝尔的强大竞争者。他在1901年引进了一个桌面拨号模型，这个模型在设计方面比贝尔的模型更加清晰。在1902年，他引进了一个带有磁盘拨号的墙面电话，这次与实际指孔，仍然只有170度左右在磁盘周围。到1905年，一个“长距离”手指孔已经被增加了。最后一个强的知名模型是在1907年。强的专利大概过期于1914年，之后他或他的公司再也没有听到过。直到1919年贝尔引进了拨号系统。当他们这样做，在拨号盘的周围手指孔被充分扩展了。 强发明的拨号系统直到1922年进入像纽约一样的大城市才成为主流。但是一旦作为规规范被确立，直到70年代它仍然是主要的电话技术。后按键式拨号在1963年被推出之后，强发明的最初的手指拨号系统作为“旋转的拨号系统”而知名。这是强怎样“让你的手指拨号”的。 埃姆斯椅LCW和DCW 1947 这些带有复合曲线座位，靠背和橡胶防震装置的成型胶合板椅是由查尔斯埃姆斯设计，在赫曼米勒家具公司生产的。 这个原始的概念是被查尔斯埃姆斯（1907—1978）和埃罗沙里宁（1910—1961）在1940年合作构想出来的。在1937年，埃姆斯成为克兰布鲁克学院实验设计部门的领头人，和沙里宁一起工作调查材料和家具。在这些努力下，埃姆斯发明了分成薄片和成型胶合板夹板，被称作埃姆斯夹板，在1941年收到了来自美国海军5000人的订单。查尔斯和他的妻子雷在他们威尼斯，钙的工作室及工厂和埃文斯产品公司的生产厂家一起生产了这批订单。 在1941年现代艺术博物馆，艾略特诺伊斯组织了一场比赛用以发现对现代生活富有想象力的设计师。奖项颁发给了埃姆斯和沙里宁他们的椅子和存储碎片，由包括埃德加考夫曼，大都会艺术博物馆的阿尔弗雷德，艾略特诺伊斯，马尔塞布鲁尔，弗兰克帕里什和建筑师爱德华达雷尔斯通的陪审团裁决。 这些椅子在1946年的现代艺术展览博物馆被展出，查尔斯埃姆斯设计的新的家具。当时，椅子只有三条腿，稳定性问题气馁了大规模生产。 早期的LCW（低木椅）和DWC（就餐木椅）设计有四条木腿在1946年第一次被埃文斯产品公司（埃姆斯的战时雇主）生产出来，被赫曼米勒家具公司分配。这些工具1946年被乔治纳尔逊为赫曼米勒购买，在1949年接手制造权。后来金属脚的愿景在1951年制作，包括LCW（低金属椅）和DWC（就餐金属椅）模型。配套的餐饮和咖啡桌也产生。这条线一直
毕业论文英文参考文献与译文
Inventory management Inventory Control On 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 of
毕业设计外文翻译资料
外文出处： 《Exploiting Software How to Break Code》By Greg Hoglund, Gary McGraw Publisher : Addison Wesley Pub Date : February 17, 2004 ISBN : 0-201-78695-8 译文标题： JDBC接口技术 译文： JDBC是一种可用于执行SQL语句的JavaAPI（ApplicationProgrammingInterface应用程序设计接口）。它由一些Java语言编写的类和界面组成。JDBC为数据库应用开发人员、数据库前台工具开发人员提供了一种标准的应用程序设计接口，使开发人员可以用纯Java语言编写完整的数据库应用程序。 一、ODBC到JDBC的发展历程 说到JDBC，很容易让人联想到另一个十分熟悉的字眼“ODBC”。它们之间有没有联系呢？如果有，那么它们之间又是怎样的关系呢？ ODBC是OpenDatabaseConnectivity的英文简写。它是一种用来在相关或不相关的数据库管理系统（DBMS）中存取数据的，用C语言实现的，标准应用程序数据接口。通过ODBCAPI，应用程序可以存取保存在多种不同数据库管理系统（DBMS）中的数据，而不论每个DBMS使用了何种数据存储格式和编程接口。 1．ODBC的结构模型 ODBC的结构包括四个主要部分：应用程序接口、驱动器管理器、数据库驱动器和数据源。应用程序接口：屏蔽不同的ODBC数据库驱动器之间函数调用的差别，为用户提供统一的SQL编程接口。 驱动器管理器：为应用程序装载数据库驱动器。 数据库驱动器：实现ODBC的函数调用，提供对特定数据源的SQL请求。如果需要，数据库驱动器将修改应用程序的请求，使得请求符合相关的DBMS所支持的文法。 数据源：由用户想要存取的数据以及与它相关的操作系统、DBMS和用于访问DBMS的网络平台组成。 虽然ODBC驱动器管理器的主要目的是加载数据库驱动器，以便ODBC函数调用，但是数据库驱动器本身也执行ODBC函数调用，并与数据库相互配合。因此当应用系统发出调用与数据源进行连接时，数据库驱动器能管理通信协议。当建立起与数据源的连接时，数据库驱动器便能处理应用系统向DBMS发出的请求，对分析或发自数据源的设计进行必要的翻译，并将结果返回给应用系统。 2．JDBC的诞生 自从Java语言于1995年5月正式公布以来，Java风靡全球。出现大量的用java语言编写的程序，其中也包括数据库应用程序。由于没有一个Java语言的API，编程人员不得不在Java程序中加入C语言的ODBC函数调用。这就使很多Java的优秀特性无法充分发挥，比如平台无关性、面向对象特性等。随着越来越多的编程人员对Java语言的日益喜爱，越来越多的公司在Java程序开发上投入的精力日益增加，对java语言接口的访问数据库的API 的要求越来越强烈。也由于ODBC的有其不足之处，比如它并不容易使用，没有面向对象的特性等等，SUN公司决定开发一Java语言为接口的数据库应用程序开发接口。在JDK1．x 版本中，JDBC只是一个可选部件，到了JDK1．1公布时，SQL类包（也就是JDBCAPI）
毕业设计外文翻译附原文
外文翻译 专业机械设计制造及其自动化学生姓名刘链柱 班级机制111 学号1110101102 指导教师葛友华
外文资料名称： Design and performance evaluation of vacuum cleaners using cyclone technology 外文资料出处：Korean J. Chem. Eng., 23(6), (用外文写) 925-930 (2006) 附件： 1.外文资料翻译译文 2.外文原文
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工业设计外文翻译
Interaction design Moggridge Bill Interaction design，Page 1-15 USA Art Press, 2008 Interaction design (IxD) is the study of devices with which a user can interact, in particular computer users. The practice typically centers on "embedding information technology into the ambient social complexities of the physical world."[1] It can also apply to other types of non-electronic products and services, and even organizations. Interaction design defines the behavior (the "interaction") of an artifact or system in response to its users. Malcolm McCullough has written, "As a consequence of pervasive computing, interaction design is poised to become one of the main liberal arts of the twenty-first century." Certain basic principles of cognitive psychology provide grounding for interaction design. These include mental models, mapping, interface metaphors, and affordances. Many of these are laid out in Donald Norman's influential book The Psychology of Everyday Things. As technologies are often overly complex for their intended target audience, interaction design aims to minimize the learning curve and to increase accuracy and efficiency of a task without diminishing usefulness. The objective is to reduce frustration and increase user productivity and satisfaction. Interaction design attempts to improve the usability and experience of the product, by first researching and understanding certain users' needs and then designing to meet and exceed them. (Figuring out who needs to use it, and how those people would like to use it.) Only by involving users who will use a product or system on a regular basis will designers be able to properly tailor and maximize usability. Involving real users, designers gain the ability to better understand user goals and experiences. (see also: User-centered design) There are also positive side effects which include enhanced system capability awareness and user ownership. It is important that the user be aware of system capabilities from an early stage so that expectations regarding functionality are both realistic and properly understood. Also, users who have been active participants in a product's development are more likely to feel a sense of ownership, thus increasing overall satisfa. Instructional design is a goal-oriented, user-centric approach to creating training and education software or written materials. Interaction design and instructional design both rely on cognitive psychology theories to focus on how users will interact with software. They both take an in-depth approach to analyzing the user's needs and goals. A needs analysis is often performed in both disciplines. Both, approach the design from the user's perspective. Both, involve gathering feedback from users, and making revisions until the product or service has been found to be effective. (Summative / formative evaluations) In many ways, instructional
毕业论文外文翻译模板
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毕业设计英文翻译
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在目前的美国钢结构协会荷载抗力系数规范中，分析结构体系的方法是一阶弹性分析或二阶弹性分析。在使用一阶弹性分析时，考虑到二阶效果，一阶力矩都是由B1,B2系数放大。在规范中，所有细部都是从结构体系中独立出来，他们通过细部内力曲线和规范给出的那些隐含二阶效应，非弹性，残余应力和挠度的相互作用设计的。理论解答和实验性数据的拟合曲线得到了柱曲线和梁曲线，同时Kanchanalai发现的所谓“精确”塑性区解决方案的拟合曲线确定了梁柱相互作用方程。 为了证明单个细部内力对整个结构体系的影响，使用了有效长度系数，如图28.2所示。有效长度方法为框架结构提供了一个良好的设计。然而，有效长度方法的
土木工程毕业设计中英文翻译
附录：中英文翻译 英文部分： LOADS Loads that act on structures are usually classified as dead loads or live loads are fixed in location and constant in magnitude throughout the life of the the self-weight of a structure is the most important part of the structure and the unit weight of the density varies from about 90 to 120 pcf (14 to 19 KN/m)for lightweight concrete,and is about 145 pcf (23 KN/m)for normal calculating the dead load of structural concrete,usually a 5 pcf (1 KN/m)increment is included with the weight of the concrete to account for the presence of the reinforcement. Live loads are loads such as occupancy,snow,wind,or traffic loads,or seismic may be either fully or partially in place,or not present at may also change in location. Althought it is the responsibility of the engineer to calculate dead loads,live loads are usually specified by local,regional,or national codes and sources are the publications of the American National Standards Institute,the American Association of State Highway and Transportation Officials and,for wind loads,the recommendations of the ASCE Task Committee on Wind Forces. Specified live the loads usually include some allowance for overload,and may include measures such as posting of maximum loads will not be is oftern important to distinguish between the
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(文档含英文原文和中文翻译) 中英文翻译原文：
DESIGN and ENVIRONMENT Product design is the principal part and kernel of industrial design. Product design gives uses pleasure. A good design can bring hope and create new lifestyle to human. In spscificity,products are only outcomes of factory such as mechanical and electrical products,costume and so on.In generality,anything,whatever it is tangibile or intangible,that can be provided for a market,can be weighed with value by customers, and can satisfy a need or desire,can be entiled as products. Innovative design has come into human life. It makes product looking brand-new and brings new aesthetic feeling and attraction that are different from traditional products. Enterprose tend to renovate idea of product design because of change of consumer's lifestyle , emphasis on individuation and self-expression,market competition and requirement of individuation of product. Product design includes factors of society ,economy, techology and leterae humaniores. Tasks of product design includes styling, color, face processing and selection of material and optimization of human-machine interface. Design is a kind of thinking of lifestyle.Product and design conception can guide human lifestyle . In reverse , lifestyle also manipulates orientation and development of product from thinking layer.
毕业设计外文翻译
毕业设计（论文） 外文翻译 题目西安市水源工程中的 水电站设计 专业水利水电工程 班级 学生 指导教师 2016年
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毕业设计中英文翻译
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工业设计外文翻译---不需要设计师的设计
Design Without Designers 网站截图： https://www.360docs.net/doc/f79789349.html,/baidu?word=%B9%A4%D2%B5%C9%E8%BC%C6%D3%A2%CE%C4%CE%C4%CF%D 7&tn=sogouie_1_dg 原文： Design Without Designers I will always remember my first introduction to the power of good product design. I was newly arrived at Apple, still learning the ways of business, when I was visited by a member of Apple's Industrial Design team. He showed me a foam mockup of a proposed product. "Wow," I said, "I want one! What is it?" That experience brought home the power of design: I was excited and enthusiastic even before I knew what it was. This type of visceral "wow" response requires creative designers. It is subjective, personal. Uh oh, this is not what engineers like to hear. If you can't put a number to it, it's not important. As a result, there is a trend to eliminate designers. Who needs them when we can simply test our way to success? The excitement of powerful, captivating design is defined as irrelevant. Worse, the nature of design is in danger. Don't believe me? Consider Google. In a well-publicized move, a senior designer at Google recently quit, stating that Google had no interest in or understanding of design. Google, it seems, relies primarily upon test results, not human skill or judgment. Want to know whether a design is effective? Try it out. Google can quickly submit samples to millions of people in well-controlled trials, pitting one design against another, selecting the winner based upon number of clicks, or sales, or whatever objective measure they wish. Which color of blue is best? Test. Item placement? Test. Web page layout? Test. This procedure is hardly unique to Google. https://www.360docs.net/doc/f79789349.html, has long followed this practice. Years ago I was proudly informed that they no longer have debates about which design is best: they simply test them and use the data to decide. And this, of course, is the approach used by the human-centered iterative design approach: prototype, test, revise. Is this the future of design? Certainly there are many who believe so. This is a hot topic on the talk and seminar circuit. After all, the proponents ask reasonably, who could object to making decisions based upon data? Two Types of Innovation: Incremental Improvements and New Concepts In design—and almost all innovation, for that matter—there are at least two distinct forms. One is
本科毕业设计外文翻译(原文)
Real-time interactive optical micromanipulation of a mixture of high- and low-index particles Peter John Rodrigo, Vincent Ricardo Daria and Jesper Glückstad Optics and Plasma Research Department, Ris? National Laboratory, DK-4000 Roskilde, Denmark jesper.gluckstad@risoe.dk http://www.risoe.dk/ofd/competence/ppo.htm Abstract: We demonstrate real-time interactive optical micromanipulation of a colloidal mixture consisting of particles with both lower (n L < n0) and higher (n H > n0) refractive indices than that of the suspending medium (n0). Spherical high- and low-index particles are trapped in the transverse plane by an array of confining optical potentials created by trapping beams with top-hat and annular cross-sectional intensity profiles, respectively. The applied method offers extensive reconfigurability in the spatial distribution and individual geometry of the optical traps. We experimentally demonstrate this unique feature by simultaneously trapping and independently manipulating various sizes of spherical soda lime micro- shells (n L≈ 1.2) and polystyrene micro-beads (n H = 1.57) suspended in water (n0 = 1.33). ?2004 Optical Society of America OCIS codes: (140.7010) Trapping, (170.4520) Optical confinement and manipulation and (230.6120) Spatial Light Modulators. References and links 1. A. Ashkin, “Optical trapping and manipulation of neutral particles using lasers,” Proc. Natl. Acad. Sci. USA 94, 4853-4860 (1997). 2. K. Svoboda and S. M. Block, “Biological applications of optical forces,” Annu. Rev. Biophys. Biomol. Struct. 23, 247-285 (1994). 3. D. G. Grier, “A revolution in optical manipulation,” Nature 424, 810-816 (2003). 4. M. P. MacDonald, G. C. Spalding and K. Dholakia, “Microfluidic sorting in an optical lattice,” Nature 426, 421-424 (2003). 5. J. Glückstad, “Microfluidics: Sorting particles with light,” Nature Materials 3, 9-10 (2004). 6. A. Ashkin, “Acceleration and trapping of particles by radiation-pressure,”Phys. Rev. Lett. 24, 156-159 (1970). 7. A. Ashkin, J. M. Dziedzic, J. E. Bjorkholm and S. Chu, “Observation of a single-beam gradient force optical trap for dielectric particles,” Opt. Lett. 11, 288-290 (1986). 8. K. Sasaki, M. Koshioka, H. Misawa, N. Kitamura, and H. Masuhara, “Optical trapping of a metal particle and a water droplet by a scanning laser beam,” Appl. Phys. Lett. 60, 807-809 (1992). 9. K. T. Gahagan and G. A. Swartzlander, “Trapping of low-index microparticles in an optical vortex,” J. Opt. Soc. Am. B 15, 524-533 (1998). 10. K. T. Gahagan and G. A. Swartzlander, “Simultaneous trapping of low-index and high-index microparticles observed with an optical-vortex trap,” J. Opt. Soc. Am. B 16, 533 (1999). 11. M. P. MacDonald, L. Paterson, W. Sibbett, K. Dholakia, P. Bryant, “Trapping and manipulation of low-index particles in a two-dimensional interferometric optical trap,” Opt. Lett. 26, 863-865 (2001). 12. R. L. Eriksen, V. R. Daria and J. Glückstad, “Fully dynamic multiple-beam optical tweezers,” Opt. Express 10, 597-602 (2002), https://www.360docs.net/doc/f79789349.html,/abstract.cfm?URI=OPEX-10-14-597. 13. P. J. Rodrigo, R. L. Eriksen, V. R. Daria and J. Glückstad, “Interactive light-driven and parallel manipulation of inhomogeneous particles,” Opt. Express 10, 1550-1556 (2002), https://www.360docs.net/doc/f79789349.html,/abstract.cfm?URI=OPEX-10-26-1550. 14. V. Daria, P. J. Rodrigo and J. Glückstad, “Dynamic array of dark optical traps,” Appl. Phys. Lett. 84, 323-325 (2004). 15. J. Glückstad and P. C. Mogensen, “Optimal phase contrast in common-path interferometry,” Appl. Opt. 40, 268-282 (2001). 16. S. Maruo, K. Ikuta and H. Korogi, “Submicron manipulation tools driven by light in a liquid,” Appl. Phys. Lett. 82, 133-135 (2003). #3781 - $15.00 US Received 4 February 2004; revised 29 March 2004; accepted 29 March 2004 (C) 2004 OSA 5 April 2004 / Vol. 12, No. 7 / OPTICS EXPRESS 1417