变压器励磁涌流的抑制
变压器励磁涌流不仅导致继电保护误动，由其衍生的电网电压骤降、谐波污染、和应涌流、铁磁谐振过电压等都给电力系统运行带来不可低估的负面影响。数十年来人们通过识别励磁涌流特征的方法来减少继电保护的误动率，但并未获得良好的回报，误动率仍居高不下。至于对电压骤降、谐波污染、和应涌流等的消除更一筹莫展。究其原因是人们认为励磁涌流的出现不可抗拒，只能采用“识别”的对策，即“躲”的对策。其实，换个思路——“抑制”，是完全可以实现的，而且已经实现了。
引言
变压器励磁涌流与电容器的充电涌流抑制原理完全相似，电感及电容都是储能元件，前者不容许电流突变，后者不容许电压突变，空投电源时都将诱发一个暂态过程。在电力变压器空载接入电源时及变压器出线发生故障被继电保护装置切除时，因变压器某侧绕组感受到外施电压的骤增而产生有时数值极大的励磁涌流。励磁涌流不仅峰值大，且含有极多的谐波及直流分量。由此对电网及电器设备造成极为不利的影响。
1、励磁涌流的危害性
1.1 引发变压器的继电保护装置误动，使变压器的投运频频失败；
1.2 变压器出线短路故障切除时所产生的电压突增，诱发变压器保护误动，使变压器各侧负荷全部停电；
1.3 A电站一台变压器空载接入电源产生的励磁涌流，诱发邻近其他B电站、C 电站等正在运行的变压器产生“和应涌流”(sympathetic inrush)而误跳闸，造成大面积停电；
1.4 数值很大的励磁涌流会导致变压器及断路器因电动力过大受损；
1.5 诱发操作过电压，损坏电气设备；
1.6 励磁涌流中的直流分量导致电流互感器磁路被过度磁化而大幅降低测量精度和继电保护装置的正确动作率；
1.7 励磁涌流中的大量谐波对电网电能质量造成严重的污染。
1.8 造成电网电压骤升或骤降，影响其他电气设备正常工作。
数十年来人们对励磁涌流采取的对策是“躲”，但由于励磁涌流形态及特征的多样性，通过数学或物理方法对其特征识别的准确性难以提高，以致在这一领域里励磁涌流已成为历史性难题。
2、励磁涌流的成因
抑制器的重要特点是对励磁涌流采取的策略不是“躲避”，而是“抑制”。理论及实践证明励磁涌流是可以抑制乃至消灭的，因产生励磁涌流的根源是在变压
器任一侧绕组感受到外施电压骤增时，基于磁链守恒定理，该绕组在磁路中将产生单极性的偏磁，如偏磁极性恰好和变压器原来的剩磁极性相同时，就可能因偏磁与剩磁和稳态磁通叠加而导致磁路饱和，从而大幅度降低变压器绕组的励磁电抗，进而诱发数值可观的励磁涌流。由于偏磁的极性及数值是可以通过选择外施电压合闸相位角进行控制的，因此，如果能掌握变压器上次断电时磁路中的剩磁极性，就完全可以通过控制变压器空投时的电源电压相位角，实现让偏磁与剩磁极性相反，从而消除产生励磁涌流的土壤——磁路饱和，实现对励磁涌流的抑制。
长期以来，人们认为无法测量变压器的剩磁极性及数值，因而不得不放弃利用偏磁抵消剩磁的想法。从而在应对励磁涌流的策略上出现了两条并不畅通的道路，一条路是通过控制变压器空投电源时的电压合闸相位角，使其不产生偏磁，从而避免空投电源时磁路出现饱和。另一条路是利用物理的或数学的方法针对励磁涌流的特征进行识别，以期在变压器空投电源时闭锁继电保护装置，即前述“躲避”的策略。这两条路都有其致命的问题，捕捉不产生偏磁的电源电压合闸角只有两个，即正弦电压的两个峰值点（90°或270°），如果偏离了这两点，偏磁就会出现，这就要求控制合闸环节的所有机构（包括断路器）要有精确、稳定的动作时间，因为如动作时间漂移1毫秒，合闸相位角就将产生18°的误差。此外，由于三相电压的峰值并不是同时到来，而是相互相差120°，为了完全消除三相励磁涌流，必须断路器三相分时分相合闸才能实现，而当前的电力操作规程禁止这种会导致非全相运行的分时分相操作，何况有些断路器在结构上根本无法分相操作。
用物理和数学方法识别励磁涌流的难度相当大，因为励磁涌流的特征和很多因素有关，例如合闸相位角、变压器的电磁参数等。大量学者和工程技术人员通过几十年的不懈努力仍不能找到有效的方法，因其具有很高的难度，也就是说“躲避”的策略困难重重，这一策略的另一致命弱点是容忍励磁涌流出现，它对电网的污染及电器设备的破坏性依旧存在。
图2-1为一单相变压器结构图，可写出空载时初级绕组的电压方程
式中N1、R1分别为初级绕组的匝数及电阻。
式2.1可改写为（2.2）
式中α为 t=0时U1的初相角如忽略电阻R1，即
设R1=0，则得
求解（ 2.3）式微分方程得磁通Φ的表达式为
依据磁链守恒定理，合闸瞬间磁路中磁链不能突变，即可求出积分常数C。
式中
可写出磁通Φ表达式
式中为总磁通的幅值从式(2.6)中不难看出变压器外施电压u1在不同初相角α合闸时所产生的磁通Φ都不相同，将式(2.6)改写为
式(2.7)中为暂态磁通，即偏磁，在合闸瞬间Φp的值与α有关，在90°或270°空投时Φp=0，在0°或180°空投时Φp可达峰值Φm。式(2.7)中
为稳态磁通，为一周期函数。
图2-2为空投合闸角α=0时的磁通变化曲线，图中Φs为稳态磁通，Φ为Φs 和Φp合成的总磁通（未计及剩磁Φres），Φsat为变压器饱和磁通。对于无损变压器（R1=0）偏磁Φp不会衰减，如实线所示，对于有损变压器（R1>0）
Φp按时间常数衰减，如虚线所示。从图2-2中可看出在电压相位角在θ1至θ2区间总磁通Φ大于饱和磁通Φsat，磁路饱和，因而产生励磁涌
流iy，iy具有间断性。对于无损变压器Φ和iy是关于的偶对称波形，而在iy=0的间断角区间Φ则是关于的偶对称波形。对于有损变压器则Φ与iy将不再有对称关系。当计及剩磁时，总磁通将由剩磁、偏磁（暂态磁通）及稳态磁通三者组成。不难看出在图2-2偏磁的情况下，如剩磁为正，则总磁通曲线向上平移，即磁路更易饱和，励磁涌流
幅值会更大。如剩磁为负，则励磁涌流将被抑制。
图2-3是铁磁材料的磁滞回线，它描述在磁路的励磁线圈上施加交流电压时，磁势H也相应的从-Hc到Hc之间变化，由H产生的磁通Φ（或磁通密度B=Φ/S）将在磁滞回线上作相应的变化。如果H在回线上的某点突然减到零，则B将随即落到对应B轴的某点上，该点所对应的B值即为剩磁Br。可以看出剩磁的数值和极性与切除励磁电压的相位角有关，如果在第Ⅰ、Ⅱ象限切断励磁电源（即H=0）则剩磁为正或零，在Ⅲ、Ⅳ象限切断励磁电源，则剩磁为负。
3、励磁涌流的抑制方法
变压器在正常带电工作时，磁路中的主磁通波形与外施电源电压的波形基本相同，即是正弦波。磁路中的磁通滞后电源电压90°，通过监测电源电压波形实现对磁通波形的监测，进而获取在电源电压断电时剩磁的极性。变压器空投上电时产生的偏磁Φp也一样，因偏磁，电源电压上电时的初相角α在Ⅰ、Ⅳ象限区间内产生的偏磁极性为正，而初相角α在Ⅱ、Ⅲ象限区间内产生的偏磁极性为负。显然，剩磁极性可知，偏磁极性可控，只要空投电源时使偏磁与剩磁极性相反，涌流即被抑制。
变压器初级电压u、主磁通Φ、剩磁ΦRes及偏磁Φp与分闸角和合闸角的关系曲线图,以及电源电压u分闸初相角α’与剩磁ΦRes的关系曲线。变压器处于稳态时主磁通Φ滞后电源电压u 90°.变压器空载上电时所产生的偏磁一定与稳态时对应上电时电压u曲线上电点的稳态磁通大小相等，极性相反，其最大值可达稳态磁通Φ的峰值Φm，而剩磁ΦRes幅值与磁路材料的特性有关。不难看出对应同一个合闸初相角α或分闸初相角α’所产生的偏磁和剩磁的极性正好相反，也就是说通过分闸时测量电源电压分闸角α’，并将α’保存下来，在下次空投变压器时选择在合闸角α等于α’时加上电源，偏磁就可与剩
磁反向，它们的合成磁通将小于饱和磁通Φsat(曲线④)，（因饱和磁通一般选择大于稳态磁通峰值），磁路不会饱和，从而实现对励磁涌流的抑制。由于三相电源电压在断路器三相联动切除时所得到的三相分闸相角各相差120°，剩磁极性也是三相各相差120°，而在三相联动合闸时三相的合闸初相角也是相差120°，三相偏磁极性也各相差120°，这样就自然实现了变压器三相磁路中的偏磁和剩磁都是抵消的，从而避免了一定要断路器分相分时操作才能抑制励磁涌流的苛求，也就是说三相联动断路器支持对三相涌流的抑制。
由于抑制励磁涌流只要偏磁和剩磁极性相反即可，并不要求完全抵消，因而当合闸角相对前次分闸角有较大偏差时，只要偏磁不与剩磁相加，磁路就不会饱和，这就大大降低了对断路器操作机构动作时间的精度要求，为这一技术的实用化奠定了基础。将这种抑制器与快切装置和备自投装置联动即可实现备用变压器按冷备用方式运行，这将大大节约变压器热备用方式的空载能耗。
图3-1选录了四条励磁涌流Iy与分闸角α’和合闸角α的关系曲线，可以看到，在合闸角α为90°或270°时，空投变压器的励磁涌流与变压器的前次分闸角无关，原因是在变压器初级电压过峰值时上电不产生偏磁，不论变压器原来是否有剩磁都不会使磁路饱和。当然，如果使用三相联动断路器是不可能做到三相的偏磁都为零。而当合闸角α为0°或 180°时则空投变压器的励磁涌流与前次分闸角α’密切相关，当α与α’相近（大约相差±60°）时励磁涌流被抑制，此后α与α’偏离越大，励磁涌流也越大。由此可以看到如断路器的合闸时间漂移在±3ms时对涌流的抑制基本无影响。当今的真空断路器和SF6断路器的分、合闸时间漂移都在1ms之内，完全可以精确实现对励磁涌流的抑制。
图3-1 分闸角α’与合闸角α对励磁涌流的影响曲线
应该指出，变压器断电后留在三相磁路中的剩磁在正常情况下是不会衰减消失的，不会改变极性。只有在变压器铁心受到高于材料居里点的高温作用后剩磁
才会衰减或消失，但一般的电站现场不会出现这种情况。退一步讲，剩磁消失是件好事，只要没有剩磁，仅靠偏磁是不会引起磁路饱和的。
4、结束语
电力变压器空投充电相位角与前次切除电源相位角匹配原则，从理论及实践上都证明了在使用三相联动操作断路器时能彻底抑制励磁涌流。同样，电力电容器空投充电相位角与前次切除电源相位角匹配原则，也能实现抑制三相联动断路器合闸时的电容器充电涌流。这一技术对根除保护误动、改善电能质量、提高运行可靠性有重要意义。同样对各种电压等级电力系统的无功补偿、远距离输电线路的串联补偿控制等也有重要意义。
大学英语1考试卷 总分：100分 简答题 1、将下列句子翻译成汉语 1.We can do a lot of things onlinesuch assearching for information and communicating with friendsno matter how far.答案：我们可以在网上做很多事情，例如寻找信息及和朋友沟通，不管相距多远。 2.Some people seem tohave their own ability in learning language答案：有些人在学习语言方面似乎有自己的天赋. 3.It is necessary for them to learn the language in order to communicate with these people and to learn from them.答案：为了与这些人进行交流，向他们学习，学习这门语言是必要的 4.Our likes and dislikes, tastes and preferences that hide in our choices of such activities such as reading books, going to the cinema, camping, or certain cultural pursuits, are all related to social background and learning experiences.答案：我们的好恶、品位、喜好决定了我们是选择看书、看电影、露营或某种文化追求，这又同社会环境和学习经验有关。 5.Occasionally, for a formal party or dinner, an invitation requires an answer,either in writing or by telephone. 答案：偶尔,一个正式的聚会或晚宴, 被邀请人是需要做出明确答复的, 无论是通过书面或者电话. 选择性答案2：应邀出席正式宴会或晚餐，不管是用书面还是用电话，有时是要回复的。（意思差不多，哪个通顺写哪个吧） 6.They not only like playing or watching games, but also like talking about them, or even thinking about them. 答案：他们不仅喜欢玩游戏、看游戏，而且喜欢谈论和思考它们。 7.There are plenty out there that are good and plenty that are bad. 答案：那里有很多是好的，很多是坏的。 8.Yet putting off something we know we should do is a bad habit to get into. 答案：然而，拖延我们知道应该做的事就会染上一个坏习惯。 9.And don’t you feel stressed and worried when you have to hurry?
2017电大开放英语1形成性考核册答案（最新 无错版） 开放英语（1）形成性考核册作业1答案 选择题请在在选项上画√
1、请写出下列名词的复数形式。 Parent photo bus life half child w oman tooth Parents photos buses lives haves children women teeth 2、频度副词often,always,sometimes等在句中的位置是有规律的，请写出这些规律，并各举一个例句。 （1）在动词 to be之后： Are you always at home on Sunday? （2）在实意动词之前： I sometimes go to London. （3）在含有助动词的句子中，置于助动词之后，实意动词之前。 I do not often go to work by bus. 3、请写现在进行时的两种用法，并分别举一个例句。 （1）现在进行时表示此刻正在发生的事情或正在进行的动作。 He is talking to a customer.
（2）现在进行时也可以表示这一段时期正在进行的活动，虽然在此时此刻江没有进行。 LiJun is working on a new database at the moment ,but right now she is sleeping. 4、请用学过的功能句型介绍你自己的姓名、年龄、所在城市、工作。请用英语写（略） 开放英语（1）作业1 第一部分交际用语 1. A 2. B 3. B 4. B 5. A 第二部分词汇与结构 6. B 7. A 8. C 9 .C 10. C 11 .B 12 .B 13. C 14 .C 15. C 16. B 17. A 18. B 19. B 20. A 21. B 22. A 23. C 24. C 25. A 第三部分句型变换 26. He is a manager. Is he a manager? 27. She usually goes to work by bus. Does she usually go to work by bus? 28. There are fifty students in the class. Are there fifty students in the class? 29. They have a large house.
专业英语大作业 一：英译汉 翻译范围TCP/IP Illustrated, V olume 1: The Protocols 5.1~5.5 15.1~15.2 第5章RARP：逆地址解析协议 5.1简介 5.2 RARP报文格式 5.3 RARP示例 5.4 RARP服务的设计 5.5小结 练习 5.1简介 一个拥有本地磁盘的系统通常是从磁盘文件读取配置文件中获取其IP地址。但一个没有磁盘的系统，如X终端或无盘工作站，需要一些其它方式去获得其IP地址。 每个系统在网络上都有一个唯一的硬件地址，由网络接口的制造商分配。 RARP的原则是无盘系统从接口卡上读取其独特的硬件地址，并发送RARP请求（网络上的广播帧）要求别人对无盘系统的IP地址（使用RARP回应）进行应答。 虽然这个概念很简单，执行往往比ARP更难，在本章后面会描述其原因。 RARP的正式规范是RFC 903。 5.2 RARP报文格式 RARP报文的格式几乎与ARP报文是相同的（图4.3）。唯一的区别是，RARP 的请求或应答帧类型为0×8035，并且在操作层RARP请求值为3、RARP应答值为4。 图4-3 ARP在网络上请求与应答报文的格式 与ARP一样，RARP服务器请求是广播和RARP应答通常是单播。 5.3 RARP示例 在我们的网络，我们可以强制sun主机从网络引导，而不是它的本地磁盘。 如果我们在主机bsdi上运行RARP服务器和tcpdump，我们得到如图5.1所示的输出。我们使用-e参数去标记tcpdump的打印硬件地址：
图5.1 RARP请求和应答。 该RARP请求是广播（1号线）的，第2行的RARP应答是单播的。第2行的输出，“at sun”,意味着RARP应答包含了主机sun（140.252.13.33）的IP地址。 在第3行，我们看到，一旦sun接收其IP地址，它会发出一个TFTP读请求（RRQ）的文件8CFCOD21.SUN4C。（TFTP是简单文件传输协议，我们在第15章进行详细描述）。在文件名中的8个十六进制数字是sun主机的IP地址140.252.13.33的十六进制表示形式。这是在RARP应答中返回的IP地址。该文件名的其余部分，后缀SUN4C表示系统正在引导的类型。 Tcpdump表示第3行是一个长度为65的IP数据报，而不是一个UDP数据报（实际上它确实是），因为我们运行tcpdump命令使用-e参数，看硬件级别的地址。另一点，在图5.1要注意的是在第2行的以太网帧的长度似乎比最小较短（我们所说的是在4.5节60字节）。原因是我们的系统，该系统上运行的tcpdump 发送该以太网帧（BSDI）。该应用程序rarpd，写42字节到BSD分组过滤器装置（14字节的以太网报头和28字节的RARP应答），这是什么的tcpdump收到的副本。但以太网设备驱动程序垫这个短帧的最小尺寸为传输（60 ）。如果我们在另一个系统上已经运行的tcpdump ，长度会是60。 我们可以看到在这个例子，当这种无盘系统接收在RARP应答它的IP地址，它会发出一个TFTP请求来读取一个引导映像。在这一点上，我们不会进入其他详细介绍无盘系统是如何引导自己。（第16章介绍了使用RARP ，BOOTP和TFTP无盘X终端的引导顺序。） 图5.2表示出了如果有在网络上没有RARP服务器所得到的数据包。每个数据包的目的地址为以太网的广播地址。以太网地址跟随的是目标硬件地址，并按照发送端的硬件地址发送。
10108 大学英语（B） 一、单选题 What is NOT mentioned in US education system?（B） 选择一项： A. major courses B. teaching methods C. self-discipline of the students D. comparison with Chinese students 2.Which of the following statements is TRUE?（C） 选择一项： A. There are fewer and fewer universities and private colleges in America. B. The academic advisor is in charge of the student's living conditions. C. Required core classes are taken in the first school year. D. The student must stick to his majors throughout his college time. 3.About the courses in US colleges, which of the following is NOT TRUE?（C） 选择一项： A. Subjects of arts, sciences and languages are taken by most first year students. B. There are a number of other courses for students to choose from besides their major ones. C. Students would still get certain credits if they do not attend the courses. D. A typical course load means the credits of courses a student has for one semester. 4.If students have problems in finding jobs, they can turn to _____ for help.（B） 选择一项： A. academic advisors B. the Career Counseling and Placement Office C. some fraternities D. no organization 5.The successful college students probably are the following EXCEPT______.（A） 选择一项： A. self-centered B. active members of society during school C. members of some fraternities D. those who know how to control themselves 6.The fact that wife beating was legal in America in 1850 shows that ____C______. 选择一项： A. America's legal system was in favor of the husband B. American husbands didn't love their wives C. American wives were servants to their husbands
开放英语I（1）作业1 （Unit 1~6） 第一部分交际用语（10分） 1－5题: 阅读下面的小对话，判断稚是否恰当，恰当的选A（Right），不恰当的选B（Wrong）,并将答案写在各题前的（）中。（每题2分，共10分） (A) 1.－How old is the manager? -- He is 35 year old. A. Right B. Wrong (A) 2. – What do they do ? -- They work in a bank. A Right B. Wrong (B) 3. –Would you like some crisps? - No, I’m sorry.. A. Right B. Wrong (B) 4. – How much does the flat cost a month? - It’s on the tenth floor. A. Right B. Wrong (A) 5. – Could you sign the register, please? - Of course. A. Right B. Wrong 第二部分词汇与结构（40分） 6~25小题：阅读下面的句子，选择正确答案，并将所选项的字母符号写在各题前的（）中。（每题2分，共40分） （B）6. He _____ for an IT company. A. work B. works C. working (A) 7. I have coffee _____ breakfast time A. at B. in C. on (C) 8. _____ name is Wanghua. A. He B. He’s C. His (C) 9. She is _______ only accountant in my son’s company. A. a B. an C. the (C) 10. Maria often has a walk with _______ parents in the morning. A. she B. their C. her (B) 11. _________ you got any family ? A. Do B. Have C Has (B) 12. He’s responsible _____ the central computer system. A. in B. for C. of (C) 13. The Business Banking Department is on ____ floor. A. second B. the two C. the second (C) 14. Wang Li is _______ a new market campaign at the moment. A. plan B. planing C. planning (C) 15. Polly enjoys ________ the guitar in a band in her free time.
《自动化专业英语》翻译大作业 所选文字出处：选自论文《PLC的发展和应用》 班级：学号：姓名：成绩： PLC全名为可编程控制器，定义是种数字运算操作的电子系统，专为在工业环境应用而设计的，主要结构由电源，中央处理单元，存储器，输入输出接口电路，功能模块，通信模块组成。PLC具有通用性强、使用方便、适应面广、抗干扰性强、编程简单等特点，在军事、国防、航空航天、交通、工业生产中的地位，在可预见的将来中是无法取代的。PLC有很多流派，我国的PLC研发、生产和应用发展很快，尤其在应用方面更为突出。 PLC的发展历程和主要流派 在工业生产过程中，大量的开关量顺序控制，它按照逻辑条件进行顺序动作，并按照逻辑关系进行连锁保护动作的控制，及大量离散量的数据采集。传统上，这些功能是通过气动或电气控制系统来实现的。1968年美国GM（通用汽车）公司提出取代继电气控制装置的要求，第二年，美国数字公司研制出了基于集成电路和电子技术的控制装置，首次采用程序化的手段应用于电气控制，这就是第一代可编程序控制器，称Programmable Controller（PC）。个人计算机（简称PC）发展起来后，为了方便，也为了反映可编程控制器的功能特点，可编程序控制器定名为Programmable Logic Controller（PLC），现在，仍常常将PLC简称PC。PLC的定义有许多种。国际电工委员会（IEC）对PLC的定义是：可编程控制器是一种数字运算操作的电子系统，专为在工业环境下应用而设计。它采用可编程序的存贮器，用来在其内部存贮执行逻辑运算、顺序控制、定时、计数和算术运算等操作的指令，并通过数字的、模拟的输入和输出，控制各种类型的机械或生产过程。可编程序控制器及其有关设备，都应按易于与工业控制系统形成一个整体，易于扩充其功能的原则设计。上世纪80年代至90年代中期，是PLC发展最快的时期，年增长率一直保持为30~40%。在这时期，PLC在处理模拟量能力、数字运算能力、人机接口能力和网络能力得到大幅度提高，PLC逐渐进入过程控制领域，在某些应用上取代了在过程控制领域处于统治地位的DCS系统。在世界上200多家PLC厂商，400多品种的PLC产品大体可以按地域分成三个流派：一个流派是美国产品，一个流派是欧洲产品，还有一个流派是日本产品。同一地区的产品相互借鉴的比较多，相互影响比较大，技术参透比较深，面临的主要市场相同，拥护要求接近，这一切就使得同一地域的PLC产品表现出比较多的相似性。美国PLC技术的形成与欧洲PLC技术的形成是在相互隔离的情况下，独自研究开发获得的，因此美国的PLC产品与欧洲的PLC产品常表现出来明显的差异性。日本的PLC技术是由美国引进的，因此日本的产品对美国的产品有一定的继承性。世界上比较先进的PLC生产厂家有德国的的西门子、日本的三菱、美国的A-B公司等等。
电大开放英语《一》（1）形成性考核 册开放英语（1）作业1 第一部分交际用语（10分） 1一5小题：阅读下面的小对话，选择正确答案，并将所选项的字母符号写在各题前的（）中，红色为参考答案。（每题2分，共10分） （A）1．— How old is the manager? — He is 35 years old. A. Right. B. Wrong. （A）2．— What do they do? — They work in a bank. A. Right. B. Wrong. （B）3．— Would you like some crisps？ —No, I’m sorry. A. Right. B. Wrong. （B）4．— How much does the flat cost a month？ —It’s on the tenth floor. A. Right. B. Wrong. （A）5．— Could you sign the register, please?.
— Of course. A. Right. B. Wrong. 第二部分词汇与结构（40分） 6-25小题：阅读下面的句子，选择正确答案，并将所选项的字母符号写在各题前的（）中。（每题2分，共40分） （ B ）6. He __________ for an IT company. A. work B. works C. working （ A ）7. I have coffee _______ breakfast time. A. at B. in C. on （ C ）8. ______ name is Wanghua. A. He B. He’s C. His （ C ）9. She is _______ only accountant in my son's company. A. a B. an C. the （ C ）10. Maria often has a walk with ________parents in the morning. A. she B. their C. her （ B ）11. ___________ you got any family?
1、(5) Which of the following is not true? ADick stayed at a nice hotel in the center of the city. BDick didn't work on the first night of his arrival. CDick forgot to send his wife a telegram. DDick wanted to go back to his hotel in a taxi. 正确答案C 2、题目Reading comprehension 1(4) Who would send him the name and address of his hotel? AThe manager of his hotel. BThe police office. CThe taxi driver. DHis wife.
正确答案D 3、题目Reading comprehension 1(3)Where did Dick stay in New York? A In the center of the city. BIn a hotel. CIn a restaurant. DAt his friend's house. 正确答案B 4、题目Reading comprehension 1(2) Why did his wife want a telegram from him? ABecause she didn’t know his address yet
BBecause she wanted to go to New York, too CBecause she might send him another telegram DBecause she couldn't leave her husband by himself in New York. 正确答案A 5、1) Dick flew to New York because _________. Ahe went there for a holiday Bhe had work there Che went there for sightseeing D his home was there 正确答案B
大学英语三离线作业答 案 Document serial number【NL89WT-NY98YT-NC8CB-NNUUT-NUT108】
离线作业试卷列表2 一、单选? 1.第一部分：交际用语（共5小题；每小题3分，满分15分）- Would you be interested in seeing a film tonight- ____C______?分值：3 A. Not at all.??? B. Are you sure??? C. Great! I'd love to ??? D. You're welcome.???? 2.第一部分：交际用语（共5小题；每小题3分，满分15分）- Excuse me, could you tell me the way to P eople's Square- ____B______?分值：3 A. I don't understand you.??? B. Sorry, I'm a stranger here.??? C. Why don't you take a taxi??? D. Don't bother me.???? 3.第四部分：完形填空（共10小题；每小题1分，满分10分）30?C 分值：1 A. on mind??? B. in heart??? C. in mind??? D. on your mind???? 4.第四部分：完形填空（共10小题；每小题1分，满分10分）29 B?分值：1 A. with??? B. for??? C. to??? D. in???? 5.第四部分：完形填空（共10小题；每小题1分，满分10分）28 B?分值：1 A. impossible??? B. wonderful??? C. incapable??? D. practical???? 6.第一部分：交际用语（共5小题；每小题3分，满分15分）- I've got the first prize in the dancing ____C______?分值：3 A. You're welcome.??? B. It's very kind of you.??? C. Please accept my congratulations.??? D. Oh, really, I can't believe my ears.???? 7.第一部分：交际用语（共5小题；每小题3分，满分15分）- I've passed the ___D_______?分值：3 A. What a pity!??? B. I have the examination.??? C. Come on.??? D. Congratulations.???? 8.第一部分：交际用语（共5小题；每小题3分，满分15分）- I'm suffering from a ________A__?分值：3
Abstract: In the modern society, database technology is developing rapidly, and the data information contained therein is also increasing. In the process of enterprise operation, the database system is gradually being widely applied to daily information management, which is to effectively organize and utilize the massive information in the database through relevant technical means to help relevant data owners find valuable information and knowledge. Guide the development planning of the enterprise and improve the operational efficiency of the enterprise. This has become one of the hot topics of current e-commerce industry operators, and data mining technology can help e-commerce operators solve such problems. Data mining is a comprehensive use of related technologies such as artificial intelligence and natural language understanding. The purpose is to extract useful and valuable information or patterns from large amounts of data. This topic first analyzes and summarizes the research results of scholars at home and abroad, and makes a preliminary understanding of the application of data mining in e-commerce. Then it expounds the methods of data mining and e-commerce concepts and data mining. This paper also uses theoretical analysis and Case studies and other research methods, as well as questionnaire surveys of employees from different enterprises, fully discuss the difficulties in data mining technology in the field of e-commerce, the difficulties in the process of promotion, and the related methods to solve the bottleneck of e-commerce development. Research, in this way to explore the convergence of e-commerce development and data mining, and comprehensively promote the application of technological innovation. Through the research of this paper, we have an understanding of the application status of data mining technology in e-commerce. The problems and solutions can also provide a good platform for better application of data mining in e-commerce. Keywords: e-commerce; data mining; technical research; 1 Application status and development of data mining technology in e-commerce Data Mining Technology Application Overview: From a macro perspective, data mining technology is conducive to identifying and analyzing user behavior. In a larger depth and breadth, it summarizes users' consumption habits and behavioral preferences, which is beneficial to the subject and object to improve their service methods and product performance. To get a better customer experience and customer satisfaction. Data mining, as a high-level modern technology, has extremely complex logic and computational methods. The internal logic and methods also have different characteristics. According to a survey of 50 employees from different companies, data mining technology is widely used in e-commerce. In 74% of e-commerce, up to 81% of enterprises surveyed use data mining technology. The application of data mining technology in e-commerce is much higher than the percentage I expected. It can be seen that the current application is very wide.
开放英语（1）形考作业答案 作业1 第一部分交际用语 1. A 2. B 3. B 4. B 5. A 第二部分词汇与结构 6. B 7. A 8. C 9 .C 10. C 11 .B 12 .B 13. C 14 .C 15. C 16. B 17. A 18. B 1 9. B 20. A 21. B 22. A 23. C 24. C 25. A 第三部分句型变换 26. He is a manager. Is he a manager? 27. She usually goes to work by bus. Does she usually go to work by bus? 28. There are fifty students in the class. Are there fifty students in the class? 29. They have a large house. Have they a large house? / Do they have a large house? 30. He’s curren tly working on TV advertisements. Is he currently working on TV advertisements? 第四部分阅读理解 31．B 32．A 33．A 34．B 35．B 36.B 37.B 38.B 39.A 40.C 第五部分翻译41--45题：将下列英文句子翻译成中文。 41. The Meeting Rooms are on the ground floor. 会议室在一楼。 42. He ’s talking to a customer right now. 他此刻正在和一顾客讲话。 43. David usually have a sandwich in his office at lunchtime. 大卫午餐时间经常在办公室吃三明治。 44. I have a reservation for a single room. 我预定了一间单人间。 45. I’m waiting for an important telephone call from my boss in Shanghai.我在等我的上海老板的一个重要电话。 作业2 第一部分交际英语 1.A 2.B 3.B 4.A 5.A 第二部分词汇与结构 6.B 7.C 8.B 9.A 10.C 11.C 12.A 13.A 14.A 15.A 16.B 17.A 18.B 19.A 20.A 21.A 22.C 23.A 24.B 25.C 第三部分句型变换 26—30小题；将下列句子改写为否定句。 26. You can smoke in the bedrooms. You can not ( can’t ) smoke in the bedrooms. 27. It usually snows in winter in Ireland.
Exercises 1.When and where shall we ___A____. A.meet B. met C. to meet D. meeting A.You __D_____show more respect for your elders. A.can B. could C. would D. must 3. It is necessary that I ___D____ return the books to him tomorrow. A. will B. can C. may D. should 4. She __B_____ to school by school bus at eight in the morning. A. go B. goes C. went D. gone 5. What __C_____the notice say? A. is, say B. is, said C. did, say D. does, say 6. I’ll tell her after Ruby __B____. A. leave B. leaves C. left D. is leaving 7. We __D_____ the result tomorrow. A. know B. knew C. has known D. will know 8. On November 1 we __D_____ in this house for thirty years. A. live B. will have C. are living D. will have been living 9. It __B_____ to rain soon. A. is B. is going C. will D. shall 10. Mary ___C_____ a dress when she cut her finger.
Unit 1 1.—You speak very good English. — ___________________. A. No, my English is poor B. Don’t say that C. Thank you D. It’s a pleasure 2.— __________ have dinner with me this evening? —Yes. It’s very kind of you. A. Would you like to B. Don’t you like to C. Why don’t you D. Shouldn’t you 3. - I’m afraid Susan’s question made you angry. - ______. If I had been angry, I would have refused to answer. A. Do be afraid B. You are right C. Don’t worry D. Yes, it did 4.－I’m afraid I’ve got a terrible flu. －______________________. A. Never mind B. Keep away from me C. Better go and see a doctor. D. You need to be more careful 5.－It’s cold in here. Do you mind if I close the door?－______________________. A. With pleasure B. Yes, please C. Of course not D. Thank you 6.－I’m going to America for a holiday next week.－______________________. A. Goodbye B. Wish you success C. For sure D. That’s great 7.－Would you like a cup of coffee? －______________________. A. It’s very kind of you. B. No, I wouldn’t C. Yes, please D. Here you are 8. －Haven't seen you for ages. _______ －I've been in California for the past month. A. What are you up to recently? B. How soon will you be back? C. What are you going to do? D. Where did you hide? 9.－Can I borrow your camera for a week?－______________________. A. Sure, here you are B. Yes, you can borrow C. Yes, bring it with you D. It doesn’t matter 10.－Sorry, I have kept you waiting. －______________________. A. That’s all right B. I don’t care C. I’m sad D. No, not at all. Unit 2 1.－Mary, your dress is really beautiful. How is John?－ . A. Thank you very much. B. No, no, John is not bad. C. Thank you. He is fine. D. Don’t say that. It’s ugly. John is good. 2.－Do you mind telling me where you’re from?－ . A. Certainly. I’m from London. B. Sure. I was born in London. C. Not really, you can do it. D. Certainly not. I’m from London. 3.－May I see t he menu, please? I’ve been waiting an hour already.－ . A. That is the menu, sir. B. Yes, please go on. C. Here you are, sir. D. Of course, sir. 4.－I was worried about chemistry, but Mr. Brown gave me an A! － . A. Don’t worry about it. B. Congratulations! That’s a difficult course. C. Mr. Brown is very good. D. Good luck to you! 5.—Did Tom tell you to water the flowers? －___________________. A. No. And so did I B. No. And neither did I C. He did. And so I did D. He did. And so do I 6.—Shall we sit up here on the grass or down there near the water? — _____________. A. I’d rather stay here if you don’t mind B. Sorry, I don’t like neither