地区电网规划设计—毕业设计论文 (NXPowerLite)

1、核准通过，归档资料。 未经允许，请勿外传！ 摘摘 要要 本次设计的题目是“地区电网规划”,内容分为：电力网络方案的确定、 发电厂及变电站电气主接线设计、厂及所用电设计、短路计算、主要设备的 选择及校验、输电网络潮流分布的计算等部分。其中输电网络的功率与电压 分布及电器主接线的设计非常重要的，因为他们的可靠性、经济性和灵活性 直接影响着整个电网的可靠性、经济性和灵活性。还影响着厂用电设计、短 路计算、设备的选择校验等内容。本次设计的电力网络方案的确定及电气主 接线经过经济性比较后最终所选出的方案中选取可靠性比较高的为最后方案。 另外，短路计算部分也是本次设计的重要部分。他的准确性影响着设备的选

2、择及校验，也影响到整个网络的经济性与安全性。本次设计是本着可靠性和 安全性的原则来完成的。 关键词电力网 主接线 短路计算 潮流计算 6a*cz7h$dq8kqqfhvzfedswsyxty#槽形母线机械强度较好，载流量大， 集肤效应系数小， 一般用于 4000-8000a 配电装置中；管形母线集肤效应系数小， 机 械 强度高，管内可以通水和通风，可用于 8000a 以上的大电流母线，另 外， 由于圆管形表面光滑，电晕放电电压高，可用于 110 及以配电装置母线。 110kv 及以上高压配电装置，一般采用软导线。当采用硬导体时，宜用铝锰合金管形 导体。 (2).截面选择 软母线的截面选择： 按

3、照经济电流密度选择的母线都能满足导体长期发热条件，故按经济电流密度选择： s=imax/j imax-正常工作时的最大持续工作电流 j-经济电流密度。对应不同种类的导体和不同的最大负荷利用小时数 tmax，将 有不同取值。 硬母线的截面选择： 硬母线一般用于电压较低的配电装置中，所以，可以按最大持续工作电流选择导 线截面积： igmaxkiy iy-相应于某一母线布置方式和环境温度为+25oc 时的导体长期允许载流量。 k-温度修正系数。 (3) 热稳定校验 软母线不需热稳定的校验 硬母线的热稳定校验： smin=sqrt(qkks)/c c-热稳定系数。与导体材料及温度有关。 (4) 动稳定

4、校验 软母线无需动稳定校验。 硬母线的动稳定校验： 各种形状的硬母线通常都安装在支柱绝缘子上短路冲击电流产生的电动力将使 导体发生弯曲，因此，导体应按弯曲情况进行应力计算。110 及以上单根圆管母线上 产生的应力不能忽略不计。 多条母线的应力计算： 当母线由多条组成时，母线上最大机械应力由相间作用应力 xj和同相各条间的作用 力 tj合成，所以： max=xj+tj 1） 多条矩形母线的条间应力计算：由于同相条间距离很近，条件作用力大，为了 减少 tj，条间通常设有衬垫，为了防止同相各条矩形导体在条间作用力下产生弯曲 而互相接触，衬垫间允许的最大跨距-临界跨距 lcr，可由下式决定： lcr=

5、b4h/fb4 b,h-矩形导体的宽和高。 -系数，铜：双条为 1774，三条为 1355；铝；双条为 1003，三条为 1197。 fb-同相各条母线间单位长度的作用力 当同相为 2 条时： fb=2k12(0.5ish)2*10-7/2b=2.5k12i2sh*10-8/b(n/m) k12,k13-条 1，2 和条 1，3 的截面形状系数。 当同相为 3 条时，边条受力最大。 fb=fb1-2+fb1-3=8(k12+k13)i2sh*10-9/b(n/m) k12,k13-条 1，2 和条 1，3 的截面形状系数。 所选衬垫跨距应满足 lbu10.9un un为电压互感器额定一次线电压

6、，1.1和0.9是允许的一次电压波动范围，即 10% un。 4）二次电压：电压互感器二次电压，应根据使用情况，按下表选用所需的二次额 定电压。 电压互感器二次额定电压选择表 绕 组主 二 次 绕 组 附 加 二 次 绕 组 高压侧接入方式接于线电 压上 接于相电压 上 用于中性点 接地 用于中性 点不接 地 二次额定电压（v）100100/ 3 100100/3 5）准确等级 应在哪一准确等级下工作，需根据接入的测量仪表、继电器和自动装置等 设备对准确等级的要求确定。 用于电度表准确度不低于0.5级，用于电压测量，不应低于1级，用于继电 保护不应低于3级。（具体选择计算见毕业设计计算书） 。

7、 电压互感器的接线及使用范围 序号采 用 的 电 压 互 感 器使 用 范 围 1一个单相电压互感器测量某一相间和相对地电压的接线方式。 2 三个单相电压互感器用于表计和继电器的线圈接入相间电压 和高压侧中性点直接接地。 一个三相五柱式电压互感用于 3-5kv 电网中，可测量各相相间电 3器压和相对地电压。辅助绕组成开口三角 形 （2）电流互感器的选择 根据电力工程电气设计手册 1一次部分 p71 电流互感器的配置原则： 凡装有断路器的回路均应装设电流互感器，其数量应满足测量仪表、保护和自 动装置要求。 在未设断路器的下列地点也应装设电流互感器，发电机和变压器的中性点、出 口。 对直接接地系统

8、，一般按三相配置。对非直接接地系统，依具体要求按两相或三相配 置。 1）型式： 电流互感器的型式应根据使用环境条件和产品情况选择。 对于620kv屋内配电装置，可采用瓷绝缘结构或树脂浇注绝缘结构的电流互感器，对于 35kv及以上配电装置，一般用油浸箱式绝缘结构的独立式电流互感器，有条件时，应尽 量釆用套管式电流互感器。 2）参数选择： 电流互感器的二次侧额定电流有5a和1a两种，一般弱电系统用1a，强电系统用5a， 当配电装置距离控制室较远时，亦可考虑用1a。 a 一次额定电流的选择： 当电流互感器用于测量时，其一次额定电流应尽量选择的比回路中正常工作电流大 1/3左右，以保证测量仪表有最佳工

9、作，并在过负荷时，使仪表有适当的指示。 电力变压器中性点电流互感器的一次额定电流应按大于变压器允许的不平衡电流选 择，一般情况下，可按变压器额定电流的1/3进行选择。 当保护和测量仪表共用一组电流互感器时，只能选用相同的一次电流。 一次侧额定电流: i1nig.mas i1n为电流互感器原边额定电流，ig.mas为电流互感器安装处一次回路最大工作电流。 b 一次侧额定电压： unug ug为电流互感器安装处一次回路的工作电压，un为电流互感器额定电压。 c 准确等级的选择： 电流互感器准确等级的确定与电压互感器相同。需先知电流互感器二次回路所接测 量仪表的类型及以准确等级的要求，并按准确等级要

10、求最高的表计来选择。 用于电能测量的互感器准确级： 0.5功电度表应配用0.2级互感器；1.0级有功电度表应配用0.5级互感级；2.0 无功电度表也应配用0.5级互感器；2.0级有功电度表及3.0级无功电度表，可配用1.0 级互感器；一般保护用的电流互感器可选用3级，差动距离及高频保护用的电流互感器宜 选用d级，零序接地保护可釆用专用的电流互感器，保护用电流互感器一般按10%倍数曲线 进行校验计算。 d 热稳定校验: 电流互感器热稳定能力常以1s允许通过一次额定电流i1n来校验：(i1nkt) itdz kt为ct的1s热 稳定倍数； e动稳定校验： 内部动稳定可用下式校验： 2 i1nkdw

11、ich i1n-电流互感器的一次绕组额定电流（a） ich-短路冲击电4流的瞬时值（ka） kdw-ct的1s动稳定倍数 电流互感器的选择 5 52 25 5、高压熔断器的选择、高压熔断器的选择 (1)参数的选择： 高压熔断器应按所列技术条件选择，并按使用环境条件校验。熔断器是最简 单的保护电器，它用来保护电气设备免受过载电流的损害，屋内型高压熔断器在 变电所中常用于保护电力电容器配电线路和配电变压器，而在电厂中多用于保护 电压互感器。 (2)选择的技术条件： 电压： ug un 限流式高压熔断器不宜使用在工作电压低于其额定电压的电网中，以免 过电压而使电网中的电器损坏，故应为 ug=un 断

12、流容量：ich（或 i）ikd 式中 ich-三相短路冲击电流的有效值 ikd-熔断器的开断电流 说明：保护电压互感器的熔断器，只需按额定电压和断流容量选择，不必校验额 定电流。 （具体选择计算见毕业设计计算书） 。 5 52 26 6 限流电抗器选择及校验限流电抗器选择及校验 (1) 电抗器的作用 短路电流直接影响选择和安全运行，电力系统的短路电流随系统中单机容量和总 装机容量的加大而增长。在大容量发电厂和电力网中，短路电流可达很大数值，一致 使在选择发电厂和变电所的断路器及其它配电设备时面临困难，要使配电设备能承受 短路电流的冲击，往往需要提高容量等级，这不仅使投资增加，甚至还可能因断流容

13、 量不足而选不到合乎要求的断路器。所以发电厂和变电所的接线设计中，常需采用限 制短路电流的措施，减小短路电流，以便采用价格较便宜的轻型电器及截面较小的导 线。这时就应当选取限流电抗器。 (2) 限流电抗器应按下列技术条件选择： 电压：ugun ug-电网工作电压 电流：ig.maxin ig.max-最大持续工作电流 动稳定：ichidw 电抗器的动稳定电流 ich -电抗器后三相短路电流冲击值 热稳定：i2tdzit2t 电抗百分值： 普通电抗器按以下条件选择： 1） 为将短路电流限制到要求值 i”.则应满足： xk（%）（ib/i”-x，）inub/ibun100 xk（%）电抗器百分电抗

14、值。 ib、ub基准电流（a） ，基准电压（kv） in、un电抗器的额定电流，额定电压。 x，以 ib、ub为基准值计算至所选用电抗器前的网络电抗标幺值。 5 52 27 7 避雷器的选择避雷器的选择 避雷器是一种保护电器，用来保护配电变压器，电站和变电所等电器设备的 绝缘免受大气过电压或某些操作过电压的危害。大气过电压由雷击或静电感应产 生；操作过电压一般是由于电力系统的运行情况发生突变而产生电磁振荡所致。 避雷器有两种： (1)阀型避雷器 按其结构的不同，又分为普通阀型避雷器和磁吹阀型避雷器； (2)管型避雷器 利用绝缘管内间隙中的电弧所产生的气体把电弧吹灭。用于 线路作为防雷保护。 阀

15、型避雷器应按下列条件选择： a 额定电压：避雷器的额定电压应与系统额定电压一致。 b 灭弧电压：按照使用情况，校验避雷器安装地点可能出现的最大的导线对地 电压，是否等于或小于避雷器的最大容许电压（灭弧电压）；在中性点非直接接地的电 网中应不低于设备最高运行线电压。在中性点直接接地的电网中应取设备最高运行线电 压的 80%。（具体选择计算见毕业设计计算书） 。 第六章第六章 输电网络的潮流计算输电网络的潮流计算 目的电力系统潮流计算是电力系统设计及运行时不可缺少的基本计算。在设计时潮 流计算的是为评价网络方案，选择导线及变电所主要设备的规格，并为选用调压装置， 无功补偿设备及其配电提供依据，为稳

16、定计算分析提供原始条件；对运行部门，主要是 为指定良好的运行方式。 潮流计算时，系统备用容量的分配应注重能源的合理利用和系统的安全，经济运行。 （1）功率损耗和电压损失的计算 当功率 pi+jqi通过阻抗 r+jx 时，所产生的功率损耗为： p+jq=r u qp i ii 2 22 +jx u qp i ii 2 22 产生的电压降落的纵分量ui和横分量分别为： ui= i ii u xqrp ui= i ii u rqxp 式中 r、x分别为线路或变压器的电阻，电抗， pi、qi、ui分别为线路或变压器按潮流方向的始端（或末端） 有功功率 mw,无功功率 mvar，电压 kv。 设 pi、

17、qi、ui均为始端数据，利用以上两式可计算出ui及ui 则末端电压向量为： u2=(u1-ui)-jui 若已知末端数值 p2、q2、u2，则始端的电压向量为 u1=(u2-u2)-ju2 对于线路，始末两端的电压向量的相角差，称为功率角。电压向量差成为电压降 落，始末端的电压数值称为电压损失。 （2） 环形网络潮流分布的计算 首先将环网在任一点处打开，称为二端网络，暂不记功率损失，应用功率平衡原理， 以某一点为中心，可计算出环网内部的自然分布功率，并得到功率分点。然后，假功率 分点处电压为额定值或某一适当值，并从此点开始，计算线路损耗功率和电压一般取无 功功率分点作为计算起点。 若环形网络有

18、不同电压等级组成，则应采用归算至同一电压等级的阻抗进行上述 计算。 （3）调压计算 电力系统各级网络的电压偏差必须控制在一定范围内，为保证这一要求，必须采取 适当措施，如： 调整发电机端电压 改变变压器分接头开关位置 调解无功补偿功率 改变电力系统运行方式。 system choice operational requirements all power station operated by the gegb have their operational requirements set down by the gegbs system planning department in the

19、station development particulars (sdps). the choice pf electrical system will be influenced by these requirements, the major aspects of which are discussed below: (a) most nuclear plant is operated in a base load regime especially as the output cost/kw from nuclear plant is cheaper than most fossil-f

20、uelled plant. coal-fired plant is, however, more adaptable to following the load demand curve. clearly the electrical system must facilitate the operational flexibility where this is required. in nuclear power plant the overriding consideration is one of nuclear safety, and this is always uppermost

21、in the designers mind .the system chosen for nuclear plant must have an inherent ability to be configured in the most appropriate form for post-trip cooling, bearing in mind the alternative supply choices available. (b) the electrical system is required by the sdps to be designed such that a single

22、fault will not cause the loss of more than one generating unit. this reflects the need to limit the generation loss to the system due to single faults. the connections to the grid site must also be examined to ensure that a single system or substation fault will not cause more generation loss than t

23、he system can tolerate. this is of particular concern in situations where more than one station is connected to a common sunstation. (c)power plant designed and installed in the early 1960s assumed that grid loss could be tolerated and that the transmission system would not totally collapse. subsequ

24、ent events showed that a condition could occur which cause cascade tripping, i.e., power stations being tripped in an attempt to supply loads in excess of rating. this led to power plant being specified which could be started up in the absence of external grid supplies. for the 500mw units, a twin a

25、von (25-28mw) gas-turbine generating set was used, but this was superseded at the later stations having 660mw units by twin olympus (35mw) sets because of the need for a large rating. the generator output voltage in all cases was nominally 11kv and the gas turbines were connected to the 11kv unit bo

26、ards. gas-turbine generators were installed for duties summarized as follows: *black station starting the gas turbine is run-up and closed onto a dead busbar. synchronizing is only required for regular teating in parallel with the grid derived supplies. gas turbines would normally be connected to th

27、e unit board. *peak lopping as the gas-turbine generators have to be paralleled with the grid, automated synchronizing is provided. gts would normally be connected to the unit board when the associated main unit is generating or via the unit/station board interconnector to the station transformer wh

28、en the main unit is shutdown. *frequency support the gas-turbine generator responds to falling frequency, start, and is closed onto the busbar, this is specified to occur at frequencies down to 40hz and auto synchronizing is required. *supplies to essential equipment supplies to essential drives suc

29、h as generator seal oil, barring gear and, if a nuclear plant, electrical supplied to the post-trip cooling equipment. the choice of rating, the number of gas turbines and their connection to the auxiliaries system, are all influenced by the given in the duty definition to the requirements for manua

30、l synchronizing, and for the inclusion of centralized control. the first agr nuclear stations were fitted with single olympus gas turbines at 17.5 mw rating but these were for nuclear safety needs primarily, and were not intended for black start purposes, although some peak lopping duties were perfo

31、rmed. (d)the plant must be design to meet the voltage and frequency limits set by the system. typically these are as follows: all electrical plant must be capable of maintaining full cmr output within the range 49.5-51hz.form 49.5 to 47hz the output may be prorate with frequency, but operation below

32、 48hzwill not be for longer than 15 minutes. frequency excursions between 51-52.5hz may be experienced, but these will only be for short periods. the hv system voltage to which the power station is connected is normally 400kv or 275kv, with typical limits of: 400kv , 5 275kv ,10 the electrical auxil

33、iaries system must be designed to recognize these variations, as well as taking into account the drop in voltage through the system due to varying load and running conditions. most modern conventional power plants have three main nominal voltage levels viz, 11kv, 3.3kv and 415v. the design limits of

34、 these voltage levels are typically form +6 to -10 with -20 under motor starting conditions. the voltage at all nominal levels is maintained by means of optimizing the transformer tap positions, such that the 415v drive most remote from the primary(11kv) busbar is the worst condition, e.g., when sta

35、rting. a check of the voltage profile under light load conditions is also made to ensure that the system is not overstressed. the design stage voltage profile is verified by system studies which model the system using interactive computer programs. the studies will of course need updating at a later

36、 date when all the manufacturers data is known. reliability of main and standby plant the design of the electrical system should, in general, reflect the requirements of the mechanical plant and should not reduce its reliability. where important mechanical system are provided with redundancy, the el

37、ectrical supplies should also be supplied electrically form independent sources, via segregated supply routes. for nuclear power stations, the mechanical and electrical plant may well require segregation, and will ultimately be segregated into independent functional trains. this approach has proved

38、to be the most robust system of providing defense against the whole range of credible faults, verified by probalistic analysis techniques. the use of diverse equipment in independent functional trains also benefits by reducing the impact of common mode and common cause failures. these techniques can

39、 be employed to provide the level of reliability required for the systems which are associated with nuclear plant. the reliability of a system will be analysed by the use of probalistic analysis techniques. to obtain a meaningful answer, the computer reliability must be assessed. this is not always

40、easy form a historical point of view, when computer may have been in use only for a few years. however, by using equipment which has been rigorously and systematically tested, a certain degree of confidence may be obtained form the attributed component failure rates are considered not only for norma

41、l conditions but also for abnormal conditions both naturel and following major plant disruptions. this includes levels, and also missile impact. equipment is classified into items which are required to withstand seismic and environmental conditions and those which are not. again verification is achi

42、eved by subjective testing. the choice of system will depend on the reliability required of it and the availability of suitable components. the use of proven equipment, which has demonstrated a satisfactory performance under varying conditions, will also support the predicted reliability of the syst

43、em. new designs of equipment should be avoided in essential system, unless they have been developed and tested to demonstrate standards of technical requirement at least as high as those claimed in the system design. the reliability of electrical system is also enhanced by ensuring that designs foll

44、ow the design principles. economics the choice of electrical system for a particular power station project will be influenced by several economic factors, the main aspects of which are discussed below. capital cost the initial capital cost of an electrical scheme can be estimated form a cost analysi

45、s of the various components proposed. this can be achieved using data form many source, for example: contract prices of similar equipment on other (preferably recent) project. budget prices form possible suppliers or manufactures. standard cost estimating databases. to enable a true comparative esti

46、mate to be made, all prices and costs must be related to a common price basis date. any adjustment must be made using standard factors. where designs are not finalized, a judgement must be made and an estimated cost attributed to it in the form of provisional sums, to allow for any variation from th

47、e base design. the cegb employs a standard capital cost breakdown method for estimating new projects, where costs are allocated to particular coded plant areas. there costs are reviewed on a regular basis (usually annually) and updated as and when more firm information becomes available, e.g., tende

48、r prices or contract sums. in this way, close cost control can be applied to ensure that the project remains within the budget. in the early stages of a project, when designs are still subject to change, it is difficult to finalise the final electrical system due to the lack of confirmed information

49、 regarding the mechanical plant it is required to supply. however, by use of the estimating techniques mentioned above , it is possible to compare one proposed scheme with another for a particular duty so that the most cost effective scheme may be chosen. transformer losses transformers associated w

50、ith modern power stations are of ratings up to 60mva for unit and station transformers. although designs are available which minimize the losses, then are still significant when taken over the life of the station? it is therefore present practice to include an estimate of the capitalized losses over

51、 the station life in the station cost estimates. due regard to this element must be exercised in the choice of the electrical system. consequential costs (connection to the national grid) to connect the power station into the national grid will require extra circuits to be used or provided at the tr

52、ansmission substation adjacent to the proposed site. in general, most substations have been in existence new generating plant to the existing system. the cost of the generation circuits, associated circuit-breakers, isolators, busbars and civil costs are attributed to the power station capital estim

53、ates. the costs for the remaining ehv equipment are attributed to the transmission account but, nevertheless, alternative configurations will be examined to arrive at the most cost effective scheme. some of the options which are likely to require examination are as follows: * grid system voltage it

54、is s policy to connect all modern new generating plant to the 400kv system. the facilities available at the substation will determine whether a new 400kv substation would be required or the exiting equipment extended. it is also a policy to construct new 400kv substations with metalclad gas-insulate

55、d (sf6) equipment, and if at coastal or polluted sites to enclose them within a building. *station transformer primary voltage the station transformers may be connected at 132kv, 275kv or 400kv. the choice depends on several factors. the most economic option will normally be a 132kv connection. the

56、electrical load on the station transformers imposed by modern power plant is considerable, it may therefore be necessary to uprate the 132kv substation by the addition of an extra supergrid (400/132kv) transformer to support the capacity required. this reinforcement of the 132kv system, if required

57、only to meet the new power station load, may make this scheme economically less attractive. also the position of 132kv substation may require very long cable connections, again adversely affecting the scheme economics. cost analyses showing these considerations will demonstrate which the most econom

58、ic proposal is, but the final decision will be based on a combination of economic, technical and operational considerations. whilst the cegb policy is to use proven and tested plant, development work is often required to meet a need which has hitherto not been identified. the cost of this developmen

59、t work may be borne by the project and in that case a capital sum is included in the project estimates. the choice of system design may be influenced by the need to develop a particular piece of plant rather than use an existing alternative. in this case, a justification would have to be made to dem

60、onstrate the technical superiority compared with the cost of the development work. sometimes development work is required because the previous equipment is not longer available, or is no longer manufactured, and there is not attributable to a particular project and would be funded form a general dev