正确的舆论导向——关于铁塔在电线覆冰后为什么容易倒塌的原因� ZZ from BMY

发信人: bluesky (令狐冲 嘿嘿！), 信区: XJTUeec
标 题: 正确的舆论导向——关于铁塔在电线覆冰后为什么容易倒塌的原因�
发信站: 兵马俑BBS (Tue Jan 29 12:43:44 2008), 本站(bbs.xjtu.edu.cn)

编者按：针对目前一些社会人员甚至个别涉电工作者，对覆冰倒塔的一些不正确认识现象，从专业角度讲一讲相关常识，尽量客观反映当前电力部门的工作，让所有人做出自已的正确判断，供参考。

1、基础知识首先讲电力线路的杆塔，线路要架空就必须有两种杆塔，即一是直线塔、另一种是耐张塔，简单的比喻就是你要晒衣裳拉一根线，两端要固定在墙上，中间用竹杆撑起。好了，直线塔就有了，竹杆就是直线塔，其作用就是挑起导线，一般只承受导线的自重，专业讲就垂直荷载。
同时耐张塔也有了，即是晒衣裳固定的墙，所以电力线路线路最易出危险的是耐张塔，因为导线受张力架空后，沿导线纵向拉起的力全部挂在耐张塔上，即耐张塔要承受电力线路架空后的张力载荷，也就是要当成墙壁一样承受导线的拉力。

2、专业名词导线的标称截面，400/35，即400表示导线的铝股部分横截面积为400平方mm，35表示钢芯部分横截面积为35平方mm。当 前500kV高压送电线路多为该型导线，然后每相导线有4根，一条线路为3相导线，共12根导线，还有两根避雷线。一般线路就是这样的导线结构，架空在天 上的共有14根线。
（1）导线的自重，1米400/35导线的自重是1.511kg
（2）按南方多年的气象条件，设计时冰厚10mm，导线上履10mm厚冰后的增加重量是：1.04kg.计算式是y2=〔3.14*（d/2+b)^2-3.14*(d/2)^2〕*1000*0.9 b是冰厚，d是导线直径，A是导线截面积，冰密度0.9
（3）由此：每一米导线的上加冰后的重量是：1.511+1.04＝2.551kg。
（4）耐张塔正常设计时应承受的张力G是：2.55*1000米*4根子导线*3相＝30.6吨。 取平均水平档距1000米 （多数为500～700米，考虑山区的连续上山档等因素取1000米）耐张塔的高度一般在20米左右。此30吨纵向拉力挂在塔上，对基础的扭力力距为20 米，基础即按此不利的受力条件进行选取。耐张塔身要承受的扭力即为抗拒30吨的扭力力矩。
（5）而当履冰为 50mm厚，代入计算式：y2＝10.85；G＝（10.85+1.511）*1000*4*3＝148.3吨。
当冰厚为100mm时，代入计算式：y2＝35.83；G＝（35.839+1.51）*1000*4*3＝448.2吨。
（6）由此可见：50mm的冰产生的张力是10mm冰的148.3/30.612＝ 4.85倍。
100mm的冰产生的张力是10mm冰的448.2/30.612＝16.6倍。
虽然线路设计取了2.5倍的安全系数。但是由于冰厚产生的荷载是平方关系的增长，耐张塔不可能按几十年不遇的天气条件来设计。
如果为了抗拒100mm冰的而设计耐张塔，其塔身强度和基础强度都是不可想像的。在线路工程的造价中，铁塔投资占20％。而三峡到上海的线路2000公 里，塔量为2000基以上，总造价为40亿元。单位造价为200万元/公里，如要每基塔均增加投资去抗衡50～100mm冰，电力线路的总体投资翻10倍 左右。即达到400亿，按此推算，当前电力建设每年建设电力线路均在5000公里左右。按10倍的关系，即光电力线路建设即达到1000个亿。而一个国家 级的三峡工程也不过2000亿元，
另外，电网投资均由电力企业自行投资，完全是为了保履冰而这样投资是不合理的，也不经济的，将会造成极大的浪费。

质疑之一的解释：为何导线不断而塔倒的问题，这很好理解，这是因为耐张塔要承受不利的力矩效应（塔高20米），而导线只单纯的承受纵向张力。在所 有的导线中心均用钢绞线进行承力，在履冰时，首先崩溃的一定是耐张塔，再才是倒塔的冲击力挣断导线。这就好比用绳子拴到一棵树上，用力扯绳子，断掉的一定 是树根，因绳子只受纵向拉力，故先断的是树，树断后，对绳子产生冲击，再断绳子。

质疑之二的解释：北方未倒塔的原因是：天气干冷，塔身不会凝冰，导线上只是有附着积雪，没有大量挂冰，而且在设计时冰厚就取得大， 般在30mm左右。而湖南、贵州的事故中，导线上全部凝冰达50～100mm，塔身及绝缘子上全结成了水桶。这样多的额外荷载均由铁塔来承受，远远超出了 国家规定的铁塔使用条件。不倒塔才不正常。说句极端的话，按100mm冰设计的定型塔图，估计国家当前还没有可选用的定型塔呢！


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※ 来源:．兵马俑BBS http://bbs.xjtu.edu.cn [FROM: 61.144.49.122]

※ 修改:．bluesky 于 Jan 29 12:44:36 修改本文．[FROM: 61.144.49.122]

10 Secrets to Success zz

1. How You Think is Everything.

Always be positive. Think Success, not Failure. Beware of a negative environment.

This trait has to be one of the most important in the entire list. Your belief that you can accomplish your goals has to be unwavering. The moment you say to yourself “I can’t…”, then you won’t. I was always given the advice “never say I can’t” and I’d like to strike those words from the dictionary.

I’ve found that from time-to-time my attitude waivers. A mentor of mine once said “it’s ok to visit pity city, but you can’t stay and there comes a time when you need to leave”. Positive things happen to positive people.

2. Decide upon Your True Dreams and Goals: Write down your specific goals and develop a plan to reach them.

Write down my dreams and goals? Develop a plan to reach them? You mean like a project plan? Yes, that’s exactly what this means. You may have heard the old adage: A New Years resolution that isn’t written down is just a dream, and dreams are not goals.

Goals are those concrete, measurable stepping stones of achievement that track your progress towards your dreams. My goal is to start a second career as a freelance writer – what are your goals?

3. Take Action. Goals are nothing without action.

Be like Nike and “Just do it”. I took action by reaching out and started writing. Every day I try to take some action towards my goals. It may be small, but it’s still an action. Have you taken action towards your goals?

4. Never Stop Learning: Go back to school or read books. Get training & acquire skills.

Becoming a life long learner would benefit us all and is something we should instill in our kids. It’s funny that once you’re out of school you realize how enjoyable learning can be. What have you learned today?

5. Be Persistent and Work Hard: Success is a marathon, not a sprint. Never give up.

I think every story of success I read entails long hard hours of work. There is no getting around this and there is no free lunch. But, if you’re working towards something that you’re passionate about, something you love – then is it really work?

6. Learn to Analyze Details: Get all the facts, all the input. Learn from your mistakes.

I think you have to strike a balance between getting all the facts and making a decision with incomplete data – both are traits of successful people. Spend time gathering details, but don’t catch ‘analysis paralysis’.

7. Focus Your Time And Money: Don’t let other people or things distract you.

Remain laser focused on your goals and surround yourself with positive people that believe in you. Don’t be distracted by the naysayer’s or tasks that are not helping you achieve your goals.

8. Don’t Be Afraid To Innovate: Be different. Following the herd is a sure way to mediocrity.

Follow through on that break-out idea you have. Ask yourself “What would I do if I wasn’t afraid?”

9. Deal And Communicate With People Effectively: No person is an island. Learn to understand and motivate others.

Successful people develop and nurture a network and they only do that by treating people openly, fairly and many times firmly. There is nothing wrong about being firm – just don’t cross the a-hole line. How do you deal with people?

10. Be Honest And Dependable: Take responsibility, otherwise numbers 1 – 9 won’t matter.

7 habits of highly ineffective people

1. not showing up
2. procrastinating half the day
3. do not do actually the things most important right now
4. thinking too much
5. seeing negative and downside of everything
6. cling to your own thoughts and being closed to the outside influence
7. constantly information overload

from http://www.positivityblog.com/index.php/2007/09/05/7-habits-of-highly-ineffective-people/