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雷电防护知识

   在(zai)我国,每年因(yin)雷击造成的人(ren)员(yuan)伤亡估计3500~4000人(ren),财产损失(shi)估计在(zai)70~100亿元左右。因(yin)此,在(zai)了解防雷产品之前,我们不妨先对(dui)雷电保护知识(shi)作(zuo)一(yi)些了解,以便(bian)在(zai)选(xuan)购和使用中有必要的正确认识(shi)。

   

一、雷击(ji):

    雷(lei)是大气中的放电现象(xiang),雷(lei)击(ji)主要有(you)2种:直(zhi)击(ji)雷(lei)和感(gan)应(ying)雷(lei)。其中直(zhi)击(ji)雷(lei)只占雷(lei)击(ji)的10%左右(you),危害范围比较小,在CATV系统和网络中,常用避(bi)雷(lei)针、避(bi)雷(lei)线和避(bi)雷(lei)网来防(fang)护(hu);而危害**的感(gan)应(ying)雷(lei),占雷(lei)击(ji)率(lv)的90%,危害范围广,难以有(you)效进行(xing)防(fang)护(hu),绝(jue)大部分电子装置主要是感(gan)应(ying)雷(lei)雷(lei)击(ji)而损坏的。

    1、直击(ji)雷(lei)(lei)(lei)的(de)(de)(de)产生(sheng)与危害(hai)(hai)(hai):直击(ji)雷(lei)(lei)(lei)是(shi)(shi)(shi)带电(dian)(dian)(dian)(dian)(dian)云(yun)(yun)层(ceng)和大(da)地之间的(de)(de)(de)放(fang)电(dian)(dian)(dian)(dian)(dian)所造成(cheng)(cheng),在(zai)形成(cheng)(cheng)雷(lei)(lei)(lei)云(yun)(yun)的(de)(de)(de)程(cheng)(cheng)序中(zhong),部分云(yun)(yun)层(ceng)显(xian)正(zheng)电(dian)(dian)(dian)(dian)(dian)荷(he)(he)而(er)使(shi)电(dian)(dian)(dian)(dian)(dian)位逐渐升(sheng)高(gao);另一些云(yun)(yun)层(ceng)则带负电(dian)(dian)(dian)(dian)(dian)荷(he)(he),当2种云(yun)(yun)层(ceng)接近时(shi)一定程(cheng)(cheng)度时(shi)便发生(sheng)迅速(su)强(qiang)烈的(de)(de)(de)放(fang)电(dian)(dian)(dian)(dian)(dian),放(fang)电(dian)(dian)(dian)(dian)(dian)时(shi)的(de)(de)(de)温度可高(gao)达2万度,空(kong)气受热急剧膨(peng)胀,每次放(fang)电(dian)(dian)(dian)(dian)(dian)大(da)约在(zai)几微秒内释放(fang)相当大(da)的(de)(de)(de)能量。当雷(lei)(lei)(lei)云(yun)(yun)很低(di),周围又缺少其它异性(xing)电(dian)(dian)(dian)(dian)(dian)荷(he)(he)的(de)(de)(de)雷(lei)(lei)(lei)云(yun)(yun)时(shi),此时(shi)便会(hui)在(zai)建筑(zhu)物(wu)或地面(mian)感应出异性(xing)电(dian)(dian)(dian)(dian)(dian)荷(he)(he),致使(shi)带电(dian)(dian)(dian)(dian)(dian)云(yun)(yun)层(ceng)向地面(mian)或建筑(zhu)物(wu)放(fang)电(dian)(dian)(dian)(dian)(dian),这(zhei)种雷(lei)(lei)(lei)电(dian)(dian)(dian)(dian)(dian)就(jiu)是(shi)(shi)(shi)直击(ji)雷(lei)(lei)(lei),它对建筑(zhu)物(wu)和人、畜、树(shu)木等(deng)危害(hai)(hai)(hai)巨大(da),由于此时(shi)放(fang)电(dian)(dian)(dian)(dian)(dian)电(dian)(dian)(dian)(dian)(dian)流(liu)可达到几十(shi)甚(shen)至(zhi)几百(bai)千安,放(fang)电(dian)(dian)(dian)(dian)(dian)时(shi)间极短,简直无法防避(bi),常用的(de)(de)(de)避(bi)雷(lei)(lei)(lei)针方(fang)式是(shi)(shi)(shi)目(mu)前减(jian)少直击(ji)雷(lei)(lei)(lei)损(sun)害(hai)(hai)(hai)的(de)(de)(de)比较好的(de)(de)(de)防护方(fang)式,但(dan)是(shi)(shi)(shi)使(shi)用者在(zai)实(shi)际工(gong)作中(zhong)常发现直击(ji)雷(lei)(lei)(lei)过(guo)后,许多电(dian)(dian)(dian)(dian)(dian)子(zi)装置仍然有较大(da)的(de)(de)(de)损(sun)害(hai)(hai)(hai),大(da)多数是(shi)(shi)(shi)烧毁(hui)保险器件、电(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)变压(ya)器、整流(liu)器件、甚(shen)至(zhi)集成(cheng)(cheng)电(dian)(dian)(dian)(dian)(dian)路等(deng)。这(zhei)是(shi)(shi)(shi)什么原因造成(cheng)(cheng)的(de)(de)(de)呢?这(zhei)就(jiu)是(shi)(shi)(shi)感应雷(lei)(lei)(lei)造成(cheng)(cheng)的(de)(de)(de),它通过(guo)CATV系统的(de)(de)(de)电(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)转载(zai)入装置造成(cheng)(cheng)损(sun)害(hai)(hai)(hai)。

    2、感(gan)(gan)(gan)(gan)应(ying)(ying)(ying)(ying)(ying)雷(lei)(lei)的(de)(de)产生(sheng)与(yu)危害:感(gan)(gan)(gan)(gan)应(ying)(ying)(ying)(ying)(ying)雷(lei)(lei)是由(you)静电(dian)(dian)(dian)(dian)(dian)(dian)(dian)抗(kang)器应(ying)(ying)(ying)(ying)(ying)和雷(lei)(lei)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)产生(sheng)的(de)(de)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)磁(ci)感(gan)(gan)(gan)(gan)应(ying)(ying)(ying)(ying)(ying)两种(zhong)原(yuan)因(yin)所造(zao)成(cheng)(cheng)的(de)(de),当带电(dian)(dian)(dian)(dian)(dian)(dian)(dian)雷(lei)(lei)云靠近(jin)输电(dian)(dian)(dian)(dian)(dian)(dian)(dian)线路(lu)时,线路(lu)上面会感(gan)(gan)(gan)(gan)应(ying)(ying)(ying)(ying)(ying)出(chu)异性电(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he),这些异性电(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)被雷(lei)(lei)云电(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)束缚着(zhe),当雷(lei)(lei)云对附近(jin)字段或接闪器放电(dian)(dian)(dian)(dian)(dian)(dian)(dian)时,其电(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)迅(xun)速中和,而此(ci)时输电(dian)(dian)(dian)(dian)(dian)(dian)(dian)线路(lu)上的(de)(de)被束缚电(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he)便成(cheng)(cheng)为自(zi)由(you)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)荷(he),形成(cheng)(cheng)局部感(gan)(gan)(gan)(gan)应(ying)(ying)(ying)(ying)(ying)高(gao)(gao)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei),这种(zhong)感(gan)(gan)(gan)(gan)应(ying)(ying)(ying)(ying)(ying)高(gao)(gao)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)位(wei)发生(sheng)在(zai)低压架空线路(lu)时最高(gao)(gao)可达100KV;在(zai)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)讯线路(lu)上可达40—60KV。而且它可以顺延线路(lu)进入各种(zhong)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)子装(zhuang)置造(zao)成(cheng)(cheng)损坏(huai),而损坏(huai)的(de)(de)主要原(yuan)因(yin)是电(dian)(dian)(dian)(dian)(dian)(dian)(dian)磁(ci)感(gan)(gan)(gan)(gan)应(ying)(ying)(ying)(ying)(ying)。电(dian)(dian)(dian)(dian)(dian)(dian)(dian)磁(ci)感(gan)(gan)(gan)(gan)应(ying)(ying)(ying)(ying)(ying)是雷(lei)(lei)击后巨(ju)大的(de)(de)雷(lei)(lei)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)在(zai)周围空间(jian)产生(sheng)交变磁(ci)场(chang)引起(qi)雷(lei)(lei)场(chang)附近(jin)装(zhuang)置感(gan)(gan)(gan)(gan)应(ying)(ying)(ying)(ying)(ying)出(chu)高(gao)(gao)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)压损坏(huai)装(zhuang)置。感(gan)(gan)(gan)(gan)应(ying)(ying)(ying)(ying)(ying)雷(lei)(lei)的(de)(de)雷(lei)(lei)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)波(bo)(bo)(bo)头(由(you)零至幅直(zhi))一(yi)般(ban)祇有几秒,波(bo)(bo)(bo)尾也祇有几十微(wei)秒,但感(gan)(gan)(gan)(gan)应(ying)(ying)(ying)(ying)(ying)雷(lei)(lei)的(de)(de)雷(lei)(lei)电(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)却包含丰(feng)富的(de)(de)高(gao)(gao)次谐波(bo)(bo)(bo),它的(de)(de)基波(bo)(bo)(bo)频率大约等(deng)于几十千赫(he)。因(yin)此(ci),对感(gan)(gan)(gan)(gan)应(ying)(ying)(ying)(ying)(ying)雷(lei)(lei)的(de)(de)防(fang)护问题一(yi)直(zhi)困扰着(zhe)各类电(dian)(dian)(dian)(dian)(dian)(dian)(dian)子装(zhuang)置的(de)(de)使用(yong)者(zhe),特别是在(zai)野外环境下使用(yong)的(de)(de)各种(zhong)系(xi)统网(wang)络(luo)的(de)(de)使用(yong)者(zhe),如电(dian)(dian)(dian)(dian)(dian)(dian)(dian)力线路(lu)、通讯线路(lu)、有线电(dian)(dian)(dian)(dian)(dian)(dian)(dian)视线路(lu)、监控系(xi)统线路(lu)、宽(kuan)带数(shu)据(ju)网(wang)络(luo)系(xi)统等(deng),因(yin)而最易受感(gan)(gan)(gan)(gan)应(ying)(ying)(ying)(ying)(ying)雷(lei)(lei)的(de)(de)损害。

二、雷(lei)电的(de)破坏(huai)原(yuan)理

    雷电流的机械(xie)力作用能使被(bei)击(ji)物体(ti)遭受破坏,雷电的破坏原理主要表现(xian)在下述几个方面(mian):

    1、雷(lei)(lei)电(dian)(dian)流(liu)热(re)效(xiao)应破(po)坏原理:闪电(dian)(dian)击中地(di)面物(wu)体(ti),闪电(dian)(dian)电(dian)(dian)流(liu)产生(sheng)(sheng)焦耳(er)-楞(leng)次(ci)热(re)效(xiao)应,虽然电(dian)(dian)流(liu)峰值(zhi)很(hen)高,但作用的时(shi)间(jian)(jian)却很(hen)短,只(zhi)能产生(sheng)(sheng)局(ju)部瞬时(shi)高温(wen),强大的雷(lei)(lei)电(dian)(dian)流(liu)通过(guo)被雷(lei)(lei)击的物(wu)体(ti)时(shi)会产生(sheng)(sheng)很(hen)高的温(wen)度(du)(du)而发生(sheng)(sheng)溶化(hua)、汽化(hua)或燃(ran)(ran)烧的现象,可以使较(jiao)小体(ti)积的金属溶化(hua)。在回击阶段(duan),雷(lei)(lei)云对(dui)地(di)放电(dian)(dian)的峰值(zhi)可达数(shu)倍(bei)105A以上(shang)(shang),瞬间(jian)(jian)功率(lv)可达1011W以上(shang)(shang),在这(zhei)瞬间(jian)(jian),它将在其通道上(shang)(shang)造成强加热(re)效(xiao)应,放电(dian)(dian)通道中空气温(wen)度(du)(du)瞬间(jian)(jian)可升到30000度(du)(du)以上(shang)(shang),因(yin)此在通道上(shang)(shang)遇到可燃(ran)(ran)物(wu)质时(shi),便(bian)会产生(sheng)(sheng)火灾。

    2、雷电(dian)流冲击(ji)波(bo)的(de)破坏原理(li):由于(yu)雷电(dian)通道中空(kong)气(qi)受(shou)热急剧膨胀(zhang),并以超(chao)声速度(du)(du)向四周扩(kuo)散,其(qi)外(wai)围附(fu)近(jin)的(de)冷空(kong)气(qi)被强烈压(ya)(ya)(ya)缩(suo)形成“激(ji)(ji)波(bo)”。被压(ya)(ya)(ya)缩(suo)空(kong)气(qi)的(de)外(wai)界(jie)称为“激(ji)(ji)波(bo)波(bo)前(qian)”。“激(ji)(ji)波(bo)波(bo)前(qian)”到(dao)达(da)的(de)地(di)方,空(kong)气(qi)密(mi)度(du)(du)、压(ya)(ya)(ya)力和温度(du)(du)都会(hui)突然增加。“激(ji)(ji)波(bo)波(bo)前(qian)”过后,该(gai)区域内空(kong)气(qi)压(ya)(ya)(ya)力下降,直到(dao)低于(yu)大气(qi)压(ya)(ya)(ya)力。这种“激(ji)(ji)波(bo)”在(zai)空(kong)气(qi)中传播(bo),会(hui)使附(fu)近(jin)的(de)建(jian)筑物受(shou)到(dao)破坏,人(ren)和牲畜受(shou)到(dao)伤(shang)害,如同(tong)炸(zha)药在(zai)爆炸(zha)时(shi)对(dui)附(fu)近(jin)建(jian)筑物、人(ren)和牲畜受(shou)到(dao)伤(shang)害一(yi)样。雷云在(zai)放(fang)电(dian)后收缩(suo)的(de)过程中,由于(yu)雷电(dian)的(de)突然收缩(suo),还会(hui)产生次(ci)声波(bo),它同(tong)样对(dui)人(ren)、牲畜有(you)伤(shang)害作用。

    3、雷电流(liu)的(de)(de)电动力(li)效应的(de)(de)破坏原理:由于(yu)雷电流(liu)的(de)(de)峰值很大,作(zuo)用时间(jian)很短,其(qi)产生的(de)(de)电动力(li)具(ju)有(you)冲(chong)力(li)特性。这种

电动力的(de)冲(chong)力对金属导体有较大(da)的(de)破坏性。

    4、雷电(dian)(dian)的(de)静电(dian)(dian)感应(ying)和电(dian)(dian)磁感应(ying)的(de)破(po)坏(huai)原(yuan)理:闪电(dian)(dian)在(zai)回击通道及(ji)其贴近处产生强大(da)的(de)机械(xie)效应(ying)、加(jia)热(re)效应(ying)外(wai),同时(shi)也产生可(ke)波及(ji)较远处的(de)电(dian)(dian)磁效应(ying),这(zhei)种(zhong)电(dian)(dian)磁波的(de)危(wei)害性(xing)导致了大(da)量(liang)的(de)电(dian)(dian)子设备的(de)损坏(huai)和中(zhong)断工作。

   (1)静电(dian)(dian)(dian)感(gan)(gan)应(ying)(ying)(ying)(ying):当空间(jian)有带电(dian)(dian)(dian)的(de)(de)(de)雷(lei)云出现时(shi),雷(lei)云下的(de)(de)(de)地(di)面(mian)及建(jian)筑物(wu)等,都由于(yu)静电(dian)(dian)(dian)感(gan)(gan)应(ying)(ying)(ying)(ying)的(de)(de)(de)作(zuo)用而(er)带上(shang)相(xiang)反的(de)(de)(de)电(dian)(dian)(dian)荷(he)。在(zai)雷(lei)击(ji)发生(sheng)时(shi),雷(lei)云上(shang)所带的(de)(de)(de)电(dian)(dian)(dian)荷(he),通过(guo)闪击(ji)与地(di)面(mian)的(de)(de)(de)异(yi)种(zhong)电(dian)(dian)(dian)荷(he)迅(xun)速中和,而(er)有些局(ju)部(bu)如架(jia)空导线(xian)(xian)上(shang)的(de)(de)(de)感(gan)(gan)应(ying)(ying)(ying)(ying)电(dian)(dian)(dian)流,由于(yu)和大地(di)间(jian)电(dian)(dian)(dian)阻比较大,不(bu)能(neng)在(zai)同样短(duan)的(de)(de)(de)时(shi)间(jian)内(nei)消失(shi),这(zhei)就形成了(le)局(ju)部(bu)的(de)(de)(de)感(gan)(gan)应(ying)(ying)(ying)(ying)高(gao)电(dian)(dian)(dian)压(ya)。这(zhei)种(zhong)感(gan)(gan)应(ying)(ying)(ying)(ying)高(gao)电(dian)(dian)(dian)压(ya)在(zai)高(gao)压(ya)架(jia)空线(xian)(xian)路上(shang)可(ke)(ke)达(da)300-400KV,在(zai)低压(ya)架(jia)空线(xian)(xian)路上(shang)可(ke)(ke)达(da)100KA,在(zai)电(dian)(dian)(dian)信线(xian)(xian)路上(shang)可(ke)(ke)达(da)4-60KV,在(zai)有线(xian)(xian)电(dian)(dian)(dian)视线(xian)(xian)路上(shang)可(ke)(ke)达(da)20-40KV,在(zai)建(jian)筑物(wu)上(shang)也可(ke)(ke)以产生(sheng)相(xiang)当高(gao)的(de)(de)(de)有危险的(de)(de)(de)电(dian)(dian)(dian)压(ya)。这(zhei)种(zhong)由于(yu)静电(dian)(dian)(dian)感(gan)(gan)应(ying)(ying)(ying)(ying)感(gan)(gan)应(ying)(ying)(ying)(ying)产生(sheng)的(de)(de)(de)过(guo)电(dian)(dian)(dian)压(ya),不(bu)仅对接地(di)不(bu)良的(de)(de)(de)电(dian)(dian)(dian)气系统有破坏作(zuo)用,而(er)且对于(yu)对于(yu)金属构架(jia)与接地(di)不(bu)良的(de)(de)(de)金属器(qi)件之(zhi)间(jian)容易发生(sheng)火(huo)花,对存放易燃易爆(bao)(bao)物(wu)品的(de)(de)(de)地(di)方或生(sheng)产场所,引(yin)起火(huo)灾或爆(bao)(bao)炸事故。

   (2)电磁(ci)感(gan)应(ying):由于雷电流有极大(da)峰(feng)值和陡度,在它周围的(de)(de)(de)空间有强大(da)的(de)(de)(de)变化的(de)(de)(de)电磁(ci)场,处在这(zhei)电磁(ci)场中的(de)(de)(de)导体会感(gan)应(ying)出较大(da)的(de)(de)(de)电动势。这(zhei)种电磁(ci)感(gan)应(ying)也会引起易燃物的(de)(de)(de)火灾和易爆物的(de)(de)(de)爆炸。

    5、雷电(dian)反击和引入高(gao)电(dian)位

    (1)、雷(lei)电(dian)反(fan)击,直击雷(lei)击中的金(jin)属(shu)(shu)体(ti)(包括接(jie)闪器、接(jie)地(di)引线和接(jie)地(di)体(ti))时,该金(jin)属(shu)(shu)体(ti)在(zai)接(jie)闪瞬间与(yu)大地(di)存在(zai)很高(gao)的电(dian)压(ya),这电(dian)压(ya)对与(yu)大地(di)连接(jie)的其他(ta)金(jin)属(shu)(shu)物(wu)品会发生闪击。

    (2)、雷(lei)电(dian)引入高电(dian)位,当直击(ji)雷(lei)或感应雷(lei)从(cong)输电(dian)线、通信电(dian)缆、无线电(dian)天线等(deng)金属的(de)引入线引入建筑物内时,会(hui)发(fa)生闪击(ji)而造成雷(lei)击(ji)事故。

三(san)、雷(lei)电入侵途(tu)径

    1、雷(lei)电闪击到建(jian)筑物时,雷(lei)电能量通过电位(wei)反击、各(ge)种耦合(he)机制(zhi)(电流耦合(he)、电感耦合(he)、电容(rong)耦合(he))及电磁(ci)脉冲辐射等方式沿(yan)供电线(xian)路、通信线(xian)路、网络线(xian)路和金属管(guan)线(xian)进入设备,造成设备的损(sun)坏。以(yi)雷(lei)击中心1.5~3 km为半径(jing)的范围内(nei),雷(lei)电电磁(ci)脉冲辐射冲辐射沿(yan)各(ge)种线(xian)路进入设备。

    2、在高压输电(dian)线路上发生雷击时,线路上产生的过电(dian)压也会沿线路传送,直到变压器的低侧,造成设备的损坏。

    3、雷云与雷云之间放电(dian),同样会产生雷电(dian)浪涌,通过各种金属(shu)导体的线路进入设备。

    4、云层带(dai)电,使(shi)地面上某一(yi)建筑物表面或(huo)长导线感(gan)应带(dai)异(yi)号电荷,产生电涌(yong)进入设(she)备。

四、雷电防护分区

    依据GB50343《建筑物电子信(xin)息系统防(fang)(fang)雷技术规范》,将建筑物按需(xu)要(yao)防(fang)(fang)护(hu)的(de)空间由表(biao)及里划分为不同的(de)雷电防(fang)(fang)护(hu)区(qu):直击雷非防(fang)(fang)护(hu)区(qu)(LPZOA)、直击雷防(fang)(fang)护(hu)区(qu)(LPZOB)、**防(fang)(fang)护(hu)区(qu)(LPZ1)、第二防(fang)(fang)护(hu)区(qu)(LPZ2)、后续(xu)防(fang)(fang)护(hu)区(qu)(LPZn)。如图5-2。

    雷电防护分区实(shi)际(ji)意义:

    1、可以(yi)计算出各LPZ内空间雷埚电磁脉冲的(de)强度,以(yi)确认是否(fou)需采取进一步的(de)屏蔽(bi)措施。

    2、可以确(que)定等电位连(lian)接的位置(一般(ban)是(shi)各LPZ区交界(jie)处)。

    3、可以确(que)定(ding)在(zai)不同(tong)LPZ交界处选(xuan)用(yong)电涌(yong)保护器的(de)具体指标。

    4、可以选定敏感电子设备(bei)的(de)**放置(zhi)位置(zhi)。

    5、可(ke)以(yi)确定在(zai)不同(tong)LPZ交界处等电位连(lian)接导体的最(zui)小(xiao)芯(xin)线截面(mian)。


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