“Ex d IIB + H2”保護(hù)方法：IIC的有效替代
本文主要介紹關(guān)于Ex d IIB + H2的相關(guān)信息。
“ Ex d”保護(hù)方法采用防爆接線盒，防爆接線盒是一種特殊類型的接線盒，其構(gòu)造是為了容納電氣設(shè)備并承受外殼本身內(nèi)部發(fā)生的任何爆炸所引起的壓力。
這種保護(hù)方法用于存在潛在爆炸性氣體的環(huán)境中。
“ Ex d”保護(hù)方法是最古老的方法，也是最早用于防止爆炸的方法，仍然是最安全的方法之一，因?yàn)樗诜浅：?jiǎn)單（因此不太可能出錯(cuò)）的技術(shù)。該原理假設(shè)無(wú)法阻止氣體滲透到任何地方。沒(méi)有墊圈將無(wú)法防止氣體進(jìn)入接線盒！
因此，如果爆炸性氣氛滲透到接線盒中而產(chǎn)生觸發(fā)，例如由兩個(gè)電觸點(diǎn)之間的火花引起的觸發(fā)，則發(fā)生爆炸，但爆炸仍被限制在外殼內(nèi)。
為了確保這一原理，接線盒必須具有一定的機(jī)械強(qiáng)度，能夠承受爆炸引起的超壓，從而使燃燒的氣體得以逸出。
這是火焰路徑的電荷，它是接線盒的兩個(gè)部分（例如主體和蓋子）之間的接口?；鹧媛窂绞谷紵臍怏w從外殼中冷卻下來(lái)，從而不再能夠觸發(fā)外部大氣。
因?yàn)檫@個(gè)原因，火焰路徑必須足夠長(zhǎng)，并且間隙必須足夠窄，以保證煙氣的冷卻。
根據(jù)氣體和接線盒的體積，應(yīng)遵守EN 60079-0和EN 60079-1標(biāo)準(zhǔn)中規(guī)定的精確規(guī)則。
"Ex d" method of protection uses explosion-proof junction boxes, a particular types of box constructed in order to accommodate electrical equipment and to withstand the pressure caused by any explosion occurred inside the enclosure itself.
This protection method is used in environments with a potentially explosive atmosphere for the presence of gas.
The "Ex d" method of protection is the oldest and the first used to prevent explosions, still one of the safest because based on a very simple and, therefore, unlikely fallible technology. The principle assumes that it’s impossible to prevent a gas to penetrate everywhere. No gasket will never be able to prevent the entry of a gas in a junction box!
Therefore, if an explosive atmosphere penetrates in a junction box producing a trigger, for example caused by a spark between two electrical contacts, the explosion occurs, but it remains confined within the enclosure.
To ensure this principle, the junction box must be constructed with a mechanical strength able to contain the over pressure caused by the explosion, allowing the escape of the burned gases.
This is the charge of the flame-path which is the interface between two parts of a junction box, such as body and lid. The flame-path allows the burned gases to exit from the enclosure cooling down, so that they are no longer able to trigger the external atmosphere.
For this reason, the flame-path must be sufficiently long and with a gap enough narrow to guarantee the cooling of the flue gases.
There are precise rules to be respected, depending on the gas and on the volume of the junction boxes, prescribed in EN 60079-0 and EN 60079-1 standards.
監(jiān)管原則
EN 60079-0標(biāo)準(zhǔn)建立了可在具有爆炸危險(xiǎn)的環(huán)境中使用的設(shè)備的一般規(guī)則，將電氣設(shè)備分為三組：
? Group I
? Group II
? Group III
Group I包括可用于可能存在沼氣的礦井中使用的設(shè)備。III類的設(shè)備可用于存在粉塵的潛在爆炸性環(huán)境的區(qū)域，而II類的設(shè)備可用于由于存在表面氣體而存在爆炸性環(huán)境的地方，即不同于沼氣的地方。
Group II類電氣設(shè)備根據(jù)爆炸性氣體的存在而針對(duì)其進(jìn)行了劃分。
在這種情況下，劃分為三組：
?IIA，該類的典型氣體是丙烷；
?IIB，典型的氣體是乙烯；
?IIC，典型的氣體是氫氣和乙炔。
此劃分基于最大的實(shí)驗(yàn)安全間隙，即MESG：由爆炸引起的火焰（可能在外殼內(nèi)部發(fā)生事故時(shí)發(fā)生）必須冷卻，如上面所述，通過(guò)火焰路徑根據(jù)氣體類型的不同，其構(gòu)造方法和長(zhǎng)度也不同。
對(duì)于危險(xiǎn)性較小的氣體，如IIA和IIB組的氣體，可以使用扁平，角形，圓柱形火焰路徑等。而對(duì)于以IIC組代表的最危險(xiǎn)的氣體，火焰路徑只能是圓柱形的或螺紋連接，僅用于極小體積的法蘭連接。
在不會(huì)導(dǎo)致這些選擇的技術(shù)設(shè)計(jì)原因的前提下，可以概括地說(shuō)，IIA和IIB組的火焰路徑是平坦的，而IIC組的火焰路徑是圓柱形或螺紋的。
IIA和IIB之間的構(gòu)造方法相同，差異僅體現(xiàn)在火焰路徑長(zhǎng)度上，IIB組差異更大。
Regulatory principles
The EN 60079-0 standard, which establishes the general rules for equipment that can be used in environments with a potentially explosive atmosphere, divides the electrical equipment into three groups:
? Group I
? Group II
? Group III.
The Group I includes equipment that can be used in mines where firedamp gas may be present. The Group III has equipment that can be used in areas with potentially explosive atmosphere for the presence of dusts, while those belonging to the Group II can be used in places with the presence of an explosive atmosphere due to the presence of surface gases, i.e. different from firedamp.
The electrical equipment of Group II are divided in accordance to the explosive atmosphere for the presence of those gases to which they are intended.
The division is, also in this case, into three groups:
? IIA, a typical gas of this Group is the Propane;
? IIB, a typical gas is the Ethylene;
? IIC, typical gases are Hydrogen and Acetylene.
This division is based on the maximum experimental safety gap, called MESG: the flame caused by the explosion, which may occur in the event of an accident inside the enclosure, must be cooled down passing, as wrote above, through the flame-path which has different construction methods and length depending on the type of gas.
For less dangerous gases, as those of IIA and IIB Groups, you can use the flat, corner, cylindrical flame-path etc.., while for the most dangerous gas, represented by the Group IIC, the flame-path can only be cylindrical or threaded, flanged only for very small volumes.
Without going into technical design reasons that have led to these choices, can generalize, without getting wrong, stating that the flame-path for Groups IIA and IIB is flat, while for the IIC group it’s cylindrical or threaded.
The constructive methodology between the IIA and IIB is the same, the difference is represented only by the flame-path length, greater for the IIB Group.
構(gòu)造差異和應(yīng)用
大多數(shù)“ Ex d”接線盒是為IIB和IIC設(shè)計(jì)和制造的。IIA和IIB之間的結(jié)構(gòu)差異非常有限，有利于IIA的成本差異不足以證明是雙重產(chǎn)品。因此，通常情況下，即使對(duì)于IIA，也使用IIB接線盒。對(duì)于IIC，對(duì)于容積大于0.5升的接線盒，火焰路徑不能平坦，而必須是圓柱形的，因此，IIC內(nèi)部的構(gòu)造技術(shù)必須與IIB接線盒不同。
通常，生產(chǎn)圓柱形火焰路徑的需要制造商建造圓形或方形的外殼。通常首選為IIB型的外殼，以便更輕松地實(shí)現(xiàn)由通過(guò)適當(dāng)?shù)拿芊馀浼B接的并排外殼組成的配電盤。
多年來(lái)，技術(shù)人員產(chǎn)生的理念：對(duì)于IIC區(qū)域，必須使用帶有圓柱形火焰通道的接線盒，該接線盒通常具有圓形主體和固定螺紋轂，這會(huì)使面板的構(gòu)造更加復(fù)雜。
這種看法并不確切。如果閱讀EN 60079-1標(biāo)準(zhǔn)，我們會(huì)發(fā)現(xiàn)，只有爆炸性氣體以乙炔為特征時(shí)，IIC集團(tuán)才允許在大于0.5升的容積中使用扁平法蘭式火焰通道。相反，它們可以在氫存在下被允許。
因此，近年來(lái)，即使在存在氫氣的情況下，也開(kāi)始生產(chǎn)可使用的“ Ex d”防爆外殼以及IIB類的氣體。
可以通過(guò)檢查標(biāo)記在產(chǎn)品目錄上的存在來(lái)驗(yàn)證該應(yīng)用是否合適：
Ex d IIB + H2
這意味著接線盒可以在含有爆炸性氣體和氫氣的環(huán)境中使用。因此，乙炔被排除在外，但我們必須考慮到存在氫的環(huán)境比發(fā)生乙炔的環(huán)境更為頻繁。
采用防護(hù)等級(jí)Ex d IIB + H2的方法，接線盒采用帶法蘭的火焰路徑制造，并具有這些接線盒的所有典型構(gòu)造優(yōu)勢(shì)：矩形或方形，可以輕松組裝以制造電氣面板。
Construction differences and application
The majority of "Ex d" junction boxes is designed and built for IIB and IIC Groups. The structural differences between the IIA and IIB are,very limited and the cost difference, in favor of the IIA, is not enough to justify a double production. Therefore, normally, are used IIB junction boxes even for the IIA. For the IIC Group, the flame-path cannot be flat for junction boxes with volumes greater than 0.5 liters, but must be cylindrical and, therefore, the construction technology of the IIC enclosures must necessarily be different than IIB junction boxes.
Very often, the need to manufacture a cylindrical flame-path obliges the manufacturer to build round or square-shape enclosures. IIB enclosures, normally rectangular-shape, are preferred for the easier realization of switchboards composed of side by side enclosure connected through appropriate sealing fittings.
Over the years, the technicians settled the concept that, for IIC areas, have to be necessarily used junction boxes with cylindrical flame-path, which usually feature a round-shape body and fixed threaded hubs that make more complicated the construction of panel boards.
This bias is not exact. If we read the EN 60079-1standard, we find that the flat flanged flame-paths are not permitted in the IIC Group for volumes larger than 0.5 liters only if the explosive atmosphere is characterized by acetylene. Instead, they are allowed in the presence of hydrogen.
In recent years, therefore, started the production of “Ex d” explosion-proof enclosures which are usable, as well as with the gases of IIB Group, even in the presence of hydrogen.
It’s possible to verify whether this application is suitable by checking the presence on the product catalog of the marking:
Ex d IIB + H2
This means that the junction box can be used in an environment containing explosive atmosphere with hydrogen. Acetylene is, therefore, excluded, but we must consider that the environments with the presence of hydrogen are much more frequent than those with acetylene.
With the method of protection Ex d IIB + H2, the junction boxes are manufactured with flanged flame-path and have all the constructive advantages typical of these boxes: as rectangular or square-shaped, they can be easily assembled to make electrical panels.
成本
除了易于組裝矩形外殼以制造電氣面板之外，還有一個(gè)不可忽略的因素也體現(xiàn)在成本上，通常，IIB組接線盒的成本要低于IIC組的接線盒。
The cost
A factor not negligible, in addition to the ease of assembling of rectangular-shaped enclosures to make electrical panels, is also represented by the cost, which is normally lower for Group IIB junction boxes than those for Group IIC.
