“Ex d IIB + H2”保护方法：IIC的有效替代

本文主要介绍关于Ex d IIB + H2的相关信息。

“ Ex d”保护方法采用防爆接线盒，防爆接线盒是一种特殊类型的接线盒，其构造是为了容纳电气设备并承受外壳本身内部发生的任何爆炸所引起的压力。

这种保护方法用于存在潜在爆炸性气体的环境中。

“ Ex d”保护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，因为它基于非常简单（因此不太可能出错）的技术。该原理假设无法阻止气体渗透到任何地方。没有垫圈将无法防止气体进入接线盒！

因此，如果爆炸性气氛渗透到接线盒中而产生触发，例如由两个电触点之间的火花引起的触发，则发生爆炸，但爆炸仍被限制在外壳内。

为了确保这一原理，接线盒必须具有一定的机械强度，能够承受爆炸引起的超压，从而使燃烧的气体得以逸出。

这是火焰路径的电荷，它是接线盒的两个部分（例如主体和盖子）之间的接口。火焰路径使燃烧的气体从外壳中冷却下来，从而不再能够触发外部大气。

因为这个原因，火焰路径必须足够长，并且间隙必须足够窄，以保证烟气的冷却。

根据气体和接线盒的体积，应遵守EN 60079-0和EN 60079-1标准中规定的精确规则。

"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.

监管原则

EN 60079-0标准建立了可在具有爆炸危险的环境中使用的设备的一般规则，将电气设备分为三组：

• Group I

• Group II

• Group III

Group I包括可用于可能存在沼气的矿井中使用的设备。III类的设备可用于存在粉尘的潜在爆炸性环境的区域，而II类的设备可用于由于存在表面气体而存在爆炸性环境的地方，即不同于沼气的地方。

Group II类电气设备根据爆炸性气体的存在而针对其进行了划分。

在这种情况下，划分为三组：

•IIA，该类的典型气体是丙烷；

•IIB，典型的气体是乙烯；

•IIC，典型的气体是氢气和乙炔。

此划分基于最大的实验安全间隙，即MESG：由爆炸引起的火焰（可能在外壳内部发生事故时发生）必须冷却，如上面所述，通过火焰路径根据气体类型的不同，其构造方法和长度也不同。

对于危险性较小的气体，如IIA和IIB组的气体，可以使用扁平，角形，圆柱形火焰路径等。而对于以IIC组代表的最危险的气体，火焰路径只能是圆柱形的或螺纹连接，仅用于极小体积的法兰连接。

在不会导致这些选择的技术设计原因的前提下，可以概括地说，IIA和IIB组的火焰路径是平坦的，而IIC组的火焰路径是圆柱形或螺纹的。

IIA和IIB之间的构造方法相同，差异仅体现在火焰路径长度上，IIB组差异更大。

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.

构造差异和应用

大多数“ Ex d”接线盒是为IIB和IIC设计和制造的。IIA和IIB之间的结构差异非常有限，有利于IIA的成本差异不足以证明是双重产品。因此，通常情况下，即使对于IIA，也使用IIB接线盒。对于IIC，对于容积大于0.5升的接线盒，火焰路径不能平坦，而必须是圆柱形的，因此，IIC内部的构造技术必须与IIB接线盒不同。

通常，生产圆柱形火焰路径的需要制造商建造圆形或方形的外壳。通常首选为IIB型的外壳，以便更轻松地实现由通过适当的密封配件连接的并排外壳组成的配电盘。

多年来，技术人员产生的理念：对于IIC区域，必须使用带有圆柱形火焰通道的接线盒，该接线盒通常具有圆形主体和固定螺纹毂，这会使面板的构造更加复杂。

这种看法并不确切。如果阅读EN 60079-1标准，我们会发现，只有爆炸性气体以乙炔为特征时，IIC集团才允许在大于0.5升的容积中使用扁平法兰式火焰通道。相反，它们可以在氢存在下被允许。

因此，近年来，即使在存在氢气的情况下，也开始生产可使用的“ Ex d”防爆外壳以及IIB类的气体。

可以通过检查标记在产品目录上的存在来验证该应用是否合适：

Ex d IIB + H2

这意味着接线盒可以在含有爆炸性气体和氢气的环境中使用。因此，乙炔被排除在外，但我们必须考虑到存在氢的环境比发生乙炔的环境更为频繁。

采用防护等级Ex d IIB + H2的方法，接线盒采用带法兰的火焰路径制造，并具有这些接线盒的所有典型构造优势：矩形或方形，可以轻松组装以制造电气面板。

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

除了易于组装矩形外壳以制造电气面板之外，还有一个不可忽略的因素也体现在成本上，通常，IIB组接线盒的成本要低于IIC组的接线盒。

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.