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How to design the retricted breathing lamps (ex-proof “nR”)

CESP Ex Wiki Wednesday, 22 June 2022 06:29

Restricted breathing lamps are a kind of "n" type explosion-proof products. They are used in enviroment with potentially explosive gas atmospheres in Zone 2. They are the same as increased safety lamps in terms of use, but their light source types are higher than that of increased safety lamps. The weight is lighter than that of flameproof lamps, but the scope of use is not as wide as that of flameproof lamps. It has the characteristics of light weight and various types of applicable light sources. It is undoubtedly an economical and easy-to-use product for use in places where good lighting is required in zone 2.

According to IEC/EN 60079-15 Type of Protection “ n ”

Electrical installations designed so that ignition is unlikely to occur in normal or abnormal operation. The gas explodes. The main protection methods are classified as follows.

  • nA: Non-Sparking
  • nC: Enclosed-Break (blocked), Hermetically-Sealed (metallicor glass tight seal), Non-Incendive (non-incendive), Sealed device (sealed)
  • nR: Restricted Breathing Enclosure

This new type of product has many novelties in explosion-proof mechanism, characteristics, inspection difficulties and design. Only when designers and users understand these can they be well designed and used.


Part.1 Explosion-proof mechanism for the Restricted breathing lamps

To understand the explosion-proof mechanism of the restrictive breathing lamp, we must first understand where it is used, and understand where to start with this product to consider the explosion-proof structure treatment.

Restricted breathing lamps have certain restrictions on the use of this kind of lamp, which is only allowed to be used in places with potential explosion hazard gas environment 2, that is to say, the place where this lamp is used is relatively less dangerous. In normal operation, there are no explosive hazardous substances in the environment, including gases, vapors and mist, and dangerous explosive gases, vapors or mist will appear only when they fail, and the chance of such failure is very small, and even if there is a failure, the time of failure is very short. It is precisely because of the particularity of the use environment that this kind of lamp only needs to prevent the danger of dangerous substances in rare cases and the duration of dangerous substances is extremely short. Therefore, the shell of this kind of lamp is to limit the amount of gas, vapor and mist entering, rather than preventing gas, vapor and mist from entering.

When the lamp is working normally, the calorific value of the internal light source is relatively high, which will cause the internal gas to expand and form a positive pressure in the light source cavity of the lamp. Due to the formation of positive pressure, the internal gas leaks out. When the lamp is out of use, the inside of the lamp will gradually cool down. At this time, due to the temperature drop in the lamp, the gas volume is reduced. At this time, the air volume in the lamp is smaller than that in the initial state of the lamp, which causes the inside of the lamp. of negative pressure. If the lamp does not take protective measures, and an accident happens at this time, there is a leakage of dangerous substances, then the dangerous substances may enter the lamp. When the lamp is used again, the high temperature inside the lamp may ignite the explosive gas, vapor or mist existing in the lamp, resulting in a dangerous accident. Restricted breathing lamps are based on this characteristic of lamps, and the light source and its related electrical components are put into restricted breathing enclosures. A restricted breathing enclosure is a type of enclosure that restricts the entry of gases, vapors and mists. That is to say, a restricted-breathing luminaire is a luminaire product with a special housing. This product increases the ability of the housing to restrict the ingress of gases, vapors and mists, so hazardous substances do not enter the luminaire for a short period of time. Of course, if the accident lasts for a long time, there will be danger. Therefore, for this kind of lamps, corresponding measures have been taken to further increase the safety. First of all, its use place is limited, and it is only allowed to be used in Zone 2, so that due to the short maintenance time of the accident, the number of accidents is less, and the chance of danger is reduced. At the same time, strict performance inspections have been carried out for the dangerous components in the casing, such as ballasts, lamp sockets, starters, etc., to ensure the safety and reliability of the components. In this way, this explosion-proof lamp is safe.

Before the emergence of restricted breathing lamps, there were two commonly used lamps in the explosion-proof lamps family: explosion-proof lamps and increased safety lamps. Explosion-proof lamps can be used in areas with potentially explosive gas atmospheres in Zone 1. This kind of lamp mainly uses the high strength and explosion-proof property of the product shell to achieve the purpose of explosion-proof, allowing accidents in the surrounding environment and dangerous substances in the lamp. It uses the strength of the lamp shell to prevent the pressure generated by the internal explosion of the lamp from damaging the lamp body and ignites the surrounding environment, and at the same time uses the extremely small gap between the metal joints of the shell to prevent the flame in the lamp from igniting the surrounding flammable substances; Lamps are also a kind of explosion-proof lamps that are widely used. This kind of lamps is designed by adding a series of safety measures, such as increasing the electrical clearance and creepage distance, increasing the protection level of the shell, and using explosion-proof lamps where sparks may occur in the lamps. Measures to deal with, limit the temperature level of lamps, etc. to achieve safety purposes. In my country, most of this type of explosion-proof lamps are used in Zone 2, and only increased safety single-plug fluorescent lamps are allowed to be used in Zone 1.

Through the above description, it is not difficult to find that the restricted-breathing lamps achieve the purpose of explosion-proof by restricting the entry of explosive gas, vapor or mist into the interior of the lamp body through the good sealing of the shell; And high-strength shell to achieve the purpose of explosion-proof; increased safety lamps and lanterns by increasing the safety of the lamp itself to achieve the purpose of explosion-proof lamps. Therefore, these three lamps each have different characteristics.


Part.2 The Feature of the Restricted breathing lamps

Through the description of the explosion-proof principle of restricted-breathing lamps, it is not difficult to find that restricted-breathing lamps mainly improve the reliability of internal components, at the same time increase the protection capability of the shell, and limit their use places. This also determines its different characteristics from other explosion-proof lamps.

First of all, due to the requirements for limiting the protection capability of the internal components and shells of the breathing lamps, the restricted breathing lamps have higher requirements on the selection of internal components: they must be components with reliable performance and firm connections. After the components are selected, the main hazards of this kind of lamps are the limited breathing ability of the shell and the heating problem of the product surface. Therefore, the measurement of the surface temperature in the inspection is to select the surface of the lamp body, which is the same as the explosion-proof product, which also forms a great advantage compared with the increased safety lamps.

The increased safety lamp is to increase the safety of all parts of the lamp, including the temperature limit. Therefore, the temperature measurement of the increased safety lamp is to detect the high surface temperature of each component inside the lamp, so that when the increased safety lamp determines its temperature group The temperature is determined by measuring the high temperature points on the surface of the light source. Therefore, the heat generation of the increased-safety lamps is very high, and their applicable range is narrow. Those flammable gas environments with low ignition temperature are not suitable for the use of increased-safety lamps. It is precisely because the safety-enhancing lamps and lanterns are considering the safety of the internal components of the lamps and lanterns, which have certain restrictions on the use of light sources. In the national standard currently used in my country, only cold-start fluorescent lamps, incandescent lamps and self-ballasted fluorescent lamps are allowed. Light bulbs that ignite for a short time after being broken (verified that the short-term high temperature of the bulb does not cause danger). From the restrictions on the increased safety lamps, it is not difficult to find that the restricted breathing lamps and lanterns use the restricted breathing type casing, so when measuring the surface temperature of the lamp, the temperature of the outer surface of the lamp is measured. In this way, under the condition of good lighting design and good heat dissipation, it is easy to reduce the surface temperature of the lighting and broaden the use range of the lighting. While reducing the surface temperature of the lamps, the types of light sources used by the lamps are also increased. Since the housing is of a restricted breathing type, the interior of the luminaire is relatively safe, so most of the light sources can be used except for those light sources that are dangerous to the luminaire itself. Restricted breathing lamps can use incandescent, mercury, sodium and metal halide lamps as well as fluorescent lamps. In this way, the illuminance of the restricted breathing lamps is greatly increased. Some lamps that need high illumination and high heat generation hanging at the height of the workshop can completely use the restricted breathing lamps, because it is easy to form a zone 2 dangerous place at the height of the workshop.

Secondly, since the restricted breathing type luminaire only needs to have the restricted breathing capacity of the outer casing, it does not need to make the outer casing as thick as the flameproof type lamp, making the lamp very heavy. In this way, in some places that require high illuminance and low degree of danger, restricted breathing lamps can completely replace explosion-proof lamps, because they are lighter than explosion-proof lamps, but they can use the same light source and have the same temperature group. do not. Of course, it cannot be used in Zone 1 hazardous locations, and the scope of use is small, which is incomparable with explosion-proof lamps.

To sum up, the restricted breathing lamp has the characteristics of low external heat generation, wide applicable temperature range, relatively many types of light sources, and relatively light shell.


Part.3 Inspection Difficulties for the Restricted breathing lamps

From the explosion-proof principle and characteristics of restricted breathing lamps, it is not difficult to find the main problems in their inspection.

First of all, the restricted-breathing lamps have high requirements on the performance of the internal components, so the inspection of the internal components of the lamps in the inspection is quite cumbersome. Mainly focus on the inspection of ballasts, lamp sockets and starters. It is mainly the inspection of the ballast and the starter, including the high-voltage pulse test of the ballast and the performance inspection of the starter seat, which not only costs high test costs, but also takes a long time to test.

Secondly, it is a difficult point in the inspection that the enclosure of the restricted breathing luminaire restricts the breathing ability. For longer joints in luminaires, it is difficult to pass the test of the restricted breathing enclosure. Because during the test, it is required to evacuate the shell to -3

kPa, and then rely on the sealing performance of the shell itself so that it does not drop to 1.5kPa within 3min. This test has very strict requirements on sealing and requires very good elasticity of the gasket. In the large number of experiments we have conducted, not a single unit has passed the test at one time, and all of them are continuously improved in the experiment, so as to finalize the final product design.


Part.4 Some techniques that can be used in design of the Restricted breathing lamps

Through the above analysis, several suggestions are put forward for the design of restricted breathing lamps.

First, because of the reduction in the joint surface that restricts the breathing shell. The more surfaces a restricted breathing enclosure has, the more leak points it will have. Conversely, the fewer surfaces a restricted breathing enclosure has, the fewer leak points it will have, so that the chance of passing the restricted breathing enclosure test is better. bigger. Even if there is a leak, it is easy to identify the leak and remedy it.

Second, reduce the length of the joint surface. Due to the high degree of sealing required by the restricted breathing type housing, the longer the distance of a joint surface, the more leakage points. To seal, the sealing distance must be reduced, so that the number of fasteners will increase, which will be difficult to install and disassemble. Add trouble.

Finally, avoid the difficulty in testing. During the inspection, the inspection of some internal components is quite time-consuming; it will also cost a lot of inspection funds, and we can also try to avoid it in the design.


The following takes the restricted breathing lamps as an example to illustrate the design points of the restricted breathing lamps.

  1. Pay attention to the design of the lamp body, which can reduce the high surface temperature of the lamp. The metal part of the lamp should be as large as possible, and the light source should be wrapped in metal as much as possible. Using the principle of parabolic focus, the light should be reflected as much as possible through the lamp body. If there is a reflective umbrella, you can consider the reflective umbrella as close to the lamp body as possible. The body dissipates heat.
  2. In designing the bonding method between the transparent part and the lamp body, the adhesive structure should be considered. Because the joint surface between the transparent part and the lamp body is generally the long joint surface of the lamp, and the problem of rubber aging is easy to occur due to heat generation, it is not suitable to use rubber material for sealing. The surface temperature of the lamp body is a better sealing measure. In this way, this interface can be easily passed during the restricted breathing type enclosure test. However, when using the adhesive, it is necessary to consider the heat-resistant temperature of the adhesive and the damage to the transparent parts of the lamp due to different thermal expansion rates. Usually, the solution to the different thermal expansion rates of adhesives is to add additives of other materials to the sealant, so that the thermal expansion of the glass has a certain space without damage.
  3. Only the light source: wiring socket and lamp socket are installed in the restricted breathing housing, and the starter and ballast are treated with other explosion-proof measures, which can greatly reduce the production cost and inspection cost.
  4. The light source is taken out from the rear of the lamp body or from the side. This reduces the number of luminaire joints and the length of the joints. Lamps generally have three joint surfaces, the transparent part and the lamp cover, the lamp cover and the lamp body, and the lamp body and the junction box cover. Among them, the joint surface between the lamp cover and the lamp body is often used as the place to replace the light source, but this joint surface is relatively large. Due to the need for replacing the light source, the fasteners are not easy to be too many, which forms a contradiction and limits the breathing test. difficult to pass. If the light source is considered to be removed from the rear for replacement, the length of the joint will be greatly shortened, and the joint can be easily sealed with four fasteners. If you are afraid of the performance problem of the lamp caused by the high temperature of the lamp holder caused by taking out the light source from the rear, you can consider dividing the reflector of the lamp into two parts. The large part is fixed and will not be taken out when the light source is taken out; The part is movable and integrated with the lamp holder, when the light source is taken out, it is taken out with it. Its main function is to reflect the light hitting the lamp holder, so that the temperature of the lamp holder is lowered, and at the same time, the sealing material is placed in a low temperature place, which can well prevent the aging of the rubber material.
  5. The choice of sealing material: the sealing material used to seal the restricted breathing enclosure is difficult to choose, and some customers have to repeatedly select a better material when conducting experiments. Of course, high temperature resistance, aging resistance, good material elasticity and good recovery are the main conditions for material selection.
  6. The choice of sealing structure: the sealing structure adopted by most enterprises is usually face sealing. Rubber is sandwiched between the two planes, and this structure has great disadvantages. First of all, it is caused by poor plane processing. Due to poor plane processing, the flatness cannot meet the requirements. In places far from the fasteners, the sealing is often not tight due to uneven force; secondly, the installation hinges do not match. It causes the upper and lower hinges to struggle with each other, and it is not easy to press the gasket at the place where the hinge is installed, which is easy to cause leakage. At present, a better sealing method is to use wire sealing, and make a protrusion for wire sealing on one side of the joint surface, and then press it with a fastener. This kind of sealing effect is better.