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Introduction to Explosion proof Types in Explosion proof Design

SINO Testing Services

| 2019-12-12|Return

1、 Explosion proof electrical equipment "d"

Explosion proof enclosure: capable of withstanding the explosive pressure of internal explosive gas mixtures and preventing internal explosions from spreading to the surrounding explosive mixtures of your equipment enclosure. Create a sturdy casing for electrical equipment, with gaps between all seams less than the maximum test safety gap for the corresponding combustible gas. If a combustible gas enters the casing and is ignited by a spark, causing an explosion, the explosion flame is confined within the casing and cannot ignite explosive mixtures in the environment outside the casing, thus ensuring the safety of the environment.
The explosion-proof shell must meet two basic conditions:

1. The shell has sufficient mechanical strength to withstand internal explosive pressure without damage, and does not produce permanent deformation that affects explosion-proof performance

2. All seams and gaps on the shell wall that are open to the outside world are less than the corresponding maximum test safety gap


 Main explosion-proof measures:

1. Material requirements for explosion-proof shells

2. Requirements for gap length, width, and surface smoothness of explosion-proof joint surfaces

3. Requirements for fasteners and threaded holes

4. Requirements for transparent parts

5. Requirements for adhesives and sealing agents

6. Grounding

7. Cable and conduit entry devices

8. Chain or warning signs, etc
Standard for explosion-proof design reference of explosion-proof electrical products:

GB3836.2-2010 "Non electrical equipment for explosive atmospheres - Part 2: Equipment protected by an explosion-proof enclosure" d ""

2、 Positive pressure electrical equipment "p"

Positive pressure casing: Fresh air or inert gas at a certain pressure is introduced into the casing of the equipment, preventing the surrounding combustible gases from entering the interior of the casing, thereby preventing the ignition source from coming into contact with explosive gases and achieving the purpose of explosion prevention.
Key explosion-proof measures for positive pressure electrical equipment:

1. The pressure of the protective gas (fresh air or inert gas) inside the equipment casing is at least 50Pa higher than the ambient pressure

2. Before powering on electrical equipment, the equipment casing should be flushed with protective gas (usually 5 times the net volume of the casing should be flushed with protective gas)

Therefore, the equipment needs to be equipped with blowers, pipelines, and air pressure relays, which are generally used for large electric motors and control switch equipment
Standard for explosion-proof design reference of positive pressure electrical products:

GB-T3836.5-2017 "Non electrical equipment for explosive atmospheres - Part 5: Equipment protected by positive pressure enclosure p"

3、 Oil filled electrical equipment

Oil filled casing: Immerse the equipment completely or partially in the oil inside the casing, so that the equipment cannot ignite explosive gases above the oil level or outside the casing.
Main explosion-proof measures:

1. Immerse live parts at least 25mm below the oil surface

2. Transformer oil that meets the standard GB2536

3. Oil temperature not allowed to exceed 100 ° C

4. Set oil level indicator

5. Insulation and sealing materials should be oil resistant

6. The maximum on/off capacity of the equipment is 75% of the safety value of the ignition test

This explosion-proof type is mainly used for transformers and high-voltage switches
The standard for explosion-proof design reference of oil filled electrical equipment:

GB3836.6-2004 Electrical Equipment for Explosive Gas Atmospheres Part 6: Oil Immersed "o"


4、 Sand filled electrical equipment "q"

Sand filled shell: The shell is filled with sand material, so that under specified usage conditions, the arc, flame, shell wall, and sand surface generated inside the shell cannot ignite the surrounding explosive mixture.

Main explosion-proof measures:

1. The shell is filled with sand material and has a certain safety height

2. The particle size of quartz sand is 0.25-1.6mm, with a moisture content not exceeding 0.1%

3. Electrical clearance

4. Shell protection level

This explosion-proof type is mainly suitable for products such as fuses, capacitors, etc
The standard for explosion-proof design reference of sand filled electrical equipment:

GB3836.7-2004 Electrical Equipment for Explosive Gas Atmospheres Part 7: Sand filled "q"


5、 Sealing type electrical equipment "m"

Pour the parts of the equipment that may generate sparks or high temperatures into the sealing agent (resin), as they cannot ignite the explosive mixture around them
Main explosion-proof measures:

1. Seal electrical components with resin, with the free surface of the sealing agent and the sealing thickness of the sealed component or conductor not less than 3mm

2. There are regulations on the dielectric strength, water absorption, light resistance, heat and cold resistance, as well as surface resistance of the sealing agent

3. Surface temperature limit
The standard for explosion-proof design reference of sealed electrical equipment:

GB3836.9-2014 Electrical Equipment for Explosive Gas Environments Part 9: Equipment Protected by Encapsulation Type "m"


6、 Intrinsically safe electrical equipment i

Under specified experimental conditions, the electrical sparks or thermal effects generated by the normal operation of the equipment circuit or under specified fault conditions cannot ignite the specified explosive mixture. The main explosion-proof measure for intrinsic safety type is to limit the energy in the circuit, so that the generated spark energy is less than the corresponding minimum ignition energy.
Main explosion-proof measures:

1. Voltage and current limitations of circuits

2. Limitations of capacitance and inductance in circuits

3. Isolation of intrinsically safe circuits and non intrinsically safe circuits

4. Requirements for Reliable Components and Components

5. Regulations on safety barriers

6. Fault analysis and testing regulations, etc

Applicable products: weak current equipment for measurement, control, communication, etc
The standard for explosion-proof design reference of intrinsically safe electrical equipment:

GB3836.4-2010 Electrical Equipment for Explosive Gas Atmospheres Part 4: Equipment Protected by Intrinsic Safety Type "i"

 7、 Enhanced safety electrical equipment "e"

On equipment structures that do not generate sparks, arcs, or may ignite explosive mixtures under normal operating conditions, measures should be taken to improve safety to avoid electrical equipment that experiences these phenomena under normal and recognized overload conditions (including motor stalling conditions).
Enhanced safety electrical equipment does not have explosion-proof enclosures and protective media, and it adopts comprehensive safety measures:

1. Restricting the types of devices

2. The electrical clearance and creepage distance are relatively large

3. Good insulation materials

4. Specify the conductor connection method

5. Reduce temperature rise

6. Improve the protection level of the casing

7. Equipped with appropriate protective devices, etc

Applicable products: asynchronous motors, transformers, junction boxes, etc
The standard for explosion-proof design reference of increased safety electrical equipment:

GB3836.3-2010 Electrical Equipment for Explosive Gas Atmospheres Part 3: Increased Safety Electrical Equipment


8、 Spark free electrical equipment "n"

An explosion-proof type of electrical equipment that cannot ignite the surrounding explosive environment during normal operation and under certain conditions specified in this standard (only referring to the fault conditions of the light source of the lamp)

The non spark type originally only referred to electrical equipment that does not generate sparks or arcs during normal operation, such as AC asynchronous motors. Based on this, some safety measures were taken, such as using non spark materials for fan blades, IP44 or IP54 protection level for the casing, and increasing the electrical gap and creepage distance appropriately. Later, this explosion-proof concept expanded to electrical products that generate sparks during normal operation, and measures such as gas sealing, simple ventilation, or energy limitation were taken according to their situation to achieve a certain level of safety,. Due to the expansion of this explosion-proof type, the term "spark free" is no longer very precise and is now often referred to as the "n" type.
NType devices can be divided into two categories:

1. The equipment does not generate sparks or arcs during normal operation, such as asynchronous motors, transformers, lighting fixtures, and junction boxes. Plug in devices, etc

2. Sparks or arcs are generated during normal operation of equipment, such as switches, relays, etc
NStandard for explosion-proof design reference of electrical equipment:

GB3836.8-2014 Electrical Equipment for Explosive Gas Atmospheres Part 8: Type N Electrical Equipment
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