Shenhai Explosion-Proof
Flameproof Type:
Principle of Explosion Protection:
The principle of flameproof protection involves using an explosion-proof casing that withstands the explosive force within, preventing the internal mixture from spreading to the surrounding area. All flameproof gaps are less than the maximum experimental safe gap for the combustible gas in question (under standard test conditions, the largest gap between two parts of a joint, which will not ignite an external explosive mixture when the easiest to ignite concentration of an explosive mixture inside the casing is ignited). If combustible gas enters the casing and ignites, causing an explosion, the explosive flames are contained within the casing, unable to ignite external explosive mixtures, thus ensuring the safety of the surrounding environment.
Advantages:
Flameproof enclosures are widely applied with a relatively simple structural design.
Disadvantages:
They are bulky and have specific requirements for cables, joints, conduits, linings, and sleeves (the inner diameter of the rubber sealing ring within the sleeve should match the sleeve’s outer diameter and be secured with a compression nut; if steel pipe sleeves are used, they should be sealed with packing as prescribed; if a sleeve without a cable is used, the inlet must be sealed according to standard requirements). It is not permitted to open the casing while energized in hazardous environments; opening the casing requires specialized tools, and incorrect installation and maintenance can lead to dangerous situations. Flameproof enclosures are not permitted in Zone 0 and are typically used for motors, lighting, etc.
Intrinsically Safe Type:
Principle of Explosion Protection:
Intrinsically safe, or “Intrinsic Safety,” refers to a principle of explosion protection where the energy of electrical sparks or thermal effects produced within a device or its exposed connecting wires is limited to a level that cannot ignite. This means that under normal operation or specified fault conditions, no designated explosive mixture can be ignited. Main protective measures include limiting the circuit’s voltage and current and the circuit’s capacitance and inductance, divided into Type ia (allowing two fault points) and Type ib (allowing one fault point).
Advantages:
Devices do not require special cables, making it safer for operators to handle maintenance and repairs, and covers may be opened while powered.
Disadvantages:
It is not suitable for high-power devices and is generally used for low-power devices in measurement, control, and communication. ‘Ib’ type can operate in Zone 0; ‘Ib’ type can operate in Zone 1.
Positive Pressure Types:
Principle of Explosion Protection:
The principle of positive pressure types explosion protection involves introducing fresh air or inert gas at a certain pressure into the enclosure, preventing combustible gases from entering and, thus, preventing ignition sources from contacting explosive gases, thereby preventing explosions. Key measures for pressurized electrical equipment include maintaining a protective gas (fresh air or inert gas) pressure within the casing greater than 50 Pascals. Requirements for pressurized electrical equipment include: the casing, pipelines, and their connections must withstand 1.5 times the maximum positive pressure with all exhaust ports closed under normal working conditions as specified by the manufacturer, with a minimum pressure of 200Pa. The protective air intake must be located in a non-hazardous area, free of corrosive media; exhaust must be located in a non-hazardous area, or spark and particle isolation baffles must be considered; devices that monitor air pressure and flow must be set according to product nameplate or manual specifications.
Advantages:
Can be used when other methods are not applicable.
Disadvantages:
Installation and maintenance are complex and costly; if instruments encounter flammable mixtures, other protective measures must be taken; no energized cover work is permitted. Typically used for large motors, transformers, and high-voltage switches. Permitted usage range: Instruments with automatic power-on functions can be used in Zone 1; instruments with operating acoustic-optic alarms can be used in Zone 2.
Currently, our company’s explosion-proof products mainly include flameproof, intrinsically safe, and pressurized types. Regardless of the method, the fundamental principle is to prevent electrical equipment from becoming an ignition source. The most basic method to prevent explosions is to ensure that the three elements of combustion—fuel, oxidizer, and ignition source—do not coexist in time and space. After considering various working conditions, the most suitable type of explosion-proof electrical product should be selected, taking into account cost and ease of maintenance, to minimize the risk of on-site hazards.