Requirements for Increased Safety Type Explosion-Proof Structure

According to the principles of increased safety in explosion-proof design, there are specific requirements for the casing protection, electrical insulation, wire connections, electrical clearances, creepage distances, maximum temperatures, and windings in electrical equipment.

1. Casing Protection:

Generally, the protection level of the casing in increased safety electrical equipment is as follows:
Minimum IP54 protection is required when the casing contains exposed live parts.

Minimum IP44 protection is required when the casing contains insulated live parts.

When inherently safe circuits or systems are inside the increased safety electrical equipment, these circuits should be segregated from non-inherently safe circuits. Circuits without an inherent safety level should be housed in a casing with a protection level of at least IP30, with warning signs stating “Do not open when live!”

2. Electrical Insulation:

Under rated operating conditions and permissible overload conditions, the maximum operating temperature of increased safety electrical equipment should not adversely affect the mechanical and electrical properties of the insulation material. Therefore, the heat and moisture resistance of the insulation material should be at least 20K higher than the maximum operating temperature of the equipment, with a minimum of 80°C.

3. Wire Connections:

For increased safety electrical equipment, wire connections can be divided into external electrical connections (where external cables enter the casing) and internal electrical connections (connections between components within the casing). Both external and internal connections should use copper core cables or wires.

For external connections, the external cable should enter the casing through a cable entry device.

For internal connections, all connecting wires should be arranged to avoid high-temperature and moving parts. Long wires should be properly fixed in place. Internal connecting wires should not have intermediate joints.

Additionally, wire-to-terminal or bolt-to-nut connections must be safe and reliable.

In summary, contact resistance at wire contact points should be minimized to avoid becoming a “danger temperature” ignition source; loose contacts can cause electric sparks due to poor contact.

4. Electrical Clearance and Creepage Distance:

Electrical clearance (the shortest distance through air) and creepage distance (the shortest path along the surface of an insulating material) are crucial indicators of the electrical performance of increased safety electrical equipment. If necessary, ribs or grooves can be added to insulating components to increase electrical clearance and creepage distance: ribs with a height of 2.5mm and thickness of 1mm; grooves with a depth of 2.5mm and width of 2.5mm.

5. Limiting Temperature:

The limiting temperature refers to the highest allowable temperature of explosion-proof electrical equipment. The maximum heating temperature of the parts of increased safety electrical equipment that may come into contact with explosive gas mixtures is a critical factor in determining their explosion-proof performance. The maximum heating temperature should not exceed the limiting temperature for the safe increased safety electrical equipment (temperature class of the explosion-proof equipment), as it may ignite the corresponding explosive gas mixture.

When designing increased safety explosion-proof electrical equipment, in addition to considering the electrical and thermal performance of electrical components, appropriate temperature protection devices should be incorporated to prevent certain components from exceeding the limiting temperature.

Windings:

Increased safety electrical equipment such as motors, transformers, solenoids, and ballasts for fluorescent lamps all contain windings. Coils should have higher insulation requirements than regular coils (see relevant national standards) and should be equipped with temperature protection devices to prevent the coils from exceeding the limiting temperature under normal operation or specified fault conditions. The temperature protector can be installed either inside or outside the equipment and should have the corresponding explosion-proof type.