Besides affecting the health of workers, the damp environment of underground spaces can also cause corrosion and damage to electrical equipment. Dampness is an inherent characteristic of underground spaces, and the hot and humid environment of underground engineering projects significantly impacts the reliability of electrical equipment. As modern underground engineering projects place increasingly higher demands on their internal environment, especially in the information age, computer control and intelligent management technologies have been introduced into the control and management of internal equipment. The technological content of internal equipment is becoming increasingly sophisticated, leading to higher requirements for the internal environment of the equipment and systems themselves. The quality of the internal environment of underground engineering projects has become a fundamental guarantee for the reliable operation of internal equipment and systems.
For electrical equipment used in high-humidity environments, both domestically and internationally, the current approach is to treat the components themselves for moisture protection to improve their protective performance. However, using moisture-resistant components is costly, so except for special applications such as shipbuilding, almost all applications use ordinary switching devices. For distribution boxes where equipment is concentrated, overall moisture protection is implemented, such as using resistance wire heating to dry the boxes and reduce the relative humidity inside. However, this method of moisture protection leads to a resurgence of relative humidity inside the box after the equipment stops operating, potentially causing condensation and accelerating corrosion of the electrical equipment. Therefore, researching the moisture protection of electrical distribution boxes in underground engineering is of significant importance and practical value.
I. Sealing Technology of Electrical Distribution Boxes
Electrical distribution boxes are typically sealed and protected using gaskets or sealing strips. When the box door is closed and applies pressure to the box, the gasket or sealing strip is compressed and deformed under the force, which compensates for unevenness in the box components and the surface of the gasket or sealing strip, thus achieving a sealing and protective effect.
Research on moisture-proof technology for underground electrical distribution boxes
II. Selection and Placement Techniques of Desiccant Inside Electrical Distribution Boxes
Sealing the distribution box prevents humid air from seeping inside, but opening and closing the door allows this air to enter. Without proper ventilation, this trapped moisture will damage the electrical equipment inside, causing harm. Therefore, while sealing the distribution box, it's essential to consider drying and absorbing moisture. A common method is to place a desiccant inside the box. The selection of a desiccant is as follows:
Based on the form of reaction, desiccants can be classified into physical adsorption type and chemical adsorption type.
Physical adsorption desiccants utilize the porosity of substances to absorb water vapor. Even when saturated with absorbed moisture, they do not deliquesce or change in form, and are recyclable. Examples include silica gel desiccants and clay desiccants.
Chemical adsorption desiccants absorb moisture through chemical reactions or deliquescence. They generate heat during rapid absorption and are not reusable, such as lime desiccants and salt-based desiccants.
III. Pressure differential protection design for sealed electrical distribution boxes during intermittent operation
For electrical distribution boxes in underground engineering projects that operate intermittently, a significant pressure difference arises between the inside and outside of the box before and after each operation due to the thermal expansion and contraction of the air inside. If left unaddressed, this can affect the overall protective performance of the box and accelerate damage to the seals. To avoid this, a device (such as a transformer breather) can be installed inside the distribution box to prevent direct airflow between the inside and outside (e.g., a transformer breather) to eliminate the pressure difference caused by the thermal expansion and contraction of the air.
Most electrical equipment used in existing underground engineering projects operating in high-humidity environments employs conventional, surface-mounted equipment, with very few specialized moisture-proof electrical products. Therefore, researching sealing and moisture-proofing technologies for electrical distribution boxes, and developing corresponding products, has become an urgent priority, particularly for the development and utilization of underground spaces.
