High/medium voltage switchgear is prone to condensation in high humidity environments, and condensation is one of the important factors causing faults in high/medium-voltage switchgear. One is that condensation occurs on the surface of the insulation, which can cause a decrease in the surface resistivity of the insulation. If accompanied by accumulation of dirt, the risk of flashover increases. Secondly, the irregular condensation of dewdrops can cause distortion of the electric field on the surface of insulation components, leading to partial discharge. It may accelerate insulation aging and even cause breakdown. Thirdly, condensation can also cause oxidation and corrosion of metal conductors. Especially in the case of copper aluminum contact, the reaction speed is accelerated. Fourthly, for composite materials, moisture can easily invade the interior of the material, causing a decrease in insulation. All of these issues may cause internal faults in the switchgear.
The current high/medium-voltage switchgear products have excellent sealing performance. The invasion of humid air is generally caused by the cable sealing part. Wet air initially accumulates at the bottom of the cable and circuit breaker compartments, especially in the area around the current transformer, and accumulates and gradually develops upwards over time.
The process of placing the switchgear in a humid environment, where moist air enters and diffuses within the switchgear. The moist gas first enters the cable compartment and gradually spreads upwards. The cable room is most affected by humid air. The current transformer area in the cable room is most prone to condensation. The temperature of most areas on the surface of the current transformer is low, and the area between the three phases is the main area prone to condensation due to weak air flow.
The busbar compartment is less affected by humid air. Firstly, due to its high position, it is difficult for humid air to directly enter the compartment; The second is that the heat generated by the current flowing through the busbar in the busbar compartment can dissipate a portion of wet air.
The generation of condensation inside the switchgear can lead to a decrease in internal insulation performance, and various insulation defects will gradually develop into breakdown, leading to accidents and having a significant impact on the stability of the regional power system. Therefore, solving the condensation problem in the switchgear is crucial for the safe operation of the switchgear and the stability of the power grid.
How to prevent condensation in electrical switchgear/enclosure
1) The busbar temperature inside the switch cabinet rises fastest, and the temperature distribution of three-phase contact box is uneven. The temperature rise of the contact box far away from the bulkhead (up to 308K) is lower than that of the contact box near the bulkhead (up to 318K), mainly because the contact box far away from the bulkhead has a large contact area with the air and is easy to dissipate heat.
2) The moisture absorption of insulation materials is faster than that of metal materials, and the contact box has a higher surface relative humidity due to its local hollow structure, which is not easy to remove moisture, making it easier to form condensation.
3) Adding ventilation devices can effectively reduce the relative humidity on the surface of the contact box; Adding a heating device locally can effectively increase the surface temperature of the contact box, and the combination of the two can greatly reduce the probability of condensation occurring in the contact box.
4) The optimal installation location for heating and ventilation devices is on the wall of the switchgear cabinet near both the contact box and the casing, which is better than setting a single heating or ventilation device to reduce condensation on the surface of the contact box.
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