The reason for the temperature rise of the switchgear
Switchgear is well-known as important electrical equipment. There are mainly HV switchgear, MV switchgear, and LV switchgear. The switchgear may heat up after being energized.
What are the reasons? Here are the reasons why the switchgear heats up:
(1) The expansion effects of different metals in switchgear are different. The metal expansion coefficient of steel bolts is much smaller than that of copper and aluminum busbars. Especially for bolt-type equipment joints, the expansion and contraction of aluminum or copper and iron will change with the load current and temperature during operation. Creep occurs when there is a difference, that is, the metal is slowly plastically deformed under the effect of stress. The creep process also has a great relationship with the temperature of the joint. The practice has proved that when the operating temperature of the joint exceeds 80°C, the joint metal will expand due to overheating, causing the position of the contact surface to stagger, forming tiny voids and oxidizing. When the load current decreases and the temperature returns to the original contact position, due to the coverage of the oxide film on the contact surface, it is impossible to be the direct contact between the metals during the original installation. The increased contact resistance of each cycle of temperature change will increase the heat of the next cycle, and the increased temperature will further deteriorate the working condition of the joint, thus forming a vicious cycle.
(2) The data measured in the type test is usually completed in the laboratory, the duration is not long, usually not more than 8h, does not have the cumulative effect of temperature rise, and can not be equal to the long-term operation and continuous heating equipment. Switchgear
(3) Improper pressure on the tightening bolts at the connection site. Some installation or maintenance personnel believe that the tighter the connection bolts, the better. In particular, the aluminum bus bar has a small elastic coefficient. When the pressure of the nut reaches a certain critical pressure value, if the strength of the material is poor, and the improper pressure is increased, the contact surface will be deformed and raised, but the contact area will be reduced. The contact resistance increases, which affects the conductor contact effect. The conductivity of the selected conductor material does not meet the requirements, and most of them belong to the insufficient purity of the conductor raw materials. Switchgear
(4) Other factors on the site, such as possible improper installation and maintenance process, such as busbars in the processing, connection, installation process, the busbar contact surface treatment are not in place, uneven, not smooth, not coated with special power grease, etc., resulting in effective The contact area decreases and the contact resistance increases and heat is generated.
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