Why is the temperature rise of high-voltage switchgear too high?

The actual temperature rise inside the switch cabinet, especially the busbar connection, is usually higher than the data measured in the type test. The main reasons are as follows:

(1) The data measured in the type test is usually completed in the laboratory, and the duration is not long, usually not more than 8 hours. It does not have the cumulative effect of temperature rise, and cannot be equivalent to the equipment that operates for a long time and continuously heats up.

(2) Different metals have different expansion effects. The metal expansion coefficient of steel bolts is much smaller than that of copper and aluminum buses. Especially for bolted equipment joints, with the change of load current and temperature during operation, the expansion and contraction degree of aluminum or copper and iron will be different and creep will occur, that is, the metal will slowly plastic deformation under the effect of stress. The creep process is also greatly related to the temperature at the joint.

It has been proved in practice that when the operating temperature at the joint exceeds 80 ℃, the joint metal will expand due to overheating, which will stagger the positions of the contact surfaces, form tiny voids and oxidize. When the load current decreases and the temperature drops back to the original contact position, due to the coverage of the oxide film on the contact surface, it cannot be the direct contact between metals during the original installation. The increased contact resistance of each temperature change cycle will increase the heat of the next cycle, and the increased temperature will further deteriorate the working condition of the connector, thus forming a vicious cycle.


(3) The fastening bolt pressure at the connection part is improper. Some installation or maintenance personnel think that the tighter the connecting bolts are, the better the conductor connection is. In fact, this is not the case. 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 continued to increase, the deformation and uplift of the contact surface will be caused, instead of reducing the contact area and increasing the contact resistance, which will affect the conductor contact effect.

(4) The conductivity of the selected conductor material does not meet the requirements, most of which are due to the insufficient purity of the conductor raw materials.

(5) Other factors on the site, such as improper installation and maintenance process, such as improper bus contact surface treatment, unevenness, unsmooth, and failure to apply special electric grease during bus processing, connection, and installation, result in reduced effective contact area, increased contact resistance, and heating.

Low voltage switchgear is a low-voltage power distribution assembly that involves the complete assembly of low-voltage switchgear according to a certain wiring scheme. It is used for power and lighting distribution in the power supply system below 1000V. It also has two categories: fixed installation and withdrawable installation.

The EPS-TRT full-automatic temperature rise test bench produced by Wuhan EP Hipot Electric Co., Ltd. is used for the electrical type test of the high and low voltage products produced by the high and low voltage electrical manufacturers before delivery. It provides two functions of large current and temperature detection, which is convenient for users to operate and improve work efficiency. It is used in power plants, power transformation and distribution stations, electrical manufacturers, scientific research, laboratories and other units. The multi-channel temperature recorder adopts the digital synchronous sampling technology, which has the advantages of fast measurement speed, high accuracy, convenient use and beautiful appearance.

Wuhan EP Hipot Electric Co., Ltd. is a high-tech enterprise specializing in the production of high-voltage test and detection equipment. The company has won the unanimous recognition of customers with high-quality products and good reputation. If necessary, you can call us and we will customize the solution for you.

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