Failure and cause analysis caused by the influence of ambient temperature on electrical appliances of low voltage distribution box

① Reactive power compensation capacitors and fuses operating at high temperature will also shorten their service life.

② The electronic products in the distribution box, such as residual current action protector and electronic meter, will seriously affect the service life of the product when operating at high temperature, as well as the stability of protector performance, action reliability and measurement accuracy.

③ All kinds of low-voltage electrical appliances are mostly class a insulation, and their limit allowable temperature rise during long-term operation is 65 ℃. Due to the high temperature in the distribution box and the production of the meter control box, it is difficult for the internal heat of the low-voltage apparatus to dissipate outward during operation, so it is burned out due to insulation aging after a certain period of time; Plastic insulated wires will also be subject to thermal aging and breakdown.

Causes of distribution box failure caused by ambient temperature

The low-voltage electrical apparatus in the distribution box is composed of fuse, AC contactor, residual current action protector, capacitor and electrical measurement digital meter. These low voltage appliances are designed and manufactured according to gb1497 basic standard for low voltage appliances, and their normal working conditions are specified accordingly: the upper limit of air and electricity temperature around the production of Dongguan GCK low voltage cabinet shall not exceed + 40 ℃; The average value of ambient air power temperature for 24h shall not exceed + 35 ℃; The lower limit of ambient air power temperature shall not be lower than - 5 ℃ or - 25 ℃.

In hot and cool days in summer, the low-voltage electrical appliances in the distribution box will also generate heat during operation. In addition, the external ambient temperature is high, and the temperature in the box will reach more than + 60 ℃. At this time, the temperature greatly exceeds the ambient temperature specified in the national standard of these electrical appliances, which will cause the failure of the distribution box. Reducing the temperature of the distribution box and improving the technology of the distribution box are the methods to reduce the failure of the distribution box.

    Earlier, we introduced the precautions for the installation of distribution box and how to fix the distribution box. Today, we will introduce the problems that may be encountered during the installation of distribution box:

① The model selection is not in accordance with the drawing requirements or improper.

② The iron sheet of the distribution box is too thin and the rigidity is poor, resulting in serious deformation between the shell and the door, and too large closing gap.

③ The models and specifications of electrical appliances installed in some boxes do not meet the design requirements.

④ There is no grounding and neutral busbar, or the specification of grounding and neutral busbar is too small to meet the use requirements.

⑤ Some distribution boxes have no isolation and blocking protection, and some protection boards are not equipped with insulating or flame retardant materials.

To solve the above problems, we can adopt:

① It is required to order in strict accordance with the design drawings and relevant specifications. The appearance inspection shall be carried out in time when receiving the goods, whether there is factory certificate, whether the nameplate is correct, whether the accessories are complete, whether the insulating parts have defects and cracks, and whether the coating is complete. Whether the model and specification of electrical appliances in the box meet the design requirements.

② Whether the application thickness of iron box of distribution box meets the requirements.

③ There is a grounding terminal board in the distribution box, which shall be connected with the box, and the working zero line terminal board shall be insulated from the box (except for the general distribution box). The terminal board shall be made of rectangular bus with a cross-section greater than 2 times of the large conductor in the box (but the small cross-section shall not be less than 60mm2 and the thickness shall not be less than 3mm). The material of terminal board is copper.