Faults caused by the influence of ambient temperature on low-voltage electrical appliances

The low-voltage electrical appliances in the distribution box are composed of fuses, AC contactors, residual current action protectors, capacitors and meters. These low-voltage electrical appliances are designed and manufactured in accordance with gb1497 basic standard for low voltage electrical appliances, and their normal working conditions are specified accordingly: the upper limit of ambient air temperature is not more than 40 ℃; The average value of ambient air temperature in 24h shall not exceed 35 ℃; The lower limit of ambient air temperature shall not be lower than -5 ℃ or -25 ℃.

The distribution box transformed by rural power grid operates outdoors. It is not only exposed to the direct sunlight to produce high temperature, but also generates heat during operation. Therefore, in the high-temperature season in midsummer, the temperature in the box will reach more than 60 ℃. At this time, the temperature greatly exceeds the specified ambient temperature of these electrical appliances, so the fault caused by overheating of electrical components in the distribution box will occur.

Faults caused by product quality

In the transformation of rural power grid, due to the large number of distribution boxes required and the short construction period, the distribution box factory needed the supply time and quantity of low-voltage electrical appliances, which resulted in the phenomenon of lax requirements for product quality, causing some products to fail soon after they were put into operation. For example, some models of AC contactors cannot operate because the closing coil of the contactor is burnt out soon after the distribution box is put into operation.

Faults caused by improper selection of electrical appliances in the distribution box

Due to the improper selection of AC contactor capacity during manufacturing, AC contactors with the same capacity are installed for different outgoing circuits, and the imbalance of three-phase load is not considered, and the current level of some outgoing contactors is not increased by one current level on the basis of the normal selection model, resulting in the burning out of AC contactors during operation in summer high temperature season.