1.1 Faults caused by the influence of ambient temperature on low-voltage appliances
The low-voltage appliances in the distribution box are composed of fuses, AC contactors, residual current action protectors, capacitors and meters. The upper limit of ambient air temperature shall not exceed 40℃; The average ambient air temperature of 24h does not exceed 35℃; The lower limit of ambient air temperature shall not be lower than -5℃ or -25℃.
Rural grid transformation of the distribution box in the outdoor operation, it is not only under the direct sunlight to produce high temperature, at the same time, the operation of its own heat, so in the summer high temperature season, the temperature inside the box will reach more than 60℃, then the temperature greatly exceeds the environmental temperature specified by these electrical appliances.
1.2 Faults caused by product quality
During the transformation of rural power grid, due to the large number of distribution boxes needed and the short construction period, distribution box factory needed to supply low-voltage appliances urgently and in large quantity, which resulted in the phenomenon of not strict requirements on product quality, resulting in some products into operation soon after the failure. Such as some models of AC contactor in the distribution box shortly after operation, due to the contactor closing coil burned out, and can not run.
1.3 Faults caused by improper selection of electrical appliances in the distribution box
Due to the capacity selection of AC contactor is not very appropriate during manufacturing, AC contactor with the same capacity is installed on different outlet circuits, and the unbalance of three-phase load is not taken into account, and the current level of part of the outlet contactor is not selected on the basis of the normal model, and a current level selection is improved.
To improve the