What Is a Power Box?

The power box is mainly used to provide operating power for vacuum circuit breakers and other high-voltage switches. The power supply box adopts the input voltage 220V or 380V and is controlled by thyristor to regulate and rectify. It outputs DC. It has the characteristics of outputting DC voltage with multiple adjustable currents or AC voltage.

The power supply box is a control center that directs the various components in the power supply line to reasonably distribute electrical energy. It is a control link that reliably accepts the upper power supply and correctly feeds the load electrical energy. It is also the key to obtaining users' satisfaction with the power supply quality. Improving the operational reliability of power supply boxes is the goal of creating high-quality projects.

The power supply box is generally assembled in a closed or semi-closed metal cabinet or screen according to the electrical wiring requirements to form a low-voltage power supply box. During normal operation, the circuit can be switched on or off with the help of manual or automatic switches. In the event of malfunction or abnormal operation, the protection circuit is used to cut off the circuit or give an alarm. Various measuring parameters can be displayed by the measuring instrument, and some electrical parameters can be adjusted to indicate or signal the deviation from the normal working state.

The purpose of the power box is to reasonably distribute electrical energy, which is convenient for opening and closing the circuit. It has a high level of safety protection and can directly show the conduction state of the circuit. ^[1]

The power box is small in size, easy to install, special in technical performance, fixed in position, unique in configuration functions, not subject to site restrictions, widely used, stable and reliable operation, high space utilization, small footprint and environmental protection.

There are two types of commonly used power boxes: wooden and metal. Because metal power boxes have a higher level of protection, they are more often used in metal.

(1) Fixed panel type

(1) Failure caused by the influence of ambient temperature on low-voltage electrical appliances

The low-voltage electrical appliances in the power box are composed of fuses, AC contactors, residual current action protectors, capacitors, and meters. The upper limit of ambient air temperature does not exceed 40 ° C; the average value of ambient air temperature for 24h does not exceed 35 ° C; the lower limit of ambient air temperature is not lower than -5 ° C or -25 ° C.

The power box modified by the rural power grid operates outdoors. It not only generates high temperature when it is directly irradiated by sunlight, but also generates heat during operation. Therefore, in the high summer season, the temperature inside the box will reach 60 ° C or higher. Significantly exceeds the ambient temperature specified for these appliances.

(2) Failure caused by product quality

During the reconstruction of the rural power grid at that time, due to the large number of power supply boxes required and the short construction period, the power supply box factory needed to supply the low-voltage electrical appliances in a short time and in a large number, which resulted in a lack of strict requirements for product quality, which caused some The product failed shortly after it was put into operation. For example, some models of AC contactors cannot be operated because the contactor closing coil is burned out shortly after the power supply box is put into operation.

(3) Failure caused by improper selection of electrical appliances in the power box

Due to the improper selection of the capacity of the AC contactor at the time of manufacture, the AC contactors with the same capacity were installed for different outgoing circuits, and the imbalance of the three-phase load was not considered, and the current level of some of the outgoing contactors was not normal. Based on the model selection, a current level selection is increased. ^[3]