Box-type substation

Box-type substation (abbreviated as box-type substation) is suitable for residential areas, urban public substations, bustling downtown areas, construction power supplies, etc. It is a kind of high-voltage switchgear, power transformer, low-voltage switchgear, electric energy metering equipment and reactive compensation device installed in a compact box according to certain requirements, used for lines and distribution of electric energy.

Structure of box-type substation:

1. The box-type substation shell must have five protection functions according to standard requirements, including sun protection, rain protection, dust protection, rust protection, and prevention of small animals (such as snakes). The shell material can be stainless steel plate, cold-rolled steel plate, aluminum alloy plate, color steel plate and cement plate. The box body consists of three parts: base, shell and top cover. The base is generally welded or fixed with bolts using channel steel, angle steel, flat steel, steel plate, etc.; in order to meet the needs of ventilation, heat dissipation and inlet and outlet lines, strip holes and circular holes are opened at the corresponding positions. The box shell and top cover can be bent, welded or connected with screws, hinges and related special accessories by channel steel, angle steel, steel plate, aluminum alloy plate, color steel plate, cement plate, etc. In order to prevent strong sunlight radiation in hot summer, the top is equipped with insulation materials with low thermal conductivity as fillers, commonly used rock wool board, polystyrene foam, etc. However, in the traditional "combined substation" with unified design, most designers no longer use the method of filling the shell with insulation fillers, because although it can prevent sun exposure, it still hinders the heat dissipation of the transformer. Therefore, in addition to retaining the louver holes on the shell, the heat dissipation area is increased and the air convection is strengthened to dissipate heat, while reducing the manufacturing cost.

2. The high-voltage distribution device of the box transformer is divided into two types: terminal type and ring network type in terms of the incoming line mode; in terms of the incoming line direction, it can be divided into overhead incoming lines from the top of the box (mostly used in traditional box transformers) and underground incoming and outgoing lines using high-voltage cable trenches (commonly used in modern designs). There are many SF6 series load switches with SF6 gas as arc extinguishing medium, but the cost is higher than FN12 series high-voltage load switches. This type of switch has various structures, including with fuses, without fuses, grounding switches, etc., and is generally equipped with live displays. The operating mechanism is mostly manual and electric. The switch protection equipment with fuses can automatically cut off when the circuit is short-circuited. There are also vacuum switches with vacuum as arc extinguishing medium, which can be used alone, with fuses, or in series with SF6 series load switches, but it will increase the cost. Users do not need to use them in this way if they have no special requirements. If the user has high-voltage metering requirements, the high-voltage distribution device of the box-type transformer must also be equipped with a high-voltage metering cabinet, and its structure is generally composed of CT, PT, metering meters, remote control, and telemetry devices. However, the metering of the box-type substation should be based on the low-voltage side, which can improve the reliability of power supply and reduce unstable factors. The transformer loss can be converted into electricity charges borne by the user.

3. The box-type transformer is equipped with an independent transformer room, which is mainly composed of a transformer, an automatic temperature control system, lighting, and safety guardrails. The transformer will emit a lot of heat when it is running, so the heat dissipation and ventilation issues are the key points of the box transformer design. The heat generated by the operation of the transformer will increase the indoor temperature, especially when the ambient temperature is high. Natural ventilation alone often cannot ensure reliable and safe operation. In addition to the use of natural ventilation for small capacity, temperature measurement protection is generally designed and forced exhaust measures are used to solve the problem. The system mainly consists of a measuring device that can measure the room temperature and oil temperature of the transformer, and control the exhaust fan input according to the set range through manual and automatic control circuits. The transformer can be selected as oil-immersed or dry-type. Because the dry type is expensive, users generally prefer oil-immersed type to reduce costs without special requirements. The capacity is generally 100-1250KVA, and the maximum does not exceed 1600KVA.

4. The low-voltage room of the box transformer has different design structures according to the different use occasions of industrial and mining enterprises or residential areas. The box transformers used in industrial and mining enterprises should be designed separately for power supply and lighting power supply. When measuring low voltage, the power supply bureau requires separate metering of lighting electricity because the unit price of lighting electricity is higher than that of power electricity. The substation used in residential areas does not need to consider the problem of power electricity. The number of output routes in the low-voltage room varies according to the capacity of the transformer and user needs. If the capacity is small and the demand is small, fewer routes can be set; if the capacity is large and the demand is high, more routes can be set. It can also be laid out in a corridor operation format.