1. Overview
Box-type substation, also known as pre-installed substation or pre-installed substation. Is a high-voltage switchgear, distribution transformer and low-voltage distribution device, according to a certain wiring scheme arranged into one of the factory prefabricated indoor and outdoor compact distribution equipment, that is, transformer step-down, low-voltage distribution and other functions organically combined together, installed in a moisture, rust, dust, rat, fire, anti-theft, heat insulation, fully enclosed, movable steel structure box. It is especially suitable for urban network construction and transformation, and it is a new substation that rises after civil substation. Box-type substation is suitable for mines, factories, oil and gas fields and wind power stations, it replaces the original civil distribution room, distribution power station, and becomes a new complete set of transformer and distribution equipment.
In recent years, the load density of low-voltage power supply is increasing, and the reliability and quality of power supply are also put forward high requirements. In this case, if a large-capacity substation is centered on the low-voltage power supply to the surrounding users, it will consume a lot of non-ferrous metals, and the power loss is very large, and the quality of power supply cannot be guaranteed. On the contrary, if the high voltage goes deep into the load center and the substation is built in the load center, the low-voltage power supply radius can be shortened, the power supply quality can be improved, the non-ferrous metals can be saved, and the power loss can be reduced. It is most suitable to build a box-type substation in the load center.
High-voltage/low-voltage pre-packed box substation (substation), also known as box substation or combined type substation (combined box substation), complete sets of substations, mobile substations, produced in the 1970s, there are a number of manufacturers in China. Its structure is basically a box-type structure, with high-voltage switch chamber, transformer chamber and low-voltage distribution switch chamber three parts, rated voltage of 10, 35kV, can be installed 1600kVA and below transformers. Its characteristics are: small footprint; Factory production, fast speed, good quality; The construction speed is fast, only the basic part of the site construction is needed; Beautiful appearance, can be coordinated with the residential area environment; Strong adaptability, interchangeability, easy to standardize and serialize; The maintenance workload is small, saving investment.
Therefore, the box-type substation has been valued and welcomed both abroad and at home, can be widely used, is a very promising electrical equipment, has been widely used in factories, mines, oil fields, ports, airports, stations, urban public buildings, concentrated residential areas, government units, schools, commercial halls and underground facilities and other places.
At present, there are many kinds of combined substations of different types in China, including outdoor type, indoor type, fully enclosed type, semi-enclosed type, with corridor type, without corridor type, combined type, fixed type, device type, dry transformer, oil immersed transformer, terminal power supply, ring network power supply, etc., which can meet the needs of different users. The layout of the high voltage, transformer and low voltage chambers is a mesh arrangement or a product separation scheme. High voltage chamber equipment components selected imported, domestic or imported ring network cabinet, load switch plus current limiting fuse, vacuum circuit breaker. The low-pressure chamber is composed of power, lighting, metering and reactive power compensation cabinets. Ventilation and heat dissipation are provided with fan, automatic temperature controller, and anti-condensation controller. The shell is mostly made of ordinary or hot-dip galvanized steel plate, aluminum alloy plate, and the skeleton is welded with shaped steel or bolted.
2. Classification
Box variation types can be divided into European, American and integrated. European box transformer is the transformer as a single part, set high voltage cabinet, transformer, low voltage cabinet trinity, according to a certain wiring scheme combined in one or several boxes to form a compact complete set of power distribution device. The box has two types of composition, namely, “eye” shape layout and “product” shape layout. The high and low voltage chamber arranged in the “mesh” shape is wider, which is convenient to realize the ring network power supply scheme of ring network or double power supply connection.
American box
The high voltage chamber of the European type transformer is generally composed of a high voltage load switch, a high voltage fuse and a lightning arrester, etc., which can be stopped for power transmission operation and have overload and short circuit protection. The low-voltage chamber is composed of low-voltage air switch, current transformer, ammeter, voltmeter, etc. Transformers are generally S9 or dry type.
The structure of the American box-type combination transformer is divided into two parts, the front is the wiring cabinet, the wiring cabinet includes high and low voltage terminals, high voltage load switch, plug-in fuse, high pressure tap changer operating handle, oil level gauge, oil temperature gauge, etc. The rear is the oil box and heat sink, transformer winding, iron core, high voltage load switch, plug-in fuse are in the tank body. The box adopts a fully sealed structure. The integrated box has recently been developed by domestic manufacturers and is not widely used. It is a double-layer structure, and the high and low pressure chambers are placed above the transformer room.
European-style, American-style and integrated box variants have advantages and disadvantages, the volume of European-style box variants is larger, high and low voltage switches and transformers are located in a large housing, poor heat dissipation conditions, need to install mechanical exhaust devices. Due to the direct external heat dissipation of the transformer cooling sheet, the heat dissipation conditions are relatively good, but its shape is worse than that of Europe, and its appearance is difficult to cooperate with the green environment such as residential quarters. The integrated box occupies less space, and the advantages and disadvantages are similar to the American box. In addition, the American-style, integrated box can only be manufactured in China with a capacity below 630kVA, and the European-style box can reach 1250kVA.
Ordinary box-type substation models are divided into three categories
(1) High-voltage switchgear model;
(2) dry transformer cabinet model;
(3) Low-voltage switchgear model.
The meaning of the first three letter symbols is:
Z-combined type; B- Substation; N(W)- indoor (outdoor, not included); X-box type; Y-mobile.
3. Basic Structure
The structure of box-type substation is related to the space required by various wiring equipment. Ring network, terminal power supply line scheme, the design is closed, semi-closed two categories, high and low equipment room is divided into operation corridor and no operation corridor structure, can meet the needs of six kinds of load switches, vacuum switches and other arbitrary combination. The high-voltage chamber, transformer chamber and low-voltage chamber are arranged in a zigzag pattern. According to the requirements of transportation, there are two kinds of integrated and sub-unit disassembly.
The box adopts steel sandwich (can be filled with asbestos) and composite board, and the top cover is sprayed with colored sand latex. The box is rainproof. For monitoring, maintenance and replacement of equipment, it is necessary to design a universal door, which can be opened by double or single doors. The transformer room is equipped with a structure of two sides of the door. The transformer compartment is provided with a track for the transformer to move (nameplate and danger sign are provided in the obvious place of the housing).
The high and low voltage side of the substation should be equipped with doors, and there is sufficient size, the door is pulled outward, the door has a handle, a lock, and a dark latch, the opening Angle of the door is not less than 90°, and the opening of the door has a corresponding chain. The high pressure side meets the requirements of “five defenses”. In the case of no power, a reliable grounding device is installed after the door is opened, and the live part can be repaired when there is no voltage signal indication. After the high and low pressure side doors are opened, there is a lighting device to ensure the safety of operation and maintenance.
The housing has ventilation holes and heat insulation measures, and heat dissipation measures can be used if necessary to prevent excessive internal temperature. The air temperature in the small room of the high and low voltage switchgear should not cause the temperature of the components to exceed the requirements of the corresponding standards. At the same time, measures are also taken to ensure that no condensation occurs in the interior when the temperature changes rapidly. When there is a vent, there should be a dust filter device.
The inlet and outlet modes of a box-type substation can be one of the following four types: overhead line entry and exit, cable entry and exit, overhead line entry and exit, and cable entry and exit.
High-voltage load switch series fuse is used in high-voltage receiving equipment of box-type substation. This scheme has been widely used in the field of distribution in foreign cities, especially as the high-voltage receiving protection scheme of box-type substation. This is mainly due to:
(1) This protection scheme can basically meet the load situation of most cases used in box-type substation, which can control and break the normal load current, and can withstand and protect the short-circuit fault.
(2) Due to its small size, it is easy to realize the high-pressure ring network scheme in a limited space, so as to better highlight the characteristics of the small size of the box-type station.
(3) The line is simple, the maintenance workload is small, especially suitable for the actual use of the box-type substation without being on duty
(4) The cost is greatly reduced. Circuit breaker cost is usually the same rated parameter load switch 2 ~ 3 times, the use of high-voltage load switch series fuse instead of circuit breaker highlights the box station’s own characteristics, increase the competitiveness with civil substation.
At present, almost all domestic production plants are using this high-voltage protection scheme, which is the development direction of high-voltage receiving equipment in box-type substation.
The common load switch plus fuse and ring power supply device of 10kv distribution unit of box-type substation are connected to the high voltage end of the transformer from the adjacent overhead line. The cable entry method can be cable or overhead insulated cable. When used as a public box-type substation, the low-voltage outlet of the box-type substation depends on the transformer capacity, generally no more than 4 times, no more than 6 times, and it can also be a total outlet, and then branch power supply to the nearby distribution room. When the box-type substation is used as an independent user, the primary power supply can be adopted.
At present, most of the box-type substations are equipped with lightning arresters as the overvoltage protection of transformers and other high-voltage equipment in the station.
The main switch on the low voltage side of the transformer in the domestic box substation is roughly DZl0, DWl0, DWl5 type 3 automatic switches, and the electrical appliances used on the low voltage side branch are roughly BM, BT series fuses and DZ, DW series automatic switches. When the transformer capacity of the box-type substation is 200 ~ 630kVA, DWl0 or DWl5 is used as the low-voltage main switch. When the capacity exceeds 800kVA, DWl5 switch should be selected as far as possible.
4. Introduction to common box transformers
American box type transformer is the transformer, load switch, protection fuse and other equipment unified design, transformer winding and iron core, high voltage load switch and protection fuse are in the same oil-filled box, there is no relatively independent high and low voltage switch cabinet. The box is fully sealed with concealed high-strength bolts and silica gel to seal the box lid. The low pressure chamber is separately arranged outside the fuel tank. The American box type is divided into front and back two parts, the front is high and low pressure operation interval, the operation interval includes high and low pressure bushing, load switch, no-load pressure regulating tap changer, plug-in fuse, pressure release valve, thermometer, oil level meter, oil injection hole, oil release valve, etc.; The rear is the box and heat sink.
The European box-type transformer (pre-installed substation) is a device that places high-voltage switchgear, distribution transformer and low-voltage distribution device in three different compartments and realizes electrical connection through cables or busbars. The high and low voltage switchgear is relatively independent and compact combination and pre-installed with the transformer in the box that can be lifted and transported, and the transformer room, high voltage room and low voltage room are equipped with independent doors, so its volume is larger than the American box type.
A buried transformer is a compact combined power distribution facility with transformers, high-voltage load switches and protective fuses installed in the tank and placed in the pit during installation. It has the characteristics of not occupying space, can be submerged in water for a certain period of time, maintenance-free, etc., which is conducive to saving the area of urban power distribution facilities, so it has a wide range of application prospects in the transformation and construction of urban network.