What are the Characteristics of Compact Substation? Introduction of Compact Substation

Compact substation, also known as compact substation or compact substation. It is a kind of high-voltage switchgear, distribution transformer and low-voltage power distribution device. It is a factory compact indoor and outdoor compact power distribution device arranged according to a certain wiring scheme, which is to organically combine functions such as transformer step-down and low-voltage power distribution. Together, they are installed in a moisture-proof, rust-proof, dust-proof, rodent-proof, fire-proof, theft-proof, heat-insulated, fully enclosed, and movable steel structure box, which is especially suitable for urban network construction and transformation. A brand new substation. The compact substation is suitable for mines, factories, enterprises, oil and gas fields and wind power stations. It replaces the original civil engineering power distribution room and power distribution station, and becomes a new type of complete power transformation and distribution device.

1. The development history of compact substation

The compact substation is suitable for residential quarters, urban public substations, bustling downtown, construction power supply, etc. Users can choose compact substations according to different conditions of use and load levels. Since the box type substation came out, it has developed extremely rapidly. In developed countries in Europe, it has accounted for 70% of distribution transformers, and in the United States it has accounted for 90%. With the rapid development of China's urban modernization and the continuous renewal and transformation of urban distribution networks, it will be widely used.

For compact substations, since the late 1970s, China has imported and imitated compact substations from France, Germany and other countries. The structure adopts high and low-voltage switch cabinets and transformers. This kind of compact substation is called European-style compact substation. , The image is likened to building a house for high and low voltage switch cabinets and transformers. Since the 1990s, China has introduced American compact substations, and structurally simplified the structure of load switches, ring network switches and fuses into transformer oil tanks and immersed in oil. The arrester also adopts oil-immersed zinc oxide arrester. The oil conservator is removed from the transformer, and the oil tank and radiator are exposed to the air. This kind of compact transformer is called an American-style compact transformer, and its image is compared to a box hanging next to the transformer.

2. The principle of compact substation

compact substation (compact substation for short) is a compact complete set of high-voltage switchgear distribution transformers, low-voltage switchgear, electric energy metering equipment and reactive power compensation devices combined in one or several boxes according to a certain wiring scheme. electric device. It is suitable for rated voltage 10/0.4KV three-phase AC system, as a circuit and distribution of electric energy.

Compared with the European-style compact transformer with the same capacity, the structure of the American-style compact transformer is more reasonable. Since the European-style compact substation installs the transformer and ordinary high-voltage electrical equipment in the same metal casing, the room temperature of the transformer is very high, which causes difficulty in heat dissipation and affects output; on the other hand, ordinary high-voltage load switches and fuses are used in the box. switchgear and low-voltage switchgear, so the volume of the European-style box transformer is relatively large. American-style compact transformers are different from European-style compact transformers in structure. From the perspective of layout, the low-voltage room, transformer room, and high-voltage room are not arranged in the shape of a word, but in the shape of a character. From a structural point of view, this compact transformer is divided into two parts, the front and the rear, and the front is the high and low voltage operation interval. Device, oil level gauge, etc.; the rear part is the oil tank and heat sink, and put the transformer winding, iron core, high voltage load switch and fuse into the transformer oil tank.

The arrester also adopts oil-immersed metal oxide arrester. The transformer cancels the oil conservator, and adopts the principle of constant volume of oil and air gap to design the sealed oil tank. The oil tank and radiator are exposed to the air, so there is no difficulty in heat dissipation. Molded case circuit breakers are used as the main circuit breaker and outlet circuit breaker for the low-voltage circuit breaker. Due to the simplified structure, the footprint and volume of this compact substation are greatly reduced. Due to its small size and only one side door, the required floor area is only 1/4 of the European compact substation, and the volume is only 1/4. It is 1/5-1/3 of the European box transformer with the same capacity. The high-voltage side of the American-style compact transformer is protected by a fuse, and the low-voltage side is protected by a plastic case automatic air circuit breaker, which is the same as the protection method of the 10kV distribution transformer in China. The high-voltage fuse protects the internal fault of the transformer, and the automatic air circuit breaker protects the over-current, short-circuit, and under-voltage faults of the low-voltage side line. The disadvantages of American box transformers. Because the load switch is immersed in the oil, the oil is carbonized and decomposed by the arc, and harmful gases such as acetylene are produced, which reduces the performance and caused accidents. No obvious break point can be seen, and maintenance is inconvenient. Because the low-voltage protection and measurement methods in the United States are different from those in China, the American-style box transformer itself does not have low-voltage protection and measurement. In order to meet the needs of domestic users, domestic compact substations are equipped with low-voltage power distribution cabinets on the low-voltage side. Since the compact inverter is exposed to the sun for a long time, it affects the heat dissipation of the molded case circuit breaker, so that the circuit breaker cannot normally break the load and short-circuit current, and it is easy to cause a fault on the high-voltage side.

3. The structure of compact substation

3.1 European compact transformer

3.1.1 Box structure:

The box body of European substation is composed of three parts: base, shell and top cover. The base is generally made of channel steel, angle steel, flat steel, steel plate, etc., which are assembled and welded or fixed with bolts; in order to meet the needs of ventilation, heat dissipation, and incoming and outgoing lines, strip-shaped holes and round holes of appropriate size should also be made at corresponding positions. shaped hole. The box shell, top cover channel steel, angle steel, steel plate, aluminum alloy plate, color steel plate, cement plate, etc. are bent, welded or connected with screws, hinges or related special accessories.

No matter what kind of material the box transformer shell is, it must have five anti-proof functions: sunscreen, rainproof, dustproof, rustproof, and small animals (such as snakes) to prevent entry according to the standard requirements. In order to prevent strong solar radiation in hot summer, the shell of the European-style substation is generally equipped with thermal insulation materials with low thermal conductivity as fillers. Commonly used fillers are: rock wool board, polystyrene foam, etc.

In the traditional "combined substation" with uniform design, the shell is generally filled with thermal insulation filler, which is no longer used by most designers, because: although the thermal insulation filler can prevent strong solar radiation in hot summer At the same time, it also hinders the dissipation of a large amount of heat generated during the operation of the transformer. Therefore, in addition to retaining the method of punching louver holes on the casing, the designers also adopt the method of increasing the heat dissipation area and strengthening air convection to dissipate heat. At the same time, it can also reduce manufacturing. cost.

Surface treatment of European-style box substations: There are many methods for surface treatment of European-style box substations. In northern China, traditional methods such as painting, baking, and plastic spraying are mostly used for treatment; in economically developed areas in southern China, in addition to the above methods, there are also Paste colored ceramic tiles on the outside of the shell of the cement board structure, or use methods such as veneering for surface treatment, especially the appearance of the compact substation placed in the residential area, which is more coordinated and unified with the style of the local buildings.

3.1.2 Structure of high voltage power distribution device:

The European-style compact high-voltage power distribution device can be divided into two types: terminal type and ring network type in terms of the incoming line method; it can be divided into two types in terms of the incoming line position: overhead incoming line from the top of the box body (traditional compact transformers use this method to compare Many) and the use of high-voltage cable trenches to enter and exit lines from the ground, which is a more common method used in modern designs.

There are many SF6 series load switches with SF6 gas as the arc extinguishing medium, and their cost is higher than that of FN-10 series high voltage load switches. This type of switch structure has fuses, without fuses, grounding switches, etc., but is generally equipped with a live display; the operating mechanism is generally manual, and there are also electric operations. With a fuse, when a short-circuit fault occurs in the circuit, it can automatically cut off the switch to protect the circuit, transformers, switches and other equipment.

There is also a vacuum switch with vacuum as the arc-extinguishing medium. This type of switch can be used alone or with a fuse, and it can also be used in series with the SF6 series load switch, but this will increase the cost. Requirements do not have to be used in this way.

High-voltage metering: In the high-voltage power distribution device, if the user has high-voltage metering requirements, a high-voltage metering cabinet must also be installed.

The power supply departments in various parts of China do not have uniform requirements for high-voltage or low-voltage metering issues. The power supply regulations in Northwest China stipulate that when the transformer capacity is greater than 160KVA, high-voltage measurement must be used; the switch of the high-voltage measurement cabinet must be controlled by the power supply department. The power supply departments in North China such as Beijing and Tianjin believe that the measurement of compact substations should be done on the low-voltage side. In this way, the reliability of power supply can be improved, the unstable factors caused by high-voltage measurement can be reduced, and the loss of the transformer itself can be converted into electricity bills. , is borne by the user.

The structure of high-voltage metering cabinets in compact substations generally consists of: CT, PT, and metering meters, remote control, and telemetry devices.

3.1.3 Transformer room structure:

European-style compact substations are equipped with independent transformer rooms, which are mainly composed of transformers, automatic temperature control systems, lighting and safety fences.

When the transformer is in operation, a large amount of heat will be generated in the box and dissipated to the transformer room. Therefore, the heat dissipation and ventilation of the transformer room should be considered in the design of the European-style box. When the transformer is in operation, a large amount of heat is continuously generated. The temperature in the transformer room continues to rise, especially when the ambient temperature is high, the temperature rises faster, so natural ventilation and heat dissipation alone often cannot guarantee the reliable and safe operation of the transformer; In addition to natural ventilation, temperature measurement protection is generally designed, and forced exhaust measures are used to solve the problem. The system is mainly composed of measuring devices, which can measure both the room temperature of the transformer and the temperature of the oil. Then through the manual and automatic control circuit, whether the exhaust fan needs to be put in or not is set and controlled according to the setting range of the reliable and safe operating temperature of the transformer.

In European-style compact transformers, the transformer can be either an oil-immersed transformer or a dry-type transformer. However, due to the high price of dry-type transformers, oil-immersed transformers should be preferred if the user has no special requirements to reduce manufacturing costs. cost. The capacity of the transformer is generally 100-1250KVA, and the maximum should not exceed 1600KVA.

3.1.4 Structural design of low-voltage chamber:

The low-voltage room of the European-style compact substation should be different in design structure according to the different usage occasions of industrial and mining enterprises or residential quarters. Generally, for European-style compact transformers used by industrial and mining enterprises, power supply and lighting power supply should be designed separately. When using low-voltage metering, under normal circumstances, the power supply bureau requires separate metering of lighting electricity, mainly because the unit price of lighting electricity is generally higher than that of power electricity. In the structural design of substations used in residential quarters, it is not necessary to consider the problem of power consumption.

The number of output channels of the low-voltage room of Eurovariant varies in structural design according to the size of the transformer capacity and the needs of users. The capacity of the transformer is small, and the number of output channels required by the user can be reduced; while the capacity of the transformer is large, and the number of input and output channels is required by the user, the design of more channels can be considered, and the layout can also be considered in the form of operation with corridors.

3.2 American box substation

China's compact transformers were originally developed from European-style compact transformers, and their volume is often relatively large. With the opening of China's foreign economy and the vigorous development of the market economy, in the 1990s, American-style compact transformers entered the Chinese market, and achieved rapid development in the Chinese market with its unique characteristics. From south to north, from east to west in China, this kind of American-style compact substation can be seen almost everywhere, and most of them are imitated products of domestic manufacturers, and their quality can be said to be uneven. Through these years of application and practice, it is necessary to carefully analyze the American box substation combined with China's national conditions, and give a correct positioning, so as to promote the technology and market development of China's box substation.

Main features of American box transformer:

Strong overload capacity, allowing 2 times overload for 2 hours, 1.6 times overload for 7 hours without affecting the life of the box change.

The elbow-type plug connector is adopted, which is very convenient for the connection of high-voltage incoming cables, and can be used as a load switch in an emergency, and can be plugged and unplugged with power on.

Double fuse protection is used, and the plug-in fuse (BAY-o-net) is a dual-sensitive fuse (temperature, current) to protect the short-circuit fault that occurs on the secondary side of the box transformer. The back-up current-limiting protection fuse (ELSP) protects the internal fault of the compact transformer and is used to protect the high-voltage side.

Transformers generally use high ignition point oil (FR3).

All components such as the fuse for high-voltage load switch protection are placed in the same oil tank as the transformer core and winding.

Anti-corrosion and protection of American box transformer shell:

American-style box substation, its box adopts anti-corrosion design and special painting treatment, which can be applied to various harsh environments, such as areas with frequent storms and high pollution. Before painting, the box body undergoes eight pretreatment processes, and then seven painting and baking processes are completed, which shows its cautious attitude towards anti-corrosion. However, the domestically produced American-style box substation shells are almost not subjected to special treatment. Basically, they are treated with electrostatic spraying after pickling, and some companies even do not even carry out pickling treatment. It is conceivable how the anti-corrosion ability of its shell is. Even if it is electrostatic spraying treatment, some dead corners often appear when the bottom surface is treated, and it is difficult to spray powder on these untreated parts by electrostatic spraying, so there will inevitably be hidden dangers of corrosion. Since the box substation has to work in the outdoor environment of wind, rain and sun for many years, if the surface treatment is not good, the corrosion will be very serious. This problem is very important, and it has been a subject of great concern, attention and research in China for decades, so many manufacturers use some other technologies to solve this problem. Regarding protection, the transformer oil tank and cooling fins of the American-style compact substation are partly exposed outside, the purpose of which is to improve the heat dissipation conditions. However, because it is directly exposed to sunlight, whether it will affect the temperature rise under the heat radiation of sunlight has not been introduced in detail. In addition, the exposed parts are easily damaged by impacts and knocks from external forces. If it is damaged, a large amount of transformer oil will be lost, and the consequences will be unimaginable. Therefore, some domestic manufacturers wrap a layer of steel plate on the heat sink to increase the protection ability.

High voltage load switch of American box transformer:

The load switch of the American box transformer is put into the transformer oil tank. The oil-immersed three-phase linkage switch can be divided into two positions (terminal type) and four positions (ring network type). Since the load switch is placed in the transformer oil tank, its closing position can only be indicated by the external operation panel. To judge, and its operation is carried out through a special insulating operating rod, so its operation is more complicated. From this point of view, its operation is very inconvenient. In addition, because the breaking contact of the load switch (that is, the obvious breaking point) cannot be seen, it gives people a feeling of uneasiness after breaking. In addition, once the load switch breaks down, it will be very difficult to replace and repair it. The load switch generally adopts a vacuum circuit breaker.

About the maintenance of American box transformer

After the installation and use of American-style compact transformers, there is basically no need for maintenance. However, due to various reasons for domestically produced products, the maintenance of compact transformers is indispensable.

Due to the technical problems of the surface treatment of the shell, the corrosion inspection should be strengthened;

The oil filled in the oil tank of American box substation is generally FR3 insulating oil, its ignition point can reach 312°C, and it has excellent electrothermal characteristics, high insulation strength, good lubricity, strong arc extinguishing ability, non-toxic, and can be biodegraded. Hazards to the environment and health are thus minimized. FR3 insulating oil does not form sediment like traditional mineral oil, and most of the domestically produced American box substations are filled with 25# ordinary mineral oil. In addition, in general, the upper part of the oil tank of the American box transformer is filled with inert gas to prevent the moisture in the air from being exchanged into the oil. However, the domestic American-style box substation may not have an enterprise to carry out this work. Over time, the performance of the oil will decrease, and its sealing performance cannot meet the requirements of 7 psig, so the oil must be changed regularly.

American box transformers have no oil temperature protection, only a thermometer to display the oil temperature, when the oil temperature is too high, rely on plug-in fuses for protection, and a pressure release valve to release too much pressure in the oil tank. Therefore, regular checks should be made to see if the fuse is functioning properly in both cases, and if there is any oil leakage from the housing.

Since the fuel tank of the American box substation is exposed outside, it should be inspected frequently to prevent oil leakage due to damage caused by external collisions.

3.3 Domestic box substation

Compared with the American-style compact substation, the domestic compact substation has added a grounding switch and lightning arrester, and there is a mechanical interlock between the grounding switch and the main switch, which can ensure the absolute safety of the person during the maintenance of the compact substation. Domestic box substation uses one fuse for each phase instead of the two fuses of American box substation for protection. Its biggest feature is that when any phase fuse is blown, it will ensure that the load switch trips and cuts off the power supply, and only the fuse needs to be replaced. After that, the main switch can be closed, which is not available in the American box substation.

Domestic compact substations generally adopt a structure in which each unit is independent of each other. There are transformer rooms, high-voltage switch rooms, and low-voltage switch rooms respectively, which are connected by wires to form a complete power supply system.

The transformer room is generally placed at the rear. In order to facilitate the user's maintenance, replacement and capacity increase, the transformer can be easily pulled out from the box or hoisted from the upper part. Since the transformer is placed in the casing, the favorable factor is that it can prevent the temperature rise caused by direct sunlight on the transformer, and it can also effectively prevent external force collisions, impacts, and touch induction accidents; the disadvantageous factor is that the heat dissipation of the transformer is raised higher requirements. An independent closed high-voltage switchgear is installed in the high-voltage switchgear room. In the cabinet, there are generally installed gas-generating, compressed-air or vacuum-type load switch-fuse combination appliances. The high-voltage fuse installed on it can ensure that any phase fuse is blown. The main switch can be opened to avoid phase loss operation. In addition, there is a grounding switch, which is interlocked with the main switch, that is, the grounding switch can only be closed after the main switch is separated, and the main switch cannot be closed after the grounding switch is closed, so as to ensure safety during maintenance. There is also a high-voltage arrester in the cabinet, and the operation of the whole switch is very convenient. Only the special matching handle is used to realize the closing and breaking of all switches. At the same time, the opening and closing state of the main switch can be observed through the transparent window.

Low-voltage switchgear: Generally, the low-voltage switchgear is equipped with the main switch and each distribution branch switch, low-voltage surge protector, voltage and total current, and instrument display of branch current. Measures for monitoring the oil temperature on the upper layer of the transformer. When the oil temperature reaches a dangerous temperature, it can automatically stop working on the low pressure side (disconnect the load on the low pressure side). Of course, its action value can be set according to requirements.

Shell and protection: Each switch cabinet of the domestic compact substation is made into an independent cabinet and installed in the shell, which can be easily replaced and maintained, and also improves the protection ability and safety. Its steel shell is anti-corrosion treated by special process, so that its protection ability can reach more than 20 years. At the same time, the upper cover adopts a double-layer structure to reduce the heat radiation of the sun, and its appearance can be matched with various colors in harmony with the use environment according to user requirements, so as to achieve the effect of matching with the natural environment.

Other aspects: Both American-style compact transformers and domestic-made compact transformers can increase the functions of metering compensation and other aspects, but the volume is slightly increased. In addition, domestic compact transformers can also use elbow-type cable heads for incoming cable insertion. By the way, it is pointed out that the transformers of domestic compact substations generally use S9 fully sealed low-loss transformers, while some foreign products have used amorphous alloys as transformer cores in order to reduce losses. In China, amorphous alloy transformers have been produced in small batches. In other words, the one-time investment is relatively large, but the economic benefits it brings are still considerable.

To be more precise, the domestic horizontal box change should be called the European and American integrated box change, which is more appropriate. The appearance of the horizontal compact transformer is similar to that of the European-style compact transformer, but its volume is much smaller than that of the European-type compact transformer and slightly larger than that of the American-type compact transformer. This is because the transformer, load switch and low-voltage outlet of the horizontal compact transformer are basically the same as the American compact transformer, but it has an independent transformer room. Since the high and low voltage outlets are on the side walls, the transformer room does not need to consider facilities such as guardrails. Due to the small size and compact structure of the horizontal box transformer, some designers have greatly simplified the design of the top cover (no heat insulation layer, etc.), and only retained the natural ventilation cooling mode. The heat dissipation level of the transformer placed in the box variant is greatly reduced.

4. Features of compact substation

The compact substation is mainly composed of electrical units such as multi-circuit high-voltage switch system, armored busbar, substation integrated automation system, communication, telecontrol, metering, capacitance compensation and DC power supply. It is installed in a moisture-proof, rust-proof, dust-proof, Anti-rat, fireproof, anti-theft, heat insulation, fully enclosed, movable steel structure box, mechanical and electrical integration, fully enclosed operation, mainly has the following characteristics:

Advanced technology, safe and reliable

The box part adopts domestic leading technology and technology. The outer shell is generally made of galvanized steel plate. The frame is made of standard container materials and manufacturing technology. Fireproof insulation materials, air conditioning and dehumidification devices are installed in the box, the operation of the equipment is not affected by the natural climate environment and external pollution, and it can guarantee normal operation in the harsh environment of -40℃～+40℃. The primary equipment in the box adopts fully enclosed high-voltage switchgear (such as: xgn type), dry-type transformer, dry-type transformer, vacuum circuit breaker, spring operating mechanism, rotary isolating switch and other domestic technology-leading equipment, and the product has no exposed live parts. Fully enclosed and fully insulated structure can completely achieve zero electric shock accidents. The whole station can realize oil-free operation with high safety. The secondary use of microcomputer integrated automation system can realize unattended.

high degree of automation

The intelligent design of the whole station, the protection system adopts the microcomputer integrated automation device of the substation, and the scattered installation can realize "four remotes", that is, telemetry, remote signaling, remote control, and remote adjustment. Each unit has an independent operation function and complete relay protection functions , can set the operating parameters remotely, control the humidity and temperature in the cabinet, and remotely smoke alarm to meet the requirements of no one on duty; it can also realize remote monitoring of images according to needs.

factory prefabrication

When designing, as long as the designer makes a design of the main wiring diagram and equipment outside the box according to the actual requirements of the substation, he can choose the specification and model of the box transformer provided by the manufacturer. The construction is factory-like, which shortens the design and manufacturing cycle; on-site installation only requires box positioning, cable connection between boxes, outgoing cable connection, protection setting verification, transmission test and other work that needs to be debugged. It only takes about 5-8 days, which greatly shortens the construction period.

Flexible combination

Due to the relatively compact structure of the compact substation, each box constitutes an independent system, which makes the combination method flexible and changeable. On the one hand, we can all use compact substations, that is to say, all 35kv and 10kv equipment are installed in the box, and the composition Full box type substation; it can also only use 10kv switch box, 35kv equipment installed outdoors, 10kv equipment and control and protection system installed in the box, for this combination method, it is especially suitable for the old station transformation in the transformation of rural power grid, that is, the original 35kv The equipment does not move, and only one 10kv switch box is installed to meet the unattended requirements. In short, there is no fixed combination mode for the compact substation, and the user can freely combine some modes according to the actual situation to meet the needs of safe operation.

Save investment and get quick results

Compared with conventional substations of the same scale, compact substations reduce investment by 40% to 50%. Based on the calculation of 35kv single main transformer and 4000kva-scale substations, compact substations save more than 1 million yuan in civil engineering (including land acquisition costs) compared with conventional substations; From the perspective of completion and commissioning, it is conservatively estimated that each station will be put into operation 4 months in advance. If the average load is 2000kw, the profit from electricity sales will be 0.10 yuan/kw.h, and the net profit will increase by more than 600,000 yuan in three months; from the perspective of operation, In the compact substation, due to the selection of advanced equipment, especially the operation of oil-free equipment, the problem of equipment leakage in conventional substations has been completely solved. The substation can implement condition-based maintenance, reduce maintenance workload, and save annual The operation and maintenance cost is about 100,000 yuan, and the overall economic benefits are considerable.

Small footprint

Taking the 4000kva single main transformer scale substation as an example, the construction of a conventional 35kv substation needs to occupy an area of about 3000m, and large-scale civil engineering is required; and the compact substation is selected, the main transformer box and the switch box are two boxes The floor area of the body can be as small as 100m, including 35kv and other equipment, the total floor area is up to 300m, which is only 1/10 of the area occupied by the same scale substation, and can be installed and put into production by making full use of the center of the street, square and factory corner , in line with the national policy of saving land.

nice appearance

The box shell adopts galvanized steel plate and container manufacturing technology, and the appearance design is beautiful. On the premise of ensuring the reliability of power supply, by selecting the shell color of the compact substation, it is very easy to coordinate with the surrounding environment. It is especially suitable for urban construction, such as : In densely populated areas such as urban residential areas, stations, ports, airports, parks, green belts, etc., it can be used as a fixed substation or a mobile substation, and has the functions of embellishing and beautifying the environment.

The shell of the compact substation is made of steel plate or alloy plate, equipped with a double-layer top cover, which has good heat insulation. The shell and frame are all treated with anti-corrosion, which is suitable for long-term outdoor use. The shape and color can be coordinated with the environment. It is easy to install. There is a cable room under the foundation of the compact substation, and a manhole is provided in the low-voltage room to enter the cable room for work. In terms of volume, European-style compact transformers are relatively large due to the internal installation of conventional switch cabinets and transformers. The American-style compact transformer is smaller in size due to the integrated installation.

The high-voltage side of the European-style compact transformer is protected by a load switch and a current-limiting fuse. When a one-phase fuse is blown, use the striker of the fuse to open the load switch in three phases at the same time to avoid phase-open operation. The load switch is required to have the ability to cut off the transfer current, and the low-voltage side is protected by a load switch plus a current-limiting fuse. The high-voltage side of the American-style compact transformer is protected by a fuse, while the load switch only performs the function of switching and cutting off the high-voltage load current, and its capacity is small. When a phase fuse blows on the high-voltage side, the voltage on the low-voltage side will drop, and the undervoltage protection or overcurrent protection of the plastic case automatic air switch will operate, and low-voltage operation will not occur. In terms of product cost, the cost of European-style boxes is high. From the perspective of product price reduction space, there is still a large room for price reduction in American-style compact transformers. On the one hand, the three-phase five-pillar core of American-style compact transformers can be changed to three-phase three-pillar cores. On the other hand, the high-voltage part of American-style compact transformers can be modified from The inside of the transformer oil tank is moved to the outside of the oil tank, occupying the space of the high voltage room.

5. Installation and operation of compact substation

The door of the compact substation box should open outwards, and there should be handles, hidden latches and locks, and the hidden latches and locks should be rust-proof. The transformer room should be based on natural ventilation, and the relationship curve between the temperature in the box and the output of the transformer is given. The transformer room can be equipped with a room temperature monitoring device and a self-starting ventilation cooling device as needed to ensure that the transformer operates at full load under specified environmental conditions. The transformer should be accessible from the top or side door of the box. The noise level of the compact substation should not be greater than the specified transformer noise level. Regardless of whether the box shell is made of metal or non-metallic materials, the metal frame of the box body should be well grounded, with a grounding terminal and marked with a grounding symbol.

The compact substation is mainly cooled by natural wind circulation. Therefore, no illegal piles can be placed around it, especially the transformer room door should not be blocked, and the attachments on the ventilation holes of the shutters should be removed frequently to ensure that all electrical equipment does not exceed the maximum allowable temperature. After the low-voltage circuit breaker trips, the cause of the trip should be checked before trial delivery. If the transmission is unsuccessful, the cause of the fault must be thoroughly searched for, and power can be transmitted only after troubleshooting to prevent the expansion of the accident. Zinc oxide surge arresters should be installed in the high-voltage power distribution room of compact transformers, and the installation method must be convenient for testing and disassembly and replacement.

The compact substation grounding and zero line share a grounding network. The grounding grid is generally grounded with ground piles at the four corners of the foundation, and then connected into one. There must be two reliable connections between the compact substation and the grounding grid. After the compact substation is in operation, the ground connection should be checked frequently, because it is not loose or rusted. Regularly measure the grounding resistance value, and the grounding resistance should not be greater than 4Ω. The ring network switch, transformer, lightning arrester and other equipment in the high-voltage power distribution device of the compact substation should be inspected and maintained regularly, and defects should be repaired in time, and insulation preventive tests should be carried out regularly. If the compact substation has been out of service for more than 3 months, all preventive tests should be carried out before it is put into operation. To replace a high-voltage fuse with no breaking capacity, the transformer must be powered off, and the mechanical interlock must be released correctly during operation, and an insulating operating rod should be used. All incoming and outgoing cable holes in compact substations should be sealed to prevent small animals from entering and causing accidents.

The floor of the compact substation should be placed in a higher place, not in a low-lying place, so as to prevent rainwater from pouring into the box and affecting the operation of the equipment. When pouring the concrete platform, a gap should be left on the high and low voltage side to facilitate the laying of the cable entry and exit lines. When excavating the foundation, if the ground is piled up with garbage or humus, it is necessary to dig out solid soil, then backfill with better soil quality and compact it, and then fill with composite soil or ballast to ensure a stable foundation.

6. Maintenance of compact substation

In terms of installation, acceptance, handover test, test run, operation and maintenance, compact substations should abide by the regulations required by the power department. Attention should also be paid to the following items: when receiving the goods, the user should check carefully in accordance with the relevant regulations. For products that are not to be installed immediately, they should be stored in an appropriate place according to the normal use conditions. The product should be hoisted from the bottom with a special spreader. Place the product horizontally on the pre-made foundation, install four anchor bolts (the second watering method can be used), and then seal the gap between the product base and the foundation with cement sand paddle to prevent rainwater from entering the cable room. The high and low voltage cables are connected through the bottom sealing plates of the high and low voltage chambers. The gap between the cable and the conduit is sealed and waterproof. Whether the high-voltage side of the compact substation adopts overhead incoming lines or cable incoming lines, clearly visible fractures (such as drop-out fuses, etc.) of the high-voltage side incoming lines should be set near the substation. In this way, it can be clearly shown to the maintenance operators whether there is electricity in the substation. To ensure the safety of maintenance operators. After the product is installed in place, reliable grounding should be done: the two main grounding terminals on the channel steel of the base of the power station, the neutral point and shell of the transformer, and the lower pile head of the lightning arrester should be directly grounded by the installation department. The grounding of the place should share a set of grounding devices, the grounding resistance should be less than 4 ohms, and there should be no less than two leads from the grounding grid to the grounding lead.

After the compact substation is installed or repaired, the following inspections and tests should be carried out before it is put into operation. After the product is installed or repaired, the following inspections and tests should be carried out before it is put into operation. Whether the substation is clean. Whether the operating mechanism is flexible. Whether the on-off of main electrical appliances is flexible and reliable. Whether the on-off of electrical auxiliary contacts is reliable and accurate. Whether the meter and relay action are accurate. Whether the transformation ratio and wiring polarity of the instrument and transformer are correct. Whether all electrical installation nuts are tightened, and whether the installation is firm and reliable. Whether the bus connection is good, its supporting insulator, and whether the clamping parts are installed reliably. Whether the setting value of the electrical appliance meets the requirements, and whether the specification of the melting core of the fuse is correct. Whether the contacts of the main circuit and the auxiliary circuit meet the requirements of the electrical schematic diagram. The resistance of the product's internal protective grounding system should be less than 0.01 ohms. Each part should be subjected to a withstand voltage test according to the corresponding voltage level.

All components in the compact substation are maintained according to their respective technical requirements. If the selected transformer is oil-immersed, oil sample analysis and inspection should be carried out at least once a year according to regulations. For high-voltage switchgear in operation, after 20 times of on-load or 2000 times of off-load opening and closing operations, the condition of the contacts and the degree of wear of the arc extinguishing device should be checked, and any abnormality should be repaired or replaced in time. After the low-voltage switchgear trips automatically, the cause of the trip should be checked and analyzed, and it can only be put into operation after queuing up for failure. The lightning arrester should be tested once a year before the thunderstorm season. When overhauling high-voltage switchgear or overall maintenance, the incoming power of the substation must be cut off first.

7. Application prospect of compact substation

The compact substation is the main direction of the current rural power network transformation and the construction of substations in the future, but there are still some deficiencies in some aspects, specifically in:

7.1 Fire prevention issues: compact substations are generally fully sealed and unattended. Although all equipment operates without oil and is equipped with a remote smoke alarm system, there are still fire hazards in the box, such as cables and compensation capacitors. Fire is not conducive to ventilation and fire fighting, so the design of automatic fire extinguishing system should be considered, but this will increase the manufacturing cost of the compact substation.

7.2 Expansion problem: Due to the limited volume and manufacturing cost of the compact substation, the expansion margin of the outgoing line interval is small. If you want to add 1 to 2 outgoing line intervals in the original box, it is more difficult, and you must add another box to do it. arrive.

7.3 Maintenance problem: Due to the manufacturing cost and box volume limitation of the compact substation, the maintenance space of the compact substation is small, which is not conducive to equipment maintenance, especially emergency repairs. This is a congenital deficiency of the compact substation. Insurmountable shortcomings.

In short, looking forward to the future, compact substations will be widely used in my country's vast cities, rural areas, industrial and mining enterprises, and public building facilities. It will be used by more and more people with its advantages of high quality and low price, making my country's The level of power grid operation has reached a new level.