Mobile Substation - Advanced Technology, Safe and Reliable

The mobile substation (mobile box-type substation) product is fully sealed and fully insulated, and the personal safety is reliably guaranteed. It is small in size and compact in structure (the product occupies only 1/3 of the same capacity as the European-style box-type substation), and it is convenient and flexible to install. , can be used for both the ring network and the terminal, the conversion is convenient, and the reliability of the power supply is greatly improved.

1. Introduction of mobile substation

Mobile substation is a kind of high-voltage switchgear, distribution transformer and low-voltage power distribution device. It is a factory prefabricated indoor and outdoor compact power distribution equipment arranged according to a certain wiring scheme. Combined together, they are installed in a moisture-proof, rust-proof, dust-proof, rodent-proof, fire-proof, theft-proof, heat-insulating, fully enclosed, and movable steel structure box, which is especially suitable for urban network construction and transformation. A brand new mobile substation. The box-type 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.

2. The development history of mobile substation

The mobile substation is suitable for residential quarters, urban public mobile substations, bustling downtown, construction power supply, etc. Users can choose box-type 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 mobile substations, since the late 1970s, China has imported and imitated box-type substations from France, Germany and other countries. The structure adopts high and low-voltage switch cabinets and transformers. This kind of box-type substation is called European style. The box transformer is likened to building a house for high and low voltage switch cabinets and transformers. Since the 1990s, China has introduced American box-type 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 box-type transformer is called an American-style box-type transformer, and its image is compared to a box hanging next to the transformer.

3. The principle of mobile substation

The mobile substation (referred to as box-type substation) is a compact type that combines high-voltage switchgear distribution transformers, low-voltage switchgear, electric energy metering equipment and reactive power compensation devices in one or several boxes according to a certain wiring scheme. Complete set of power distribution equipment. 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 box-type transformer with the same capacity, the structure of the American-style box-type transformer is more reasonable. Since the European-style box-type 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 box-type transformers are different from European-style box-type 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 box-type 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 box-type 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 box-type substation, and the volume is only 1/4. It is 1/5-1/3 of the European-style box transformer with the same capacity. The high-voltage side of the American-style box-type 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 box-type substations are equipped with low-voltage power distribution cabinets on the low-voltage side. Since the box-type 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.

4. Structure of mobile substation

Domestic box-type 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 box-type 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 box-type transformers and domestic-made box-type transformers can increase the functions of metering compensation and other aspects, but the volume is slightly increased. In addition, domestic box-type transformers can also use elbow-type cable heads for incoming cable insertion. By the way, it is pointed out that the transformers of domestic box-type 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 box-type transformer is similar to that of the European-style box-type transformer, but its volume is much smaller than that of the European-type box-type transformer and slightly larger than that of the American-type box-type transformer. This is because the transformer, load switch and low-voltage outlet of the horizontal box-type transformer are basically the same as the American box-type 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. Its heat dissipation becomes a problem worthy of discussion.

5. Characteristics of mobile substation

The box-type substation is mainly composed of electrical units such as multi-circuit high-voltage switch system, armored busbar, mobile 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:

5.1 Advanced technology, safe and reliable

The box part adopts the current 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. Fire-proof and heat-insulating materials are used, and air-conditioning and dehumidification devices are installed in the cabinet. The operation of the equipment is not affected by the natural climate environment and external pollution, and can guarantee normal operation in the harsh environment of -40°C ~ +40°C. 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.

5.2 High degree of automation

The intelligent design of the whole station, the protection system adopts the microcomputer integrated automation device of the mobile 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.

5.3 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 mobile 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.

5.4 Flexible combination

Due to the relatively compact structure of the box-type substation, each box constitutes an independent system, which makes the combination method flexible and changeable. On the one hand, we can all use box-type 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 box-type substation, and the user can freely combine some modes according to the actual situation to meet the needs of safe operation.

5.5 Save investment and get quick results

Compared with conventional substations of the same scale, box-type substations reduce investment by 40% to 50%. Based on the calculation of 35kv single main transformer and 4000kva-scale substations, box-type 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 box-type 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 mobile 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.

5.6 Small footprint

Taking the 4000kva single main transformer scale mobile substation as an example, the construction of a conventional 35kv mobile substation needs to occupy an area of about 3000m, and large-scale civil engineering is required; and the box-type 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 mobile 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.

5.7 Beautiful 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 box-type 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 box-type 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 box-type substation, and a manhole is provided in the low-voltage room to enter the cable room for work. In terms of volume, European-style box-type transformers are relatively large due to the internal installation of conventional switch cabinets and transformers. The American-style box-type transformer is smaller in size due to the integrated installation.

The high-voltage side of the European-style box-type 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 box-type 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 box-type transformers. On the one hand, the three-phase five-pillar core of American-style box-type transformers can be changed to three-phase three-pillar cores. On the other hand, the high-voltage part of American-style box-type 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.

6. Operating procedures for mobile substations

6.1 Transformer operation

6.1.1 Under the rated conditions of use, the transformer can operate at a constant capacity throughout the year.

6.1.2 The oil temperature of the upper layer of the transformer should not exceed 85 degrees, and the temperature rise limit is 60 degrees.

6.1.3 The load of each winding of the transformer shall not exceed the rated value.

6.1.4 When the three-phase load of the transformer is unbalanced, the load of the maximum current item should be monitored.

6.1.5 Allowable operation modes of transformers:

a. The applied primary voltage of the transformer can be higher than the rated voltage, generally not more than 5% of the rated voltage of the operating tap.

b. When the transformer is running, the gas relay protection should be put into signal and connected to trip.

c. Before putting the transformer into operation, the on-duty personnel should check carefully to confirm that the transformer is in good condition and has live operation conditions (whether the grounding wire is removed, check the position of the tap changer and measure the insulation resistance).

d. After overhaul, accident repair and oil change, it should be kept still for 48 hours, and it can be put into operation after the air bubbles in the oil are eliminated.

e. When the pressure releaser of the transformer generates extreme pressure during operation, the releaser will release automatically. After the oil tank pressure is normal, the valve cover of the releaser should be automatically closed. If the releaser moves, the valve cover will lift up the indicating rod, which must be manually pressed to reset. At this time, the micro switch acts, and the wrench must be moved to reset the machine, so as to send a signal for the next action. The releaser contact should act on the signal.

6.1.6 The transformer should be shut down immediately in the following situations:

a. The internal sound is loud and uneven, accompanied by cracking and electric shock sounds.

b. The oil temperature exceeds 105 degrees.

c. When the load and cooling device are normal, the temperature rises abnormally and quickly.

d. The transformer has serious oil leakage, and the oil level drops sharply.

e. Signal from the pressure release device.

f. The casing has serious cracks, damage and discharge.

6.2 Operation of the circuit breaker

6.2.1 Observe whether the opening and closing positions are correct, and whether the mechanism operates normally, and make records.

6.2.2 Observe whether there are abnormal noises, severe fever and other abnormal phenomena inside the circuit breaker. If a problem is found, the cause must be found out. If necessary, the dispatcher should be requested to withdraw from operation in time for inspection and maintenance.

6.2.3 The mechanism box of the circuit breaker in operation shall not be opened without authorization, and the power-off opportunity shall be used for cleaning, inspection and defect treatment, and all maintenance items shall be recorded in relevant records.

6.2.4 After the electric energy storage mechanism completes one energy storage, the energy storage switch is turned off. This energy storage is only used for this closing, and the energy storage will be carried out before the next closing. When a power failure requires inspection and test closing, manual energy storage can be used.

6.3 Operation of the isolating switch

6.3.1 Observe whether the isolating switch supporting porcelain bottle is clean, complete, free of cracks, damage, and discharge traces.

6.3.2 Observe whether the mechanical interlocking device is complete and reliable.

6.3.3 Check that there is no overheating, no discoloration, no oxidation, no breakage and other phenomena in the connection of each lead wire.

6.3.4 When the isolating switch is stuck, do not use strong pull to avoid damage to the isolating switch or damage the grounding interlocking device.