Box-type Substation Cabinet Structure
The cabinet of American-style box-type substations adopts anti-corrosion design and special painting treatment, which can be applied to various harsh environments, such as areas with frequent rainstorms and high pollution.Before painting, the cabinet undergoes eight pre-treatment processes, followed by seven painting and baking processes, showing its prudent attitude towards anti-corrosion.However, the enclosure of American-style box-type substations produced in China is hardly specially treated, basically adopting electrostatic spraying after pickling, and even some enterprises do not carry out pickling treatment. What's more, only painting treatment is carried out on the outer surface. It is conceivable how the anti-corrosion capacity of its enclosure is.Even for electrostatic spraying treatment, some dead corners often appear during the bottom surface treatment, and it is difficult for electrostatic spraying to spray powder on these poorly treated parts, so hidden dangers of rust are inevitably left.Since the box-type substation has to work outdoors exposed to wind, rain, and sunlight for years, if the surface treatment is not good, rust will be very serious.This problem is very important and has been a topic of great concern, attention, and research in China for decades, so many manufacturers adopt some other technologies to solve this problem.Regarding the protection issue, the transformer oil tank and radiator parts of the American-style box-type substation are exposed outside, whose purpose is to improve the heat dissipation conditions. However, due to its direct exposure to sunlight, whether it will affect the temperature rise under the thermal radiation of sunlight has not been introduced in detail.In addition, the exposed parts are vulnerable to damage from external collision and knocking. Once damaged, a large amount of transformer oil will be lost, with unimaginable consequences. Therefore, some domestic manufacturers wrap a layer of steel plate around the radiator to increase the protection capacity.
High-voltage Load Switch of American-style Box-type Substation
The load switch of the American-style box-type substation is placed in the transformer oil tank. The oil-immersed three-phase linkage switch can be divided into two types: two-position (terminal type) and four-position (ring network type).Since this load switch is placed in the transformer oil tank, its closing position can only be judged according to the indication of the external operation panel, and its operation must be carried out through a special insulating operating rod, so its operation is relatively complex.From this point of view, its operation is very inconvenient. In addition, since the open contacts (i.e., obvious break points) of the load switch cannot be seen, people will feel uneasy after opening. In addition, once the load switch fails, replacement and maintenance will be very difficult. The load switch generally adopts a vacuum circuit breaker.
Maintenance of American-style Box-type Substation
After installation and use, the American-style box-type substation basically requires no maintenance, but due to various reasons, the maintenance work of the products produced in China is indispensable.
- Due to the surface treatment technology of the enclosure, it is necessary to strengthen the inspection of its rust condition.
- The oil filled in the oil tank of American-style box-type substations is generally FR3 insulating oil, whose ignition point can reach 312℃, and it has excellent electrothermal characteristics, high insulation strength, good lubricity, strong arc-extinguishing ability, non-toxicity, and biodegradability, thus minimizing harm to the environment and health.FR3 insulating oil does not form precipitates like traditional mineral oil, but most of the American-style box-type substations produced in China are filled with 25# ordinary mineral oil. In addition, under normal circumstances, the upper part of the oil tank of American-style box-type substations is filled with inert gas to prevent moisture in the air from exchanging into the oil.However, it is possible that no domestic enterprise has carried out this work for American-style box-type substations produced in China. Over time, the performance of the oil will decrease. In addition, its sealing performance cannot meet the requirement of 7 Psig, so regular oil change is necessary.
- The American-style box-type substation has no oil temperature protection, only a thermometer to display the oil temperature. When the oil temperature is too high, the plug-in fuse is used for protection, and there is also a pressure relief valve to release excessive pressure in the oil tank.Therefore, it is necessary to frequently check whether the fuse operates normally under these two conditions and whether the enclosure has oil leakage.
- Since the oil tank of the American-style box-type substation is exposed outside, regular inspections should be carried out to prevent damage and oil leakage caused by external collision.
Domestic Box-type Substation
Compared with the American-style box-type substation, the domestic box-type substation adds an earthing switch and an arrester, and there is a mechanical interlock between the earthing switch and the main switch, which can ensure absolute personal safety during the maintenance of the box-type substation.The domestic box-type substation uses one fuse per phase instead of two fuses of the American-style box-type substation for protection. Its biggest feature is that when any phase fuse blows, it will ensure that the load switch trips and cuts off the power supply, and the main switch can only be closed after replacing the fuse, which is not available in the American-style box-type substation.
The domestic box-type substation generally adopts a structure where each unit is independent of each other, with a transformer room, a high-voltage switch room, and a low-voltage switch room respectively, which are connected into a complete power supply system through wires.
The transformer room is generally placed at the back. To facilitate user maintenance, replacement, and capacity expansion, the transformer can be easily pulled out of the cabinet or lifted out from the top.Since the transformer is placed in the enclosure, the advantage is that it can prevent the temperature rise caused by direct sunlight on the transformer, and also effectively prevent external collision, impact, and electric shock accidents caused by touch. The disadvantage is that it puts forward higher requirements for the heat dissipation of the transformer.The high-voltage switch room is equipped with an independently enclosed high-voltage switch cabinet. The cabinet is generally equipped with a gas-generating, compressed-air, or vacuum load switch-fuse combination electrical appliance. The high-voltage fuse installed on it can ensure that the main switch trips when any phase fuse blows to avoid phase-loss operation.In addition, it is also equipped with an earthing switch, which is interlocked with the main switch, that is, the earthing switch can only be closed after opening the main switch, and the main switch cannot be closed after closing the earthing switch, so as to ensure safety during maintenance.The cabinet is also equipped with a high-voltage arrester, and the operation of the entire switch is very convenient. All switches can be closed and opened only by using a special matching handle. At the same time, the opening and closing state of the main switch can be observed through the transparent window.
Low-voltage Switch CabinetGenerally, the low-voltage switch cabinet is equipped with a main switch, each distribution branch switch, a low-voltage arrester, instruments for displaying voltage, total current, and branch current.At the same time, to better protect the safe operation of the transformer, measures are often taken to monitor the top oil temperature of the transformer. When the oil temperature reaches a dangerous temperature, it can automatically stop the operation of the low-voltage side (disconnect the low-voltage side load). Of course, its action value can be set according to requirements.
Enclosure and ProtectionEach switch cabinet of the domestic box-type substation is made into an independent cabinet and installed in the enclosure, which can be easily replaced and maintained, and also improves the protection capacity and safety.Its steel plate enclosure is subject to anti-corrosion treatment by special processes, so that its protection capacity can reach more than 20 years. At the same time, the top cover adopts a double-layer structure to reduce the thermal radiation of sunlight. Its appearance can be matched with various colors coordinated with the use environment according to user requirements, so as to achieve the effect of adapting to and embellishing the natural environment.
Other AspectsBoth American-style and domestic box-type substations can add functions such as metering and compensation, but the volume is slightly increased. In addition, the domestic box-type substation can also adopt elbow-type cable heads for incoming cable plugging.Incidentally, the transformers of domestic box-type substations generally adopt S9 fully sealed low-loss transformers, while some foreign products have adopted amorphous alloys as transformer cores to reduce losses.Amorphous alloy transformers have been produced in small batches in China. In other words, the one-time investment is large, but the economic benefits brought by them are quite considerable.
The domestic horizontal box-type substation should be more accurately called the European-American integrated box-type substation. The appearance of the horizontal box-type substation is the same as that of the European-style box-type substation, but its volume is much smaller than that of the European-style box-type substation and slightly larger than that of the American-style box-type substation.This is because the transformer, load switch, and low-voltage outgoing line mode of the horizontal box-type substation are basically the same as those of the American-style box-type substation, but it has an independent transformer room.Since both high-voltage and low-voltage outgoing lines are on the side wall, there is no need to consider guardrails and other facilities in the transformer room.Due to the small volume and compact structural characteristics of the horizontal box-type substation, some designers have greatly simplified the design of its top cover (without adding thermal insulation layers, etc.), only retaining the natural ventilation and heat dissipation cooling operation mode, which greatly reduces the heat dissipation level of the transformer placed in the box-type substation cabinet.
Supplementary Notes
- Terminology Standardization
- Box-type substation: The standard translation in the power equipment industry, also abbreviated as box substation in some cases.
- Load switch-fuse combination electrical appliance: A professional term for high-voltage switchgear, accurately reflecting the combined structure and function of the equipment.
- Amorphous alloy transformer: A new type of energy-saving transformer, the translation conforms to international industry norms.
- Format Adjustment
- The original text has repeated 'box-type substation' multiple times, and the translation has been appropriately simplified according to the context to avoid redundancy while ensuring the accuracy of the meaning.
- For technical parameters such as transformer capacity and fuse types, the original data has been directly retained to meet the requirements of technical document translation.
- Cultural and Technical Background Treatment
- For the differences in metering requirements of power supply departments in different regions of China, the translation uses a narrative tone consistent with the original text to ensure that the information is complete and accurate.
- For special processes such as surface treatment and insulation oil types, professional expressions are adopted to meet the reading habits of the English technical community.
Foshan Chanxingte Transformer Co., Ltd.
Address: No. 8, Zhongyou Avenue, Leping Town, Sanshui District, Foshan City
