Overview
Urban construction in China is entering a new stage of city beautification and greening aimed at improving the appearance of cities. Pedestrian commercial streets, leisure centers, and boutique districts successively introduced by advanced cities can be said to have approached international standards, and the requirements for the tidiness and landscape of box substation sites are increasingly high.
The pre-installed underground box substation is a product developed under our company's concept of advocating green power and optimizing the urban environment, through learning advanced foreign technologies and integrating modern urban ecological design concepts, gradually installing transformers underground.
Underground transformers, also known as subsurface transformers, are referred to in China as underground composite transformers—compact substation equipment in which transformers, high-voltage load switches, fuses, etc. are placed in an oil tank. They are installed in pits, occupy no surface space, and can operate while submerged in water for a period of time. They are suitable for urban distribution networks such as urban residential communities, industrial parks, and major urban traffic arteries. The use of underground transformers can save the floor space of urban distribution facilities and improve urban land utilization. However, isolated underground transformers do not solve the problem of low-voltage configuration, so their promotion in China has been greatly affected.
With advanced technology, our company has meticulously created a new generation of underground distribution equipment—the pre-installed underground box substation. This product consists of an underground composite transformer, an outdoor low-voltage cabinet, a light-box-type low-voltage protective enclosure, and a prefabricated underground composite transformer foundation. It is a complete set of underground transformer and distribution equipment pre-assembled at the factory. It can also be equipped with a light-box-type cable branch box and light-box-type high-voltage metering according to user requirements, providing a complete solution for 10kV power distribution. The pre-installed underground box substation provides entirely new possible technical equipment for the underground renovation of urban power grids, and offers favorable conditions for power grid renovation in areas with tight land and building space under environmental constraints. It is mainly used to replace traditional civil-construction substations, European-style box substations, and American-style box substations, and is a new type of power product that realizes power installation and distribution functions.
Operating Conditions and Environment
1. Altitude: no more than 1000m;
2. Ambient temperature: maximum temperature: +40℃; minimum temperature: -45℃; maximum monthly average temperature: +30℃; maximum annual average temperature: +20℃;
3. Installation environment: no explosive or corrosive liquids, gases, or dust; the installation site has no severe vibration or impact; operation while partially or fully submerged in water is allowed for a certain period of time;
4. Ground acceleration Ag caused by earthquakes: horizontal direction lower than 3m/s; vertical direction lower than 1.5m/s;
5. Waveform of power supply voltage: approximately sinusoidal;
6. Three-phase power supply symmetry: for three-phase underground transformers, the three-phase power supply voltage should be approximately symmetrical.
Product Features
The underground box substation has the characteristics of corrosion resistance, waterproofness, low temperature rise, low noise, convenient installation, and maintenance-free operation; it is a typical energy-saving product.
The oil tank is made of low-alloy structural steel, which has very good comprehensive mechanical properties, welding performance, and low-temperature toughness. The tank body adopts thermal zinc spraying technology supplemented by plastic spraying treatment, providing strong corrosion resistance.
A fully sealed structure is adopted, and the exposed parts of the high-voltage and low-voltage terminals are isolated from the environment by imported sealing and waterproof materials. During installation, the local underground transformer is placed in a pit. When the pit is flooded or even when the underground transformer is submerged, it can still operate safely. It can withstand flood disasters and effectively improve the reliability of the power supply system.
A unique heat sink structure is adopted, ensuring the heat dissipation capacity and rust resistance of the heat sinks.
The protective enclosure of the low-voltage cabinet adopts a patented outdoor light-box-type protective enclosure. Both sides of the light-box-type enclosure can be equipped with all-weather advertising panels, using small-sized, green, and energy-saving LED light-emitting components.
The underground transformer foundation is a pre-installed structure and can be prefabricated with different materials flexibly according to customer requirements.
Main Technical Parameters
| No. | Name | Unit | High-voltage side | Transformer side | Low-voltage side |
| 1 | Rated voltage | kV | 10 | 1 | 0.4 |
| 2 | Maximum operating voltage | kV | 12 | 1 | |
| 3 | Rated capacity | kVA | 50～1600 | ||
| 4 | Rated current (component) | A | 5～630 | 50～3200 | |
| 5 | Short-time withstand current | kA | 12.5; 16; 2 | 15～75 | |
| 6 | Rated short-circuit duration | S | 2 | 1 | |
| 7 | Peak withstand current | kA | 20/31.5/40 | 30～165 | |
| 8 | Power-frequency withstand voltage | kV | 35 | 75 | 5 |
| 9 | Lightning impulse withstand voltage | kV | 75 | 75 | |
| 10 | Rated breaking current of high-voltage current-limiting fuse | kA | 50 | ≤48 | |
| 11 | Noise level | db | |||
| 12 | Rated frequency | Hz | 50 |
