Underground Box Transformer

With the acceleration of urban and rural modernization, the requirements for power equipment in urban planning, highways, and public facilities construction are increasing. A pre-installed underground box transformer that meets the needs of these fields has emerged and will become a trend in the renovation of urban distribution network equipment in our country. This trend is clearly reflected in the widespread use of such equipment in many developed countries in Europe, America, and Japan. The company independently developed the pre-installed underground box transformer, mainly composed of an underground transformer and an outdoor switch device in the form of an advertising light box. The underground transformer is a new type of compact substation equipment that combines a transformer, high-voltage load switch, fuse, and other components. It is installed in a pit, does not occupy surface space, and can operate submerged in water for a period of time. The outdoor switch device in the form of an advertising light box integrates an advertising board and outdoor switch equipment into a hybrid structure installed on the ground. Inside the box is an outdoor high and low voltage distribution cabinet, with advertising light boxes on both sides, providing excellent visual effects. The underground box transformer aligns with urban ecological design concepts, occupies a small footprint, beautifies the environment, and is suitable for urban main roads, residential communities, airports, stations, highways, and other locations. It will become a trend in urban distribution network equipment renovation. Compared with traditional box transformers, the underground box transformer has the following significant advantages:

1. High Reliability

The underground transformer box shell is made of corrosion-resistant stainless steel and is fully sealed. The high and low voltage input and output lines use waterproof, fully sealed, fully insulated, and fully shielded wiring methods. This ensures the corrosion resistance and sealing capability of the underground transformer, with an overall protection level of IP68, allowing it to operate submerged in water.

The high voltage configuration includes plug-in and standby fuses, which can quickly cut off in case of transformer faults without affecting the overall circuit.

The design and construction of the transformer pit foundation consider waterproofing and drainage. The top ventilation holes have effective rain and waterproof functions, and the sides and bottom are treated with special waterproof materials to prevent water infiltration. A submersible pump controlled by an automatic drainage system is installed at the bottom.

The underground box transformer can operate submerged in water and resist flood disasters. All measures ensure a 20-year service life for the underground transformer, requiring no maintenance or inspection, effectively improving the reliability of the power supply system.

2. Energy Saving and Consumption Reduction

Energy saving and consumption reduction have become a consensus in society. The underground transformer used in the underground box transformer is a low-loss product. The silicon steel sheet core underground transformer reaches the S11 series, with no-load loss reduced by 30% and load loss reduced by 15% compared to ordinary transformers. The underground transformer with an amorphous alloy core has an even greater reduction in loss, with no-load loss decreased by 8%.

3. Noise Reduction

It is well known that the main factor affecting residents around box-type substations is the noise from the transformer. The noise source mainly comes from the core. Transformers installed in ordinary box transformers are generally about 1.2 meters above the ground. If the box transformer is installed close to residents' windows, its noise inevitably enters residents' rooms at night, affecting their sleep. However, once the transformer is installed underground, the noise can be significantly reduced, almost eliminating the impact on residents.

4. Aesthetic and Environmental Coordination

Ordinary box transformers occupy a large area and are difficult to coordinate well with the environment. Especially in some high-end residential communities, distribution facilities or box-type substations scattered in the community cannot coordinate with the environment, affecting the overall aesthetics of the community and even impacting the property prices of nearby buildings.

The underground box transformer, with the transformer installed underground, does not affect the surrounding environment. The distribution box installed on the ground is small and easily coordinates with the surrounding environment. In residential communities, the ground distribution box can be integrated with community landscaping, becoming part of the scenery. On urban main roads and highways, the ground distribution box can be designed as an advertising light box.

5. Creating Value for Customers

The underground box transformer occupies a small area and can replace traditional distribution rooms in residential communities, reducing the construction of distribution rooms and providing significant investment benefits.

The underground box transformer has an attractive appearance and coordinates with the surrounding environment. Installed in residential communities, it not only does not affect the property prices of nearby buildings but also enhances the community's quality.

The underground box transformer installed on urban main roads and highways features advertising light box-style switch equipment on the ground. Large advertising light boxes will bring long-term advertising revenue to customers.

Model Description

Operating Environment

● Altitude: Not exceeding 1000m.

● Ambient Temperature: Maximum temperature: +40°C; Minimum temperature: -25°C.

● Relative Humidity: Daily average not exceeding 95%; monthly average not exceeding 90%.

● Installation tilt not exceeding 3 degrees, no frequent severe vibration or impact.

● Surrounding air should be free of explosive, corrosive, or flammable gases and other obvious pollutants.

Technical Parameters

● Main technical parameters and performance of the underground transformer.

1. Model and specifications: ZGS11-Z(H)·D-30~1000/10; ZGSH15-Z(H)·D-30~1000/10.

2. Rated voltage: High voltage 10kV, low voltage 0.4kV.

3. Capacity range: 30~1000kVA.

4. Frequency: 50Hz; 5. Phases: Three-phase.

6. Connection group designation: Dyn11.

7. Short-circuit impedance voltage: 4%-4.5%.

8. Insulation level: Primary side power frequency withstand voltage: 35kV; primary side impulse withstand voltage: 75kV; secondary side power frequency withstand voltage: 5kV.

9. Losses: Meets national standard S11 series (silicon steel sheet core); meets national standard S15 series (amorphous alloy core).

10. Shell protection level: IP68.

11. Noise level: Less than or equal to 50dB.

12. Usage environment: basement or pit

13. High-voltage continuous parts: imported plug-in sealed elbow; low-voltage connectors: US 3M waterproof sealing material

14. Box structure: the box shell is integral and made of corrosion-resistant stainless steel

● Main technical parameters of prefabricated pit

1. The pit is formed by pouring reinforced concrete columns with thickness ≥150mm.

2. The pit cover is made of precast cement slabs and is equipped with an openable inspection hole.

● Main technical parameters of high-voltage switchgear

1. Rated voltage: 12kV

2. Rated frequency: 50Hz

3. Rated current: 630A

4. Rated short-time withstand current: 20kA/2s

5. Rated peak withstand current: 50kV

6. Rated short-circuit making current: 50kV

7. Rated power frequency withstand voltage (phase to ground/open gap): 42/48kV (1min)

8. Rated lightning impulse withstand voltage (phase to ground/open gap): 75/85kV

9. Protection level: IP34

● Main technical parameters of low-voltage switchgear

1. Rated voltage: 400V

2. Rated frequency: 50Hz

3. Main circuit rated current: 100A~200A

4. Rated short-time withstand current: 15kA, 30kA

5. Rated peak withstand current: 30kA, 63kA

6. Protection level: IP34

Underground combined transformer

● The box is made of stainless steel, fully sealed, with a protection level of IP68, capable of operating submerged in water;

● High and low voltage incoming and outgoing lines use waterproof, fully sealed, fully insulated, and fully shielded wiring methods for safer operation;

● Uses naphthenic transformer oil to ensure good heat dissipation capability;

● Uses amorphous alloy core for significant energy-saving effects;

● High insulation heat resistance level, environmentally friendly;

● Backup and plug-in fuses provide safer protection for the transformer;

● Load switches have two, three, and four position types, suitable for various power supply systems.

Prefabricated pit foundation

● Pit foundation: can use steel plates thicker than 6mm pre-pressed and formed, fully sealed structure to ensure surface water and other debris cannot enter the pit; can also use prefabricated reinforced concrete structure with advanced waterproof technology to ensure no leakage.

● The bottom of the pit is equipped with a water collection pool and a submersible pump controlled by an automatic drainage system.

● High and low voltage cable support brackets are installed inside the pit for convenient cable installation and fixing.

● Waterproof lighting is installed inside the pit for easy maintenance.

● The foundation top cover is equipped with an openable inspection hole.

Outdoor switchgear with advertising light box design

● The protective shell of the switchgear adopts an advertising light box structure; the two doors of the light box shell can open fully and are supported by gas springs for positioning, facilitating operation and maintenance of the switchgear;

● The light box is equipped with an insulation layer with good heat insulation effect;

● Both sides of the light box shell are advertising panels using compact, uniformly lit LED light sources;

● The advertising light box and the switchgear door locks are independently set, so maintenance of the light box does not affect the operation of the switchgear;

● The light box shell has no audible or visual alarm device; if damaged externally, it can trigger an alarm signal;

● The switchgear uses a double-door structure with a protection level of IP34; the second door is an instrument door, ensuring that after the light box shell is damaged, the low-voltage cabinet still maintains a complete and independent outdoor low-voltage product protection level;

● Fans hidden in the light box shell can automatically ventilate and supply air inside the pit foundation to reduce temperature.