A box-type substation (also known as a prefabricated substation or package substation) is a compact, factory-assembled power distribution system that integrates:
- High-voltage switchgear
- Distribution transformer
- Low-voltage distribution equipment
These components are arranged according to a predefined wiring scheme and enclosed within a fully sealed steel structure enclosure suitable for indoor or outdoor use.
A box-type substation combines high-voltage power reception, voltage transformation, and low-voltage power distribution into a single unit. The enclosure is designed to be moisture-proof, rust-proof, dust-proof, rodent-proof, fire-resistant, theft-resistant, thermally insulated, and fully enclosed, with optional mobility.
Compared with traditional civil-built substations, box-type substations feature compact structure, fast installation, and fully enclosed operation, making them a modern solution widely used in urban power distribution network construction and renovation.
Application Areas of Box-Type Substations
Box-type substations are widely used in:
- Mines
- Industrial plants and factories
- Oil and gas fields
- Wind power and renewable energy stations
They replace traditional masonry-built distribution rooms and substations, becoming a new-generation integrated power distribution solution.
Typical applications include:
- Residential communities
- Urban public substations
- Commercial districts
- Construction site power supply
Typical Installation Scenarios
1. Street Lighting Power Supply
Both European-type and American-type box substations offer significant advantages over traditional substations for small-load street lighting systems.
They feature:
- Lower construction cost
- Attractive appearance
- Optional landscape-style enclosures (especially European-type box substations)
2. Parks and Residential Communities
In parks and residential areas, power equipment must be aesthetic and space-saving.
Box-type substations:
- Occupy minimal space
- Offer clean and modern appearance
- Blend well with the surrounding environment
3. Industrial and Mining Applications
Factories and mines often face:
- Complex terrain
- High time and construction costs
Box-type substations are ideal due to:
- Easy installation
- Minimal on-site civil work
- High protection level (typically IP33)
- Reduced construction time and labor costs
4. Temporary Power Supply
Construction sites frequently relocate, requiring movable and reliable power distribution equipment.
Box-type substations provide:
- Excellent mobility
- Sufficient load capacity
- Reliable solution for temporary power needs
Configuration of Box-Type Substations
1. High-Voltage Side Configuration
- According to the primary wiring method, box substations are divided into:
- Terminal type (single incoming line, no loop)
- Ring main unit (RMU) type (multiple incoming/outgoing lines, such as one-in-two-out or two-in-one-out)
- On the high-voltage side of European-type box substations, protection may use:
- Circuit breakers, or
- Load switch + fuse combination
For substations with capacity ≤ 800 kVA and lower protection requirements, the load switch–fuse combination is commonly used to reduce cost.
- The high-voltage load switches commonly used in European-type box substations are FLN-12 SF₆ load switches.
2. Automatic Reactive Power Compensation
According to current standards, reactive power compensation capacity is typically configured at 30% of transformer capacity.
However, with the widespread use of inductive loads such as:
- Air conditioners
- Washing machines
- Refrigerators
- Energy-saving lamps
A compensation ratio of 40%–60% of transformer capacity, divided into 10 automatic control steps, is recommended.
Although this slightly increases cost, the improvement in power factor and energy efficiency is significant.
3. Low-Voltage Outgoing Feeder Configuration
The number of low-voltage outgoing feeders is determined based on:
- Load distribution in the supply area
- Reserved spare circuits (typically 1–3 spare feeders)
Circuit breaker ratings are selected according to calculated load current.
Proper configuration requires accurate knowledge of each feeder’s load to ensure safe and reliable operation.
Outdoor Installation Considerations
- Grounding conductors must be copper, with a cross-sectional area not less than 30 mm² to ensure lightning protection reliability.
- The grounding grid should have sufficient coverage and depth, preferably buried at least 1 meter underground, with vertical grounding electrodes added to reduce resistance.
- Installation locations should avoid strong vibration, impact, and electromagnetic interference, while maintaining safe cable entry distances.
- Install the substation on a dry, well-ventilated, level surface, with inclination not exceeding 5°.
- Avoid areas with explosive materials or corrosive gases and liquids.
- Box-type substations require no on-site personnel, resulting in low operating costs and minimal land occupation.
Common Electrical Faults and Solutions
1. Overheating
Prolonged overheating may cause:
- Insulation aging
- Loose connections
- Short circuits or fire risks
Solutions include:
- Regular internal cleaning
- Continuous temperature monitoring
- Early warning systems for abnormal temperature rise
2. On-Load Tap Changer (OLTC) Faults
OLTC faults are rare but may occur due to:
- Long-term mechanical wear
- Insufficient component strength
- Poor manufacturing quality
Strict quality control during production and installation is essential to ensure reliability.
3. Low-Voltage Switch Tripping
Common causes include:
- Busbar faults
- False tripping or protection misoperation
When tripping occurs:
- Inspect transformer low-voltage side protection
- Check for overload, short circuit, or line faults
- Verify protection settings and wiring integrity
Tripping Fault Inspection Procedures
- Transformer tripping may occur at:
- Main transformer breaker
- Line breakers
Root causes are identified through monitoring data analysis.
- Maintenance personnel should:
- Arrive on-site promptly
- Inspect for visible damage
- Check breakers, arc suppression coils, and energy storage mechanisms
- For low-voltage side tripping:
- Check transformer protection first
- Then inspect outgoing feeders and cables
- Restore operation only after eliminating the fault
Fire and Explosion Prevention Measures
- Avoid long-term overload operation, especially in aging equipment.
- For oil-immersed transformers, regularly test transformer oil insulation performance.
- Monitor transformer temperature continuously to prevent core overheating.
- Ensure good conductor contact and promptly repair loose connections.
- Surge arresters must be installed on HV switchgear, transformers, and LV panels to protect against lightning.
- Adequate ventilation and exhaust fans should be included in the design, with automatic temperature monitoring systems for effective heat control.
Conclusion
Box-type substations are typically installed outdoors and operate unattended year-round, requiring only periodic inspections.
Maintenance work involves high risk and complexity, especially during energized inspections.
To ensure safe and stable operation:
- Regular maintenance is essential
- Safety training for operation and maintenance personnel must be strengthened
Proper maintenance and management are key to long-term reliable operation of box-type substations.