The Principle of "Three-in-One" Integrated Design for Combined Substations
The "Three-in-One" integrated design refers to the modular integration of three core functional units in combined substations: high-voltage switchgear, power transformers, and low-voltage distribution devices. This design principle aims to achieve compactness, reliability, and efficient space utilization by integrating these units into a unified enclosure or modular system, while ensuring independent operation and maintenance of each unit.
Function: Controls and protects the high-voltage power supply system, including circuit breakers, load switches, and protection relays.
Integration Design: Isolated in a dedicated compartment with anti-arcing and fault isolation features. It connects to the transformer via insulated busbars or cable terminations, adhering to safety clearances (e.g., creepage distance ≥125mm for 10kV systems).
Example: Ring main units (RMUs) with SF6 or vacuum interrupters are pre-installed in the high-voltage compartment, enabling quick switching and fault protection.
Function: Steps down high-voltage power to low voltage (e.g., 10kV/0.4kV), serving as the energy conversion core.
Integration Design: Mounted on a shock-absorbing base within a ventilated compartment. Dry-type transformers (e.g., epoxy resin cast) are preferred for fire safety, while oil-immersed transformers require oil leakage prevention and fireproof partitions.
Technical Focus: Thermal management systems (temperature sensors and fans) are integrated to monitor winding temperatures, ensuring the transformer operates within IEC 60076 standards.
Function: Distributes low-voltage power to loads, including circuit breakers, contactors, and metering devices.
Integration Design: Configured in a separate compartment with busbar systems and modular panels. It connects to the transformer via low-voltage busbars and features flexible outgoing cable terminations.
Smart Integration: Intelligent monitoring units (e.g., PLCs or IoT sensors) are embedded to track parameters like current, voltage, and power factor, enabling remote management.
Modular Enclosure: The three units are housed in a weatherproof shell (e.g., stainless steel or GRP) with IP54/IP65 protection. Compartments are separated by fireproof partitions, while sealed gaskets prevent dust and moisture ingress.
Space Optimization: Compared to traditional separate installations, the "Three-in-One" design reduces floor space by 30–50%, making it suitable for urban areas with limited space.
Busbar System: High-voltage and low-voltage busbars are pre-installed in the factory, with insulated connections to minimize on-site wiring errors. For example, 10kV busbars use heat-shrinkable insulation to meet creepage requirements.
Protection Coordination: Relays in the high-voltage module and circuit breakers in the low-voltage module are coordinated to ensure selective tripping during faults, reducing power outages.
Integrated Ventilation: A unified cooling system (fans and vents) regulates temperature across all compartments, with temperature sensors triggering fans when the transformer winding temperature exceeds 100°C (for dry-type transformers).
Noise Control: Soundproof materials (e.g., mineral wool) are embedded in the enclosure to limit noise below 65dB at 1m, complying with environmental standards.
Urban Power Grids: Suitable for compact substations in commercial districts, where space is limited but reliability is critical.
Industrial Parks: Enables flexible expansion of low-voltage distribution modules as load demands grow, without modifying high-voltage or transformer sections.
Key Considerations:
Load Forecasting: Sizing the transformer and low-voltage panels based on projected loads.
Fault Clearance: Ensuring high-voltage switchgear can interrupt short-circuit currents (e.g., 20kA for 10kV systems).
Maintenance Access: Designing removable panels for each module to facilitate independent servicing (e.g., replacing low-voltage breakers without shutting down the transformer).
While prefabricated substations also integrate components, the "Three-in-One" design of combined substations emphasizes modular flexibility (e.g., replacing only the low-voltage module during upgrades) versus the prefabricated type’s all-in-one rigidity. This makes combined substations more adaptable to complex projects requiring phased expansions or custom configurations.
In summary, the "Three-in-One" principle transforms traditional separate substation components into a cohesive, optimized system, balancing space efficiency, operational reliability, and maintenance flexibility for modern power distribution needs.
