As demand accelerates across renewable energy projects, data centers, and distributed power systems, containerized prefabricated substations have evolved from a niche solution into a mainstream infrastructure choice. Within these compact, factory-integrated enclosures, medium- and low-voltage switchgear plays a pivotal role. Space is unforgiving. Efficiency is non-negotiable.

Traditional standard-depth switchgear cabinets impose severe constraints. Large container sizes become unavoidable, and rear-access installation and maintenance demand additional clearance that containerized environments simply cannot provide. On-site assembly further compounds the problem, consuming time, labor, and logistical resources. For this reason, switchgear that supports full front access for installation, operation, and maintenance has become essential.

Design Constraints in Containerized Applications

Containerized switchgear systems are generally tolerant of cabinet width, yet extremely sensitive to depth.
Typical design targets are clear:

• Medium voltage cabinets: ≤ 1200 mm depth

• Low voltage cabinets: ≤ 600–800 mm depth

To achieve this, side-mounted cable connection cabinets are commonly employed. This strategy shifts cable termination laterally, allowing the main functional cabinet to remain shallow. Any increase in overall width is partially offset through vertical, multi-layer internal arrangements, preserving the compact footprint required for container deployment.

Medium-Voltage Switchgear Configuration

Cabinet Architecture

A typical medium-voltage switchgear unit adopts a 1000 mm wide compartmentalized structure, consisting of:

• Left functional compartment (550 mm): circuit breaker and primary operating components

• Right cable compartment (450 mm): current transformers, surge arresters, grounding switches, and cable accessories

Overall dimensions are optimized for container use, with a cabinet depth of approximately 1300 mm and a height of 2300 mm.

Dual-Layer Circuit Breaker Design

A dual-level arrangement—middle-mounted and lower-mounted circuit breakers—enhances operational ergonomics and serviceability. Each breaker compartment is equipped with:

• Metal shutters

• Precision guide rails

• Primary and secondary disconnect contacts

• Reinforced insulation systems

When the circuit breaker is withdrawn, the compartment remains electrically secure. Safety is preserved. Risk is minimized.

Instrumentation and Cable Management

A dedicated instrumentation compartment is positioned at the upper front of the cabinet. Visibility is excellent. Debugging and inspection are straightforward. Terminal blocks may be installed adjacent to the breaker compartment, while operating mechanisms and auxiliary controls can be mounted in the upper section of the cable compartment, benefiting from generous internal volume.

The independent cable compartment accommodates current transformers, cable terminations, surge protection devices, grounding switches, and zero-sequence transformers. Through-core current transformers are used as standard, mounted directly on contact boxes or cable bushings. They allow flexible selection of ratios and protection classes, including PX-class CTs.

Unlike epoxy post CTs—which struggle to satisfy 31.5 kA for 1 s and 80 kA peak dynamic thermal withstand requirements—through-core CTs remain unaffected by short-circuit forces, insulation constraints, or small-current ratio limitations.

Mechanical interlocking ensures that cable compartment doors can only be opened when the corresponding grounding switch is closed. Infrared observation windows further enable real-time inspection of cable terminations and temperature rise without exposure.

Modular, Front-Accessible Maintenance

Reduced cabinet depth makes the design ideal for containerized substations. The modular framework allows flexible configuration changes. Circuit breaker compartments can be withdrawn entirely from the front, simplifying replacement and minimizing downtime.

All installation, wiring, operation, and maintenance activities are performed exclusively from the cabinet front.
Busbars connect at the cabinet top or upper cable compartment. Power cables, secondary wiring, and grounding conductors are all front-accessible. This is true front-operation design, executed without compromise.

For even higher space efficiency, three-layer circuit breaker switchgear configurations are available, enabling dense functional integration while retaining front-access cable compartments—an optimal solution for high-capacity container installations.

Low-Voltage Switchgear Configuration

Low-voltage switchgear adopts a similar philosophy. Side-mounted cable cabinets are used for cable termination, while the main busbar system is located at the rear, simplifying on-site busbar splicing.

The left-side functional compartment can accommodate up to four air circuit breakers, maximizing power density. For molded case circuit breaker (MCCB) feeders, horizontal mounting is employed. Installation density is high. Cable connections are routed laterally, enabling complete front-access maintenance and replacement.

This architecture is particularly effective in containerized environments where accessibility, safety, and service speed directly impact system availability.

Copper Busbar Considerations

The increase in cabinet width necessitates extended feeder busbars routed toward the side cable compartment. As a result, copper consumption rises significantly—often exceeding 1.5 times that of conventional switchgear designs. This trade-off is deliberate. It buys accessibility, modularity, and operational efficiency in constrained prefabricated substations.

Conclusion

Medium- and low-voltage switchgear designed specifically for prefabricated container substations is defined by shallow depth, full front access, modular construction, and mechanical robustness. It responds to the realities of modern energy infrastructure—compact spaces, rapid deployment, and relentless uptime requirements.

In these systems, every millimeter matters. Every design choice serves a purpose.