A Compact Substation (CSS) is a prefabricated, factory-assembled unit that integrates medium-voltage (MV) switchgear, a distribution transformer, and low-voltage (LV) switchgear into a single, compact enclosure. Designed for rapid deployment and minimal spatial footprint, CSS units are ideal for urban, industrial, and infrastructure applications where space, safety, and reliability are paramount.

 Technical Specifications of a Compact Substation

1. Transformer

• Type: Hermetically sealed oil-immersed or dry-type (cast resin) transformers.
• Power Rating: Upto 2500 kVA.
• Primary Voltage: Up to 33 kV.
• Secondary Voltage: 0.415 kV.
• Vector Group: Usually Dyn11.
• Impedance: Starting from 4.5%, depending on design.

2. Medium Voltage (MV) Switchgear

• Configuration: Ring Main Unit (RMU) or Vacuum Circuit Breaker (VCB) panels.
• Voltage Rating: 12 kV to 24 kV.
• Current Rating: Up to 630 A.
• Short-Circuit Rating: Up to 21 kA for 1 second.
• Insulation: SF6 gas-insulated or air-insulated options.
• Protection: Equipped with numerical relays for overcurrent and earth fault protection.

3. Low Voltage (LV) Switchgear

• Configuration: Air Circuit Breakers (ACB), Molded Case Circuit Breakers (MCCB), or fuse switches.
• Voltage Rating: 415 V.
• Current Rating: Up to 2500 A.
• Features: Includes metering devices, protection relays, and provision for Automatic Power Factor Correction (APFC) panels.

4. Enclosure

• Construction: Fabricated from CRCA or galvanized steel sheets, with thicknesses of 2 mm for load-bearing members and 1.5 mm for non-load-bearing members.
• Protection Class: IP54 for MV and LV compartments; IP23 for the transformer compartment.
• Surface Treatment: Powder-coated with UV-resistant finishes for outdoor durability.
• Compartments: Segregated sections for MV switchgear, transformer, and LV switchgear to enhance safety and ease of maintenance.

5. Standards Compliance

• IEC 62271-202: High-voltage/low-voltage prefabricated substations.
• IEC 60076: Power transformers.
• IEC 60439-1: Low-voltage switchgear and controlgear assemblies.
• IS 14786: Indian standard for prefabricated substations.

6. Additional Features

• Internal Arc Protection: Type-tested for internal arc faults up to 20 kA for 1 second, ensuring personnel safety.
• Cooling: Natural or forced ventilation systems, depending on transformer type and rating.
• Monitoring: Provision for temperature sensors, oil level indicators, and pressure relief devices.
• Earthing: Comprehensive internal earthing system connecting all metallic parts to a common earth point.

 Typical Dimensions and Weight

 Applications

• Urban and Rural Distribution: Ideal for areas with space constraints.
• Industrial Facilities: Provides reliable power distribution for manufacturing units.
• Commercial Complexes: Ensures uninterrupted power supply for malls, offices, and hospitals.
• Renewable Energy Projects: Integrates seamlessly with solar and wind power installations.
• Infrastructure Projects: Suitable for airports, railways, and data centers.