Selection Guide and Installation & Maintenance Key Points for Compact Substations

Whether the selection of a compact substation is reasonable and whether the installation is standard directly affect power supply reliability and equipment service life. This article provides a complete operational guide from capacity selection, equipment configuration, foundation construction to operation and maintenance.

I. Capacity Selection Method

Transformer Capacity Calculation

The capacity selection of a compact substation takes the transformer capacity as the core parameter. The calculation steps are as follows:

1. Calculate the total calculated load (kW) within the power supply area
2. Apply a diversity factor (0.7~0.9, depending on load nature)
3. Convert to apparent power: S = P_total / (power factor × transformer load factor)
4. Select the standard capacity level: 50, 100, 160, 200, 250, 315, 400, 500, 630, 800, 1000, 1250, 1600, 2000, 2500kVA
5. Reserve 20%~30% margin for future expansion

Calculation Example

For a residential community with total calculated load of 480kW, power factor 0.9, diversity factor 0.8, and transformer load factor 0.75:

S = 480×0.8 / (0.9×0.75) ≈ 569kVA → Select 630kVA compact substation

II. Transformer Type Selection

III. Foundation Construction Requirements

• The foundation platform is poured with concrete, with a level and flat surface
• The foundation should be at least 300mm above the surrounding ground to prevent rainwater backflow
• The foundation size should be larger than the compact substation base, leaving at least 200mm on each side
• Embed cable inlet and outlet steel conduits, with diameters meeting cable bending radius requirements
• The gap between the base and foundation should be sealed with cement mortar

IV. Earthing System

• Buried ring earthing electrodes around the foundation; burial depth not less than 0.8m
• Transformer working earthing and lightning protection earthing can share the same earthing system
• At least 2 earthing conductors should be led from the earthing electrode to the compact substation foundation platform
• Earthing resistance value ≤4Ω; if soil resistivity is high, add resistance-reducing agents or increase the number of electrodes
• The metal enclosure of the compact substation and high/low-voltage cabinets should all be reliably earthed

V. Pre-commissioning Inspection

• Doors open and close flexibly, with intact sealing strips
• Operating mechanisms are flexible, and electrical interlock functions are normal
• Main switchgear opening and closing operations are normal
• Instruments and relay protection operate accurately
• Busbar connections are tight, and insulation supports are intact
• Fuse ratings are correct, and settings match the design

VI. Operation and Maintenance Key Points

Routine Inspection

• Check the enclosure sealing for signs of water ingress
• Observe transformer operating temperature; temperature control devices should be normal
• Check whether high- and low-voltage side instrument indications are normal
• Listen to transformer operating sound (uniform "humming" is normal)
• Check that enclosure ventilation openings are unobstructed

Periodic Maintenance

• Conduct preventive tests on surge arresters before the annual thunderstorm season
• For oil-immersed transformers, perform simplified insulating oil tests every 3 years
• Clean enclosure ventilation openings and heat sinks quarterly
• Check tightness of all connection bolts and earthing conductors every six months
• After multiple opening/closing operations of low-voltage circuit breakers, check contact wear

Post-Severe-Weather Handling

After severe weather such as strong winds, heavy rain, or snow/ice, increase inspection frequency. Check for damage or deformation of the enclosure, water ingress, foundation settlement, etc. If abnormalities are found, address them promptly.