| Voltage and network role | Identify whether the site serves transmission, sub-transmission, distribution, or a customer facility. | Common sub-transmission and distribution levels include 11, 13.8, 22, 33, and 69 kV; transmission levels vary by country and grid. | Confirm the utility’s standard nominal voltages, insulation levels, and connection requirements before selecting equipment. |
| Load and transformer capacity | Estimate peak demand, load growth, power factor, contingency needs, and the consequences of losing one transformer. | Transformer ratings are selected to suit the network and are available in a wide range; there is no universal capacity that defines a distribution or transmission substation. | Model normal and contingency conditions. Check whether the design can maintain required service after the loss of a major component. |
| Capital cost | Compare land, civil works, transformers, switchgear, protection and control, interconnection, and commissioning costs. | Costs are highly site- and scope-specific. Brownfield upgrades, remote locations, difficult ground conditions, and major transmission connections can materially increase project cost. | Request comparable, scope-based estimates and include owner’s costs, contingencies, taxes, escalation, and decommissioning where applicable. |
| AIS versus GIS layout | Compare air-insulated switchgear (AIS) and gas-insulated switchgear (GIS) for space, environment, access, and maintenance. | AIS generally needs more clearance and land. GIS can reduce the switchyard footprint but may have higher equipment cost and specialized maintenance needs. | Evaluate total life-cycle cost, site constraints, outage access, and applicable rules for insulating gases—not just initial equipment price. |
| Reliability and redundancy | Review bus configuration, breaker arrangement, transformer redundancy, protection coordination, and restoration plans. | A single-bus arrangement is generally simpler; sectionalized, ring-bus, or breaker-and-a-half arrangements can provide more operating flexibility but add equipment and complexity. | Choose the arrangement based on required reliability, fault exposure, switching practices, and the cost of interrupted service. |
| Expansion potential | Check space for future bays, transformers, cable routes, access roads, and control-room equipment. | Future expansion can be constrained by property boundaries, easements, clearances, environmental buffers, and the arrangement of existing equipment. | Reserve land and establish a staged single-line diagram early; verify that initial construction will not block planned additions. |
| Permitting and land use | Assess zoning, planning approval, environmental review, noise, drainage, visual effects, and community consultation. | Requirements depend on the country, state or province, local authority, project type, and whether new transmission lines or other facilities are included. | Engage relevant authorities and the connecting utility during site screening; permitting and land acquisition can affect both schedule and cost. |
| Electrical and safety standards | Verify design requirements for insulation coordination, grounding, short-circuit duty, clearances, arc-flash risk, and equipment testing. | Potential references include IEC 61936-1 for power installations above 1 kV AC, IEC 62271 series for high-voltage switchgear, IEEE Std 80 for substation grounding, and locally adopted electrical codes. | Confirm which standards and editions are adopted by the authority having jurisdiction and the utility; standards do not replace local code requirements. |
| Grid connection and compliance | Determine interconnection studies, protection settings, metering, communications, and operating requirements. | In the United States, applicable requirements may include FERC-jurisdictional rules, NERC reliability standards where applicable, and regional or utility interconnection requirements. | Establish the responsible grid operator and applicable compliance framework at project start; requirements differ across jurisdictions and project types. |
| Environmental and climate resilience | Review flood, wildfire, seismic, wind, icing, heat, contamination, and oil-containment risks. | Site-specific hazard maps and engineering studies should inform design elevations, drainage, equipment ratings, fire protection, and spill-control measures. | Select a site and equipment ratings that account for current hazards and expected service life, then document mitigation and emergency plans. |
| Operations and life-cycle cost | Compare inspection, maintenance, spare-parts, outage, staffing, and replacement requirements. | Life-cycle cost depends on equipment design, duty, environment, labor, and outage constraints; purchase price alone does not capture operating cost. | Evaluate the full life-cycle cost and ensure maintainers can access equipment safely without unacceptable service interruptions. |