The first consideration is insulation; an insulation scheme must be formulated to determine the specific method to be employed—whether it be air insulation, gas insulation, solid insulation, or a composite air-solid system. If a purely air-insulated system is selected, it must strictly adhere to the relevant standards regarding air clearance distances.

This point is unequivocal: for electric fields exhibiting even slight non-uniformity, the required air clearance—whether between live conductors or between a conductor and ground—is determined by the specified lightning impulse withstand voltage. Both IEC and domestic standards (such as GB/DL) provide clear definitions in this regard. Failure to meet this minimum air clearance renders it impossible to pass the lightning impulse withstand voltage test; conversely, if this requirement is met, there is a greater than 99% probability of successfully passing the lightning impulse test. Indeed, if the design clearance exceeds the minimum distance mandated by the standard, the product is deemed to satisfy the corresponding lightning impulse withstand voltage requirement by design—meaning that no actual physical testing is required. For instance, consider an IEC voltage class of 17.5 kV with a specified lightning impulse withstand voltage of 95 kV; if air insulation is utilized, the required clearance must be ≥ 160 mm. In contrast, domestic GB standards for 12 kV switchgear require a minimum clearance of only ≥ 125 mm; consequently, such a design cannot pass the 95 kV lightning impulse withstand voltage test and is therefore unsuitable for use in 17.5 kV systems.

Similarly, the adoption of other insulation methods necessitates adherence to their respective design standards; during the design phase, the distances between all critical points must be measured to ensure they exceed the minimum requirements stipulated by the standards.

Based on the component sequence defined in the primary system schematic, the various components are arranged within the switchgear according to their specific insulation clearance requirements. The typical layout sequence is as follows: Main Busbar → Upper Branch Busbar → Contact Box → Circuit Breaker → Contact Box → Current Transformer → Earthing Switch → Outgoing Cable Connection Busbar → Voltage Transformer.

Regarding equipment temperature rise: the switchgear design must account for the temperature rise resulting from the heat generated by current flow. Particular attention must be paid to high-heat-generating components—such as the vacuum interrupters and their upper/lower connection terminals within a vacuum circuit breaker, or the primary moving and stationary contacts of a withdrawable circuit breaker. In these critical areas, airflow must be carefully considered to prevent heat accumulation and ensure effective dissipation. Generally, current transformers may be positioned at a greater distance from the contact boxes to facilitate the conduction of heat—generated at the connection points between the busbars and the moving/stationary contacts—away from the sensitive transformer components. Furthermore, the circuit breaker compartment must incorporate appropriate ventilation designs at both its bottom and top sections.

Finally, regarding the dynamic and thermal stability of the busbars: the spacing between busbar insulation supports must be calculated based on the equipment's specified peak withstand current. The structural support requirements for the main busbar—in particular—must be carefully evaluated. These parameters are determined by applying the relevant calculation formulas to establish the fundamental design principles. For instance, in a configuration rated at 31.5 kA / 80 kA with a phase spacing of 210 mm, the support spacing must not exceed 1 meter.

Regarding considerations for internal arc pressure relief: the shockwave generated by an internal arc explosion must be capable of dislodging the pressure-relief cover plates. Consequently, it is essential to ensure that the pressure-relief channels remain unobstructed; this facilitates a rapid response—minimizing the time required for the covers to open—and ensures the swift release of internal pressure.

In terms of ease of installation and maintenance—particularly for non-standard projects—clients may request configurations involving multiple windings. Such requirements necessitate the use of multiple epoxy-cast pillar-type current transformers; furthermore, certain applications may require the incorporation of window-type current transformers to satisfy PX-class protection standards, all while maintaining the capability for operational control and maintenance to be performed from the front of the switchgear cabinet.