A box-type substation (compact substation) integrates a high-voltage switch, transformer and low-voltage distribution device inside a pre-assembled outdoor enclosure. Compared to conventional masonry substations, compact substations offer a smaller footprint, shorter installation periods and easier transportation — making them widely used in urban distribution networks, industrial parks, renewable energy plants and temporary power applications.
The first step in selection is determining the voltage level and capacity. Typical primary voltages are 10 kV and 35 kV, with a secondary voltage of 0.4 kV. Rated capacity ranges from 50 kVA to 5,000 kVA. Calculate the load and add a 15–20% margin to avoid chronic overloading or light loading, both of which increase losses.
The IP (Ingress Protection) rating is another critical parameter. In industrial parks, coastal areas or dusty environments, IP34 or higher is recommended. For temporary outdoor installations, IP23 is usually adequate. At altitudes above 1,000 m, specify a high-altitude variant to compensate for reduced insulation strength and cooling efficiency.
Loss figures directly affect operating costs. No-load and load losses are the core data for whole-life-cost analysis. Choosing S13, S15 or amorphous-core transformers can reduce losses by 20–70% versus a conventional S11 unit, with significant long-term returns.
Typical scenario reference: Industrial parks generally specify 10 kV or 35 kV dual-branch substations rated 800–2,000 kVA. Photovoltaic plants prefer 35 kV step-up compact substations matched to the inverter output. Urban rail transit requires specialist variants with strict noise and fire-resistance ratings.
Finally, pay attention to system compatibility: protection relay settings, metering arrangement (HV or LV side), communication interfaces (Modbus, IEC 61850) and future maintenance access. SAD (Zhejiang Shidian Complete Electrical Equipment) can provide customised selection solutions for your specific project — visit 21b.cn for more information.