Box-type Substation Rating Is Decided by Ventilation and Compartment Layout

Box-type Substation Rating Is Decided by Ventilation and Compartment Layout

A box-type substation — package substation in industry usage — delivers the function of a masonry electrical room inside one factory-built enclosure, type-tested as a complete unit. The governing standard is IEC 62271-202 for AC prefabricated substations above 1 kV to 52 kV; China's GB/T 17467-2020 adopts it for the 3.6–40.5 kV class. Two layout philosophies divide the market. European-style construction separates high-voltage switchgear, transformer and low-voltage distribution into distinct compartments — larger footprint, but each function stays isolated for maintenance and testing. American-style construction compacts all three around a sealed immersed transformer whose tank and radiators shed heat directly to ambient, shrinking the enclosure to a fraction of European volume at the same rating. Heat is the silent limit. A transformer inside an undersized ventilation scheme derates: losses accumulate, compartment air heats, and the rated kVA becomes a figure from an open-air test that never happened. IEC 62271-202 requires temperature-rise testing of the complete substation — every loss source heating the same air — and ventilation area must answer that measured total, not a rule of thumb. Before a box-type substation is ordered, fix four names: voltage class and vector group, compartment layout, enclosure protection class, and the whole-unit temperature-rise report. Ventilation settles the real capacity.

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