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A dry-type unit has no insulating oil: the windings are vacuum cast in epoxy resin or use non-encapsulated class H insulation, so the transformer is self-extinguishing, cannot leak oil and can sit at the load centre in high-rise buildings, metro stations, airports or shopping centres. An oil-immersed unit uses a fully sealed tank, dissipates heat and handles overload better and costs less for the same rating, which suits outdoor sites, industrial plants and box-type substations. The choice follows the fire requirements, the installation environment and the capacity class; we supply both families.

The American-style unit (ZGS11 compact pad-mounted transformer) puts the HV load-break switch, the fuses and the transformer in one oil-filled tank, which keeps it small and compact and suits urban load centres, housing estates, hospitals, airports and stations. The European-style YBM prefabricated substation holds the HV room, the transformer room and the LV room in separate compartments of one steel enclosure, leaving room for maintenance, and complies with GB 17467. The Chinese-style unit mounts the oil-immersed transformer outside the enclosure with independent HV and LV switch rooms, so the cooling area is larger and the transformer is easy to inspect; it is typically used for PV and wind step-up duty and for industrial supplies.

Distribution transformers cover 30–2500 kVA for 10 kV, 20 kV and 35 kV systems, with a 0.4 kV LV side in the standard ratings. The tapping range is ±2×2.5% or ±5% and the vector group can be Dyn11, Yyn0 or Yzn11. The exact figures for each model are listed in the technical parameter table on its product page.

NX1, NX2 and NX3 are the no-load and load loss levels set by GB 20052 (minimum allowable values of energy efficiency and energy efficiency grades for power transformers): the lower the number, the higher the efficiency. In the 10 kV oil-immersed range the S22 is rated to NX1 and is the most efficient of the three, the S20 to NX2 and the S13 to NX3. Among the dry-type products the SCBH19 meets national grade 1 efficiency, while the SCBH17 and the SBH21 are grade 2.

Oil-immersed distribution transformers are built to GB/T 6451 (technical parameters and requirements for oil-immersed power transformers) and the GB/T 1094 power transformer series, which corresponds to IEC 60076; dry-type units follow GB/T 10228 and GB/T 1094.11. Efficiency grades are assessed against GB 20052 and prefabricated box substations comply with GB 17467. Every unit is tested against the applicable national and international standards before it ships.