The Real Cargo Is the Insulation, and Moisture Destroys It
A transformer looks like a steel tank, but what you are really shipping is a dielectric system: windings, paper insulation and oil whose performance collapses the moment moisture gets in. Insulation that absorbs water during transit fails its dryness and dielectric tests at site and must be vacuum-dried before the transformer can be energised, weeks of delay on a critical-path asset. The exposed sub-assemblies are just as unforgiving: porcelain bushings crack under shock, radiators and conservators distort if shipped attached, and any open flange is a path for moist air into the active part.
BENZ ships a transformer the way the manufacturers specify it. For transport the oil is drained and the tank is filled with dry, pressurised nitrogen to hold the active part moisture-free, with the pressure monitored and a "Do Not Open — Nitrogen Pressurised" control on the tank; the oil travels separately in sealed drums or a flexitank. Bushings of 69 kV and above are removed and crated individually in heat-treated boxes, radiators are demounted and separated with timber, and every tank opening is closed with a gasketed blanking plate. The tank is then cradled and crated on a heat-treated, ISPM-15 base rated to its tonnage, weatherproofed for the voyage.