Below roughly ten tonnes a transformer normally travels fully assembled and oil-filled on a reinforced pallet or skid. Above that you increasingly drain the oil, ship the tank under dry nitrogen, remove bushings and radiators, and fit a shock recorder. The rules behind both cases are the same: keep the unit upright, keep moisture out, and be able to prove on arrival that nothing was dropped.
Preparing the unit for the road
For a large power transformer the oil is drained and the tank filled with dry nitrogen at a slight overpressure, typically in the region of 0.1 to 0.3 bar, so that no moist air can enter through a seal. The pressure is recorded at dispatch and checked again on arrival. A pressure that has dropped to zero means the tank has breathed, and the unit needs internal inspection and drying before it is filled and energised.
Bushings, the conservator, radiators and cooling fans come off and are crated separately, with every opening blanked off. Loose internal parts are secured, the breather is sealed, and desiccant goes into the accessory crates. Smaller units keep their oil, which is simpler and safer, provided the oil level allows for expansion and the unit stays upright.
Shock indicators are the evidence, not a formality
Fit a three-axis impact recorder or single-use shock indicators to the tank, usually set around 3 g. Photograph them on arrival before anything is offloaded and before the consignment note is signed, because after that the discussion about who caused a fault becomes considerably harder.
If an indicator has tripped, do not energise. Inspect internally where access allows, check core and winding clamping, and repeat turns ratio, DC winding resistance and a dissolved gas analysis before commissioning. A tripped indicator is not proof of damage, but it is proof that you have to look.
Lifting, lashing and the angles that matter
Lift only by the designated lifting lugs, never by the cover bolts, the radiators or the bushings. Use a spreader beam so the slings stay close to vertical, and work from the centre of gravity marked on the nameplate rather than from the visual centre of the tank. Jacking pads are for jacking and skidding; they are not lifting points.
Secure the unit with certified lashing to the certified points, chock the skid so it cannot slide, and keep every strap clear of bushings, radiators and the control cabinet. Manufacturers commonly give a maximum tilt of around 15 degrees during handling; exceeding it can move oil into places it should not be and shift the core assembly.
What to check the moment it arrives
- Read and photograph the shock indicators before offloading begins.
- Record the nitrogen pressure, or the oil level and temperature on a filled unit.
- Inspect for leaks, dents, paint damage and missing or damaged accessory crates.
- Note any damage on the consignment note before signing it.
- Take an oil sample as the transport baseline on filled units.
The practical trade-off is between effort at the ends and risk in the middle. Draining and nitrogen-blanketing adds a day at dispatch and requires vacuum filling and a settling period on arrival, but for a heavy unit it removes several tonnes and the risk of oil surge. Under about ten tonnes, shipping filled is normally faster and no less safe. Protrafo arranges route surveys, abnormal-load permits and crane coordination across Europe when the unit is large enough to need them.
