Transport, unloading and installation of a distribution transformer: the checklist

A distribution transformer is a robust piece of equipment – but a 2 500 kVA unit weighs close to six tonnes, and most damage we see happens in the last 50 metres of its journey. This checklist covers what to prepare before the truck arrives.

1. Know the mass and dimensions

Rating	PNACHO-O total mass (approx.)	PNACHO-D total mass (approx.)	Length × width × height (oil, approx.)
250 kVA	1 100 – 1 200 kg	1 100 – 1 400 kg	930 × 720 × 1 400 mm
630 kVA	1 800 – 2 300 kg	1 700 – 1 900 kg	1 100 × 900 × 1 750 mm
1 000 kVA	2 700 – 3 150 kg	2 550 – 2 750 kg	1 200 × 910 × 1 950 mm
1 600 kVA	≈ 3 800 kg	3 550 – 4 000 kg	≈ 1 950 mm long
2 500 kVA	≈ 5 800 kg	≈ 5 200 kg	≈ 2 100 mm long

Exact values for each ratio are on the data sheet; always use the data sheet of the delivered unit, not a catalogue value.

2. Unloading

• Lift only at the lifting lugs (four on oil units, on the top frame of resin units) with slings of the correct angle – never at the bushings, the tap changer or the cooling fins.
• A crane or a forklift with sufficient capacity and fork length; the centre of gravity is high, especially on oil units.
• Rollers: PNACHO-O units have bi-directional rollers; use them for the last metres on a hard, level floor. Pull at the haulage lugs on the base frame.
• Check the unit on arrival: paint damage, oil traces under the tank, bent fins, cracked bushings. Note anything on the delivery note before signing.

3. Foundation and clearances

• Level concrete floor or beams designed for the mass plus a dynamic factor of 1.5.
• Rails or a flat floor for the rollers; lock the rollers or fit anti-vibration pads once in position.
• Minimum clearance to walls: 300 mm on the fin sides for cooling, more if the room is small. Around live HV parts of a cast-resin unit: as required by the local regulations (typically ≥ 750 mm to a wall for 24 kV, or an enclosure).
• Oil-immersed units indoors: an oil pit or bund able to hold the full oil volume (≈ 360 kg / 400 l for a 630 kVA unit), unless local rules exempt hermetically sealed units below a certain volume.

4. Ventilation

All losses become heat in the room. For natural ventilation, the inlet opening (low) and the outlet opening (high, on the opposite wall) should each provide a free area of about S ≈ 0.18 · P / √H, where P is the total loss in kW and H the height difference between the openings in metres. For a 630 kVA oil unit (≈ 5.2 kW total losses) and H = 5 m that is about 0.45 m² – many designers double it to allow for grilles and dust. Forced ventilation: about 4–5 m³/min of air per kW of losses.

5. Before energising

1. Remove transport locks; on resin units check that the coils did not shift.
2. Oil level indicator in the normal range; no oil traces.
3. Tap changer on the position agreed with the grid operator, locked.
4. Earthing terminals connected; neutral earthed per the network scheme.
5. Insulation resistance measured (see our commissioning checklist).
6. Protection relay (DGPT2 / PT100 monitor) wired and tested.

Keynetgrid delivers to any EU country with crane unloading and placement on request – details under Services. Masses, dimensions and drawings for each unit are on the product pages of the PNACHO-O and PNACHO-D ranges.