Keep each transformer, ring main unit and distribution board on one build record.

Power distribution equipment is built to a utility or contractor specification, and the buyer often reviews the design before a single lamination is cut. Core stackers, winders, welders and oil-filling crews all work to one drawing and one delivery date. A distribution transformer needs different records from a feeder pillar, even when both arrive through one tender and leave on one schedule. The paperwork differs more than the steel does.

Build and test tracking here centres on the serial number, which ties core steel, winding copper and oil to the unit. The routine test report rides with dispatch. Each transformer leaves with its own test sheet.

Tenders arrive from utilities and large contractors, carrying kVA rating, voltage class, loss limits, tapping range, impedance and delivery schedule. The estimator prices CRGO core steel, enamelled copper, oil, tank and fittings, and the offer carries a loss figure the plant must later meet on the test bay. Pricing is a promise. After the order is confirmed, the design office submits drawings and a parts list, and the utility returns marked-up copies repeatedly until one final set gets its signature. Round two is normal.

Core laminations are cut and stacked with step-lap joints, then coils are wound and baked, assembled on the core and dried in a vapour phase oven. The active part is lowered into the tank and fitted with bushings, tap changer, Buchholz relay and conservator before any oil goes in. Ratio, winding resistance, insulation and loss tests follow once the unit is full, and a utility inspector may be called to witness them. The date is fixed well ahead, so the unit must already be dry, oil filled and tested when the inspector walks in. Distribution boards and feeder pillars take a lighter route through sheet metal fabrication, busbar fitting and wiring, though dispatch still needs serial plates and a test report. No report, no truck.