Earthing, lightning protection and thermography report for a wind farm collector substation

What the insurer was asking

The policy was up for renewal subject to a report on the earthing and lightning protection system of the collector substation, which takes power from nine turbines over 34.5 kV lines. The last document dated from commissioning, four years earlier, and carried no real fault current: it used the short-circuit figure from the design sheet, taken before the farm went live.

Field metering

• Earth resistance by the 62% method and by potential fall in three directions, compensating for resistive soil
• Touch and step voltage at the highest-gradient points, using the fault current confirmed by the utility
• Inspection of down conductors, exothermic welds and continuity between the mesh and the tower bases
• Thermography of the two transformers, bypasses and disconnectors under generation load, at the hour of highest output

The mesh passed the resistance criterion and failed the gradient one: three gates and one disconnector control box sat above the admissible limit for the current fault level. The report listed 21 non-conformities, ordered by risk rather than by how visible they were, each with a suggested deadline and a cost band for the fix.

A useful report does not end at the stamp: it ends in a queue of corrections that maintenance can execute in the right order, with the money that actually exists.