Tripod transformer tames solar storms

ABB has delivered a three-legged transformer designed to protect a Swedish nuclear power station from solar flares which can cause city-wide blackouts

The three-phase 825 MVA, 420/21 kV generator step-up transformer contains one of the largest and heaviest transformer cores that ABB has ever built.

Equipped with three limbs instead of the usual five, the transformer is designed to improve availability and protect the Oskarshamn 2 nuclear power plant in Sweden from solar flares or solar storms, more correctly called geomagnetic induced currents (GIC).

Solar flares unleash magnetic storms that hit the earth’s magnetic field and create geomagnetic currents that can enter power lines and the neutral point of transformers. GICs frequently lead to severely damaged transformers and voltage collapse at a cost of millions of euros per hour in lost revenues and damaged assets.

The most powerful GIC ever recorded at a power plant struck Oskarshamn in 2000, and in 2003 another GIC tripped several power lines and transformers all over the country and caused a blackout affecting 50,000 consumers.

To prevent the same thing from happening again, Oskarshamn, which is jointly owned by E.ON and Fortum, asked ABB to design an 825 MVA transformer that would be immune to solar storms.

Transformers larger than 200-300 MVA are usually built with five limbs, but for Oskarshamn 2, ABB made a three-limbed transformer, as these provide the most effective protection available against GICs.