Numerical simulation of lightning-caused inrush currents in power distribution transformers

Arresters connected in parallel with distribution transformers limit lightning caused over-voltage to the residual voltage which due to long duration lightning strikes, may cause magnetic saturation of the transformer core. This, in turn, leads to transient currents which may cause nuisance operation of fuses. In this paper the influence on current, voltage and transient of lightning current amplitude, duration and the phase angle of the AC voltage at the moment of lighting strike has been simulated. The simulation results indicate that a long duration lightning current, even with low amplitude, may cause transformer core saturation and inrush current. The simulation results may be helpful in the assessment of lightning performance of operating transformers and arresters and the design of suitable schemes to minimize nuisance fuse operation and the specification of guidelines for fuse selection and arrester ratings.