Abnormal Currents in Distribution Transformers Due to Lightning

Abnormal currents in distribution transformers due to lightning are analyzed both theoretically and from field experiences. Under certain conditions of direct stroke transferred through the arrester to the neutral of the secondary winding, excessive currents may wreck the secondary windings by electromagnetic forces. Long-duration surges, or shorter repeated surges, saturate the transformer cores producing greatly increased surge currents in the primary windings which influence fuse failures. The saturation of the cores by unidirectional lightning surges also brings about increased power-frequency magnetizing currents influencing sectionalizingfuse and circuit-breaker operations.