Low-voltage-side current-surge phenomena in single-phase distribution transformer systems

Lightning current surges entering the secondary windings of distribution transformers can be a cause of transformer failure. Proposed solutions have included interlacing the secondary windings and applying low-voltage arresters. Tests have been proposed to verify the ability of a transformer to withstand these surges. It is shown that the amount of current varies significantly for different sizes and designs of transformers, loads, and secondary cables. It is also shown that the entire secondary circuit must be treated as a system. Measures taken to protect the transformer generally increase the surge voltage stress on the load equipment. The source of the problem is the voltage drop along the secondary cable. Minimizing that voltage can effectively alleviate the problem of both transformer and load. These facts must be taken into consideration before developing transformer test standards to address the low-voltage-side current surge problem