Resistance of transformers to internal faults: synthesis of experimental results

The series of tests conducted by EDF between April 1984 and January 1987 provided important experimental experiences of the behavior of MV/LV transformers in the event of internal faults. The results of these tests showed that an insulation fault between LV turns gives rise to the most violent external manifestations. In addition, whatever the type of fault, the melting of the links between the MV terminal and the MV windings is likely to create an arc in the transformer envelopes of an expansion and energy such as to lead to extremely rapid explosion of the transformer. In both these cases-fault between LV turns and melting of MV links-the experimental results obtained also showed that MV fuses today would seem to be the most suitable means of providing effective protection of transformers, due to their ability to limit the duration and amplitude of the high short-circuit currents which cause the explosions and which were reproduced in the laboratory