The
distribution transformer is installed in a
station having N phases, at least N-1 phases being equipped on the high-
voltage side of the
transformer with respective current-limiting fuses capable of blowing in the event of a dead
short circuit between the phases. The
protection system includes: at least one fault
detector for detecting faults on the basis of at least one of the following indicators: pressure in the tank, level of the
dielectric, or temperature of the
transformer; a short-circuiter acting on all the phases situated upstream from the high-
voltage windings, said short-circuiter being capable of being triggered by said fault
detector to establish a dead
short circuit between the phases; and on at least N-1 phases, a
detector for detecting an abnormal current upstream from the
transformer, said detector being associated with a controller for controlling said short-circuiter. In the
system, at least the phase that is not equipped with a limiting fuse is equipped with a
disconnector switch which is normally closed in the absence of any fault, said
disconnector switch being disposed on the high-
voltage side of the transformer upstream from the short-circuiter, and opening thereof being triggered by the short-circuiter in the event of a fault, but with a certain
delay.