The invention provides an automatic capacity regulating
distribution transformer and a capacity regulating method thereof. The
distribution transformer comprises a
transformer core, a capacity regulating switch, a
load control switch and a comprehensive monitoring controller, and further comprises a
transformer casing, wherein the capacity regulating switch and the
load control switch are integrally designed and are suspended inside the
transformer casing to be connected with the transformer core, the comprehensive monitoring controller is suspended out of the transformer casing, and is connected with the capacity regulating switch through a cable. The capacity regulating switch is composed of a permanent
magnet operation mechanism and a disc-shaped switch, a fixed contact of the disc-shaped switch is connected with high and
low voltage windings of the transformer core respectively, transformation of the
low voltage winding is completed before the
high voltage winding because the separated distances of a moving contact relative to the fixed contact are different during capacity regulating, so that currents born by a
low voltage contact are reduced greatly, and
ablation degree of the contact is alleviated; the comprehensive monitoring controller controls action sequences of a capacity adjusting
negative control switch based on the action characteristics of the capacity regulating switch and the
load control switch, capacity regulating is completed in an on-off period of the load
control switch, and capacity changing time is shortened to be within 20ms.