The present invention belongs to the field of on-line monitoring and fault diagnosis of a transformation device in a power
system, and relates to a new failure mode based method for calculating a
failure probability of the transformation device. The method in particular comprises: according to an established device fault tree, calculating an
occurrence probability Pi(i=1,2...n) of various failure
modes, severity Ii(i=1,2...n) of various failure
modes, and criticality of various failure
modes Wi(i=1,2...n) on the device. According to the present invention, when the various failure modes are mutually independent, a
device failure rate
lambda caused by the various failure modes can be computed according to a series model of a failure
reliability theory, i.e., (reference to the specification), wherein computing of the defect
occurrence probability Pi of various failure modes of transformation device is based on a defect probability computing method of an online
monitoring data statistic probability distribution regulation; computing of the severity Ii(i=1,2...n) of defect corresponds to various failure modes is obtained according to the development process of a device defect, and developmental and changing rules of a characteristic parameter; and the criticality of various failure modes Wi is obtained by using a fuzzy
hierarchical analysis method.