To solve problems like complex internal causality of large-scale thermal systems

poor real-time

low resolution ratio of fault diagnosis systems and other ones

the formal definition of hierarchical orientation graph model based on signed directed graph(SDG)was proposed.Moreover

a fault diagnosis method was also put forward

on the basis of the improved hierarchical directed graph.In this method

a directed graph segmentation strategy is applied to reduce the search space for failure source;and the qualitative relationship on the backward path of failure alarm node is used to search for compatible branch to determine the source of the fault candidate nodes.Furthermore

this method was applied on a deaerator system for fault diagnosis

and the results were compared with that obtained by the conventional SDG fault diagnosis method.The results show that

search space of this hierarchical orientation graph diagnosis method is dramatically smaller than that of the conventional method

indicating this new method can improve the diagnostic system speed

make the resolution ratio of the source of fault nodes reach 100%

which meets requirements of real-time.