Partial discharge (PD) inside insulation is considered as one main reason that lead to electrical equipments damage, and discharge patterns are closed related to the types of internal defects. As one of the major methods to find out discharge faults and diagnose internal defects, the technologies of PD on-line monitoring and pattern recognition are of importance for the diagnosis of the quality of HV insulation system, and of importance to the safety and reliability of electrical equipment in service. The n...