The partial discharge（PD） is widely regarded as an important index for insulation state monitoring at home and abroad

however

assessment for insulation conditions of oil-paper in power transformers based on PD has no wide practical application. Therefore

we summarized the research status of insulation condition assessment of oil-paper in power transformers based on PD

and proposed its directions which need to be studied in depth and its growing trend

providing the basis for subsequent research. By analyzing PD characteristics of oil-paper insulation

discharge pattern recognition of oil-paper insulation

aging assessment of oil-paper insulation and defect development degree diagnosis of oil-paper insulation

the conclusions can be drawn as follows: the initial discharge characteristics and waveform characteristics of PD under different types of electric field are different

the recognition rate can be 95% using the time series spectrogram combined with the phase-resolved partial discharge（PRPD） spectrogram

the method of extraction

dimension reduction

classification and intelligent arithmetic are necessary four steps for oil-paper insulation assessment

and PD degree can be divided into four stages as starting stage

developing stage

severity stage and detriment stage. This research shows that the sensitivity classification of characteristic quantity according to different problems and comprehensive analysis of aging assessment and defect development degree diagnosis requires depth research. In addition

the insulation condition assessment of oil-paper in power transformers based on information fusion including PD is the future development trend.