The project belongs to the field of high voltage engineering, involving multiple majors such as transformers and electrical measurement. It took 13 years with the support of the National Natural Fund and others and was completed through a collaborative approach combining industry, academia, research and application. With the increase of voltage levels, the insulation level of electrical equipment has become the primary factor affecting the difficulty of equipment manufacturing and the safe and stable operation; transformers are the hub equipment of the power grid, and the test and diagnosis technology of insulation defects plays an increasingly important role in quality monitoring and risk management. The operation analysis of transformers with voltage levels of 220kV and above from 2013 to 2018 by China Electric Power Equipment Management Association shows that the most faults/defects occurred in the body windings and insulation, accounting for about 40%; the insulation faults/defects originated from product design, manufacturing process, quality of outsourced parts, transportation and operation (Electric corrosion, thermal cracking, moisture) and other aspects; Partial discharge (PD) caused by insulation defects is the primary cause of exacerbating the aging of oil-paper insulation of operating transformers and evolving into insulation breakdown failure. Based on the types of voltages borne by AC and converter transformer oil-paper insulation systems, the project team explored the discharge mechanism of typical insulation defects under different types of voltages, and combined with the actual needs of on-site test and testing, carried out key PD diagnosis technologies suitable for transformers., online monitoring or live detection, and achieved the following innovative results: 1) Grasping the PD characteristics of the transformer under composite voltages such as AC, DC, impulse and DC superimposed power frequency, revealing the discharge mechanism of typical defects such as the middle tip plate, internal air gap and surface of oil-paper insulation, obtaining the PD origin to the entire process of insulation breakdown, and proposing an analysis method for PD mode classification; 2) Through simulation and experiments, the propagation characteristics and laws of PD ultra-high frequency electromagnetic waves in the internal and surface gaps of the transformer are obtained; The narrowband sampling technology based on the mixing principle has been overcome, and the transformer PD ultra-high frequency online monitoring system has been developed. The technology that can avoid the impact of communication interference online in real time has reached the international leading level; 3) For the first time, a rapid pulse burst classification technology suitable for multi-local discharge source detection and noise source separation was proposed, and a broadband detection and identification system for DC multi-local discharge sources for converter transformers was developed, realizing the rapid separation of multiple local discharge sources and noise sources, laying the foundation for on-site DC withstand voltage PD test of converter transformers; 4) The inductive principle is proposed to generate high-efficiency oscillating operating impulse voltage for on-site impulse withstand voltage PD test of transformers. A mobile test device is developed, and the oscillating phase analysis method is used to solve the problem of PD analysis and pattern recognition under impulse voltage. The overall technical level is internationally leading. The project was authorized for 7 invention patents and 3 utility models; 20 academic papers and works were published, including 4 SCI articles, 12 EI articles, 3 core Chinese articles, and 1 monograph. He cited 748 times at home and abroad; and 2 standards were compiled. The appraisal committee organized by China Electrical Engineering Society in 2019 believed that ldquo; the project results have reached the international leading level in broadband detection and identification technology of DC multiple local discharge sources for converter transformers, and partial discharge detection under the impact of oscillating operation of large power transformers rdquo;. At present, a variety of PD test and detection systems and devices corresponding to the project results have been commercialized in many domestic commercial companies and are widely used in State Grid, China Southern Power Grid and Singapore Power Grid, effectively promoting transformer quality monitoring and safe operation. The development of support technology has increased, with an added output value of 117.07 million yuan, a new profit of 19.91 million yuan, a new tax of 11.71 million yuan, a foreign exchange revenue of 820,000 US dollars, and a capital saving of 32.4 million yuan, with significant economic and social benefits.