Study On Development Of Typical Partial Discharges In Power Cables Joint

Prefabricated cable joint with silicone rubber insulation is the high-risk area of cable faults. Existing measurement and analysis technology of partial discharge (PD) cannot be used to effectively evaluate the insulation state of cable joint, because the relationship between microscopic physical process of silicone rubber insulation deterioration and macroscopic characteristics of PD has not been established yet. And PD activities in whole process from insulation deterioration to breakdown is lack of record, thus it is unable to assess the PD severity. To solve these problems, firstly, the relationship mentioned above was built, on this basis an in-depth study on the evolution process of PD caused by typical defects was carried out, and eventually the method to estimate the PD severity has been put forward.Based on35kV cable and prefabricated cable joint, the experimental platform of PD measurement was set up. Besides a coaxial cylinder sensor which can measure PD of cable joint in real time and high sensitivity has been developed. Experimental results show that its sensitivity achieves10pC, which can meet the requirement of PD measurement in cable joint.To study the relationship between physical process of silicone rubber insulation deterioration and PD characteristics, the samples of silicone rubber defects were prepared. In the process from insulating degration of silicone rubber to breakdown, the photos of electrical treeing and PD signals were simultaneously recorded. And then two curves, both electrical treeing area and PD energy in unit time changing with time, were generated. Elaborating the corresponding relation between the two curves, it was found that the growing trends of two curves are in high consistency, which lays the foundation for the state evaluation of silicone rubber according to PD information.To study the evolution process of PD caused by typical defects in cable joint, four types of typical defects, including shield spine, microvoid, surface metal particles and surface spine, were designed and made in real35kV prefabricated cable joint. For each defect model, reasonable methods of applying voltage were designed to stimulate and accelerate the evolution of PD signals, meanwhile, the coaxial cylinder sensor was used to measure the PD signals in the whole process, and then insulation damage caused by discharge was observed and explained, afterwards, the curves of PD characteristic parameters (including discharge times per unit time, average discharge energy and total discharge energy) changing with time were generated. In accordance with the change rules of these curves, the method to divide the evolution stages of PD was proposed. And then phase resolved partial discharge (PRPD) spectra in each stage were obtained and analyzed, furthermore, the physical process of PD evolution caused by typical defects in cable joint was expounded.To study the assessment method of PD severity caused by typical defects in cable joint, the characteristic quantities standing for PD fingerprint information were extracted from PRPD spectra in each stage, and then the relationship between PD characteristic quantities and PD evolution stages were set up, from which the change rules of PD characteristic quantities in the evolution process can be summarized. Based on the PD severity, the evolution stages were divided into PD initial stage, developmental stage and severe stage. Combining the change rule, damage phenomenon caused by discharge and statistical characteristics of PD, the main features of each stage were expounded, and on this basis the method to assess the severity of PD was put forward.