Research On Insulation Failure Mechanism And Measurement Technology Of High-Voltage Storage Capacitors

Pulse power system has been widely used in high technology fields, whose developing direction is high storage density, light weight and small volume. Its kernel problem is to establish a pulse power storage system with high storage density. High storage density capacitor is one of the important research projects. Improving the storage density of capacitors, it means decreasing the volume and increasing the storage energy capability of dielectric. This brought out hidden trouble to the insulation capability and the work reliability of capacitor. As for the especially work condition of high-voltage storage capacitor, traditional measurement for leaving factory can not predict the insulation status and life of capacitor. So, the capability estimation of high voltage storage capacitor is the key technology for safety action of pulse power system. Based on the domestic and international research results of storage capacitor, the research on high voltage storage capacitor is processed in the thesis, that include detection technology for insulation capability and aging mechanism under large impulse discharge. This research results would effectively promote the design, manufacture and estimation work on storage capacitor for guaranteeing the work capability of pulse power system.The work process of high voltage storage capacitor is charge under DC and large discharge in short time. Such process is the main course insulation was aged. In general, partial discharge, space charge, mechanic and heat act as the main aging effects to insulation. However, under large impulse condition, they have different action degree to insulation. Long time partial discharge action is one of the main reasons leading dielectric of high voltage storage capacitor invalidate. Injection and detrapping of space charge would also result in polymer degradation, even breakdown. According to the low work frequency of capacitors researched here, aging function degree from thermal field is unobvious, while the stress would just accelerate the aging process.It was found that there is similar voltage regulation between large impulse discharge and square pulse. Voltage regulation, which means du/dt, did great effect on the space charges density and the occurrence of PD. So the research theory of insulation degradation under square pulse could be applied to insulation estimation under large impulse discharge. As for the large current magnitude of large impulse, partial discharge data can't get through sensor directly under such impulse. On account of the workprocess of high voltage storage capacitor, partial discharge measurement during the charge period was put forward. It is PD measurement under DC voltage. With the principle analysis and discharge simulation of DCPD, there is a relationship between discharge parameters and insulation defect characters. So DCPD would effectively reflect the capability of insulation.According to the manufacture technology and aging effect, the defects of capacitors were divided into inner defect, contact defect, overlap defect and oiliness defect. Through the finite element analysis, electrical field distribution of above four defects was simulated during the large impulse process. Moreover, partial discharge under DC was measured with wide-band detection resistance on classical defects of insulation. Distinguishing PD parameters among inner discharge, surface discharge and corona discharge, the waveform characters and frequency spectrum energy distribution was confirmed.Based on the knowledge of DCPD signals, a DCPD detection system was established. To decrease the inference from supply source and outer space, it used impedance balanced detection way for detecting PD signal. Because of the randomicity of DCPD signal, DCPD data was acquired by trigger way. As an effective parameter,â–³t was inducted in the analysis. Based on q,n andâ–³t, the discharge spectrum and fingerprint statistic spectrum was calculated out for capacitor PD signal analysis.DCPD detection principle should take into account the rise time of DC source. It can be divided into two sections, transition period and flat period. Based on such measurement rule, figures discriminations were processed on four defects measurement results. Thereinto, inner defect and oiliness defect were compared by simulation and measurement results, which proved that the PD in inner defect was more severe than in oiliness defect. Due to different aged degree of capacitor, DCPD measurement was processed with the same connection form and the reverse one. The PD parameters had relationship with the aging times of capacitors. However, the results would be effect by PD and space charge, which means PD action was influenced by different distribution and amount of space charge.