Research Status of Online Monitoring of Insulation Monitors at Home and Abroad
The IT grounding form of the low-voltage power distribution system, that is, the neutral ground-to-ground insulation of the power supply, the exposed conductive part (metal casing) of the electrical equipment is directly grounded, and the load side is only protected. For the downhole low-voltage distribution system, the power supply is the secondary side voltage of the 〇. 4 kV transformer. When the IT system has the first single-phase ground fault (single-phase insulation breakdown), it may not be detected in time. It will be possible to develop into the second ground fault of the IT system, resulting in a large short-circuit current, threatening equipment and personal safety.
Developed countries such as Europe and the United States have applied insulation detection technology extensively in IT distribution networks. More importantly, after long-term online operation, developed countries have accumulated a large number of monitoring results, enriching the criteria for cable defects and aging. At present, domestic research in this field is still in its infancy, and many scholars and research institutes have tracked foreign monitoring techniques and methods [5, but few online insulation monitors have been put into operation.
The main methods for online diagnosis of cable insulation are DC superposition method, DC component method, online tan8 method, low frequency superposition method, and AC superposition method. Among these methods, the DC component method and the AC superposition method are still in the theoretical research stage; the online measurement tanS method reflects the general defect, while the individual concentrated defects do not cause significant changes in the tanS value, and the tanS value is susceptible to Interference can not accurately measure cable insulation defects. This paper considers the low-frequency superposition method, which can not only measure the insulation resistance and capacitance to ground, but also has relatively small interference and small measurement error.
