Voids or cracks in basin insulators inside a GIS (gas-insulated metal-enclosed switchgear) could trigger partial discharges or surface flashover under electrical stresses, threatening safe GIS operation. For this paper, some epoxy composite specimens were made from similar materials and manufacturing processes to make 252 kV GIS basin insulators. Some voids with different diameters or cracks with different diameters and orientations were artificially made in the specimens with different thicknesses. An ultrasonic pulse-echo system was set up, and ultrasonic tests were carried out on the specimens with voids or cracks. A method to calculate the depth of a defect was proposed by the propagation time of defect reflected waves. The results showed that a depth of 50 mm, a diameter φ of 2 mm void, and a diameter φ of 1 mm crack in epoxy composite insulation were detected by the ultrasonic system using a 1 MHz transducer.

Internal stress in basin insulators of gas-insulated metal-enclosed switchgear (GIS) can lead to cracks, which affects the safe operation of these apparatuses. In this research, we proposed a subsurface internal stress measurement method for GIS epoxy composites. This method is based on an ultrasonic longitudinal critically refracted (LCR) wave technique. In this study, some epoxy composite specimens were synthesized with similar materials and manufacturing processes to those of 252 kV GIS basin insulators. An ultrasonic stress measurement system that utilized the LCR wave technique was set-up to investigate the relationship between stress and LCR wave propagation time, as well as to measure the compressive stress of the epoxy specimen within 0–50 MPa. The results show that LCR wave propagation time linearly decreased when stress increased in the subsurface zone and the acoustoelastic coefficient was −4.95. We found the relative errors of stress measurements to be less than 13%.

Situations of internal stress in basin insulators inside gas-insulated metal-enclosed switchgear (GIS) can lead to cracks, which can influence the safety and stability of apparatus. However, there is currently no research on internal stress measurements for composites of GIS basin insulators, and only measurements for surface stress. In this paper, an internal stress measurement method for GIS epoxy composite is proposed using an ultrasonic longitudinal through-transmission technique based on the acoustoelastic effect. An internal stress measurement system is developed to investigate the relationship between the uniaxial compressive internal stress and the velocity of the ultrasonic wave vertical to the stress in epoxy composite within a range of 0-70 MPa, and to calculate the acoustoelastic coefficient of epoxy composite. The effects of system delay are eliminated in measuring the propagation time. Some epoxy composite cuboid specimens with similar materials and using a manufacturing process similar to those of 252 kV GIS basin insulators are synthesized, and the uniformity of the internal stress in cuboid specimens is verified by finite element simulation. The results reveal a linear increase of the ultrasonic longitudinal wave velocity with increasing stress. It has been shown that the average acoustoelastic coefficient of GIS epoxy composites, using the longitudinal waves vertical to the stress, is 4.556 × 10 −5 /MPa. Additionally, the absolute errors of the internal stress measurements are less than 12.397 MPa. This research shows that the ultrasonic method based on the acoustoelastic effect for measuring the internal stress in GIS epoxy composites is feasible.

Emergency voltage control provides a real-time online response to maintain the long-term voltage stability of a power system. Searching for an optimal emergency control solution is a hard combinatorial optimization problem because of the highly dynamic and nonlinear characteristics of power systems with discrete control variables. Additionally, real-time response is required. A new mode-matching–based adaptive voltage control is proposed in this article to achieve a fast response by exploring local voltage profile modes and the technique of similarity ranking. First, some typical emergencies are studied in advance, and their control knowledge is collected for preparation. The set of local voltage profile modes and their corresponding optimal control solutions are stored as knowledge for each emergency. Second, fast online control is realized and the control solution is configured according to a similarity ranking among local voltage profile modes. Furthermore, a learning process is applied to accumulate knowledge in case of unprepared situations. Thus, improved control performances in the future are ensured. This article depends on a new concept of local voltage profile mode with which knowledge preparation, emergency identification, configuration of control, and knowledge accumulation work together to perform an effective response. Simulations of the IEEE 39-bus system verify the outcomes of this voltage control scheme.

No abstract