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In practical power systems, it is still very challenging to figure out a cost-effective undervoltage load shedding (UVLS) scheme that can reliably and adaptively react to the short-term voltage stability (SVS) problem. Faced with this challenge, this paper develops an intelligent data-driven predictive UVLS scheme for online SVS enhancement. Inspired by valuable ideas in model predictive control and supplementary excitation control in power systems, a novel deep feedback learning machine (DFLM) is designed to precisely predict future voltage violations after UVLS execution. With the help of the DFLM, the UVLS scheme is aware of potential effects of various candidate UVLS actions. Owing to this desirable nature, it can adaptively respond to diverse SVS conditions and optimize UVLS decisions in a non-iterative way. Further, two well-designed strategies, i.e., stepwise constraint relaxation and incremental DFLM adaptation, are introduced to enhance the scheme's reliability and adaptability during online application. Numerical test results on the Nordic test system and the realistic North GZ Power Grid in China showcase the excellent performances of the proposed scheme. [ABSTRACT FROM AUTHOR]

In this paper, a special control solution called virtual voltage source (VVS) is developed for no-load tests of induction machines. This concept is applied to a 2 × 27 MVA high-power machine test bench where the test bench is requested to precisely characterize, e.g., 3 MW machines at no-load currents. The developed VVS thoroughly solves the stability issue of induction machines at low-speed ranges. A set of optimizations is presented here that systematically improves the voltage precision of the test bench. Experimental results prove that the proposed concept achieves 0.08–0.12% voltage unbalance, less than 3% current unbalance, with less than 0.3% harmonic-voltage-factor, and verified by more than 100 induction machines. [ABSTRACT FROM AUTHOR]

With the increasing demand of electricity, the development of the urban power grid has drawn a lot of attention in China. In order to focus on the analysis of an urban power grid, the remaining part of the large-scale power grid used is to be reduced. The accuracy of the equivalence is key to urban power grid research. In this paper, a multistep dynamic equivalent method based on district dividing is proposed. Based on the electrical distance, voltage level, and geographic location, the external system is divided into outer layer, inner layer, and buffer subsystem. Each district is separately reduced by different methods. The proposed technique is illustrated by a real large-scale power grid in the south of China. [ABSTRACT FROM PUBLISHER]

A multi-purpose balanced (MPB) transformer is proposed in this paper for electric railway applications. The MPB transformer is developed from impedance-matching (IM) transformers widely used in China's railway systems. The proposed MPB transformer has three main functions: 1) it provides a symmetrical two-phase voltage of 27.5 kV for railway overhead lines to power electric trains; 2) it supplies a three-phase balanced voltage of 10.5 kV for railway substations; and 3) it can accommodate a three-phase harmonic filter with improved power factor and reduced manufacturing cost. In this paper, the operating principles of the MPB transformer are elaborated, the design of the harmonic filters is discussed, and the results of computer simulations are provided. A 16-MVA MPB transformer was designed and commissioned, and real-time field measurements are provided. [ABSTRACT FROM AUTHOR]

This paper attempts to address the influence of sugar as a contaminant on outdoor insulation characteristics of insulators in a substation. Strong discharge activity was occurred under relative humidity less than 80% on insulators in a 500 kV substation at south China. A preliminary viewpoint that sugar as a contaminant leads to this strong discharge was drawn by investigating pollution sources around the substation and analyzing pollution layer conditions of discharged insulators. In order to further confirming this viewpoint and proposing the appropriate solutions for avoiding this discharge activity, the outward appearance, the surface conductivity, the discharge inception voltage and the flashover voltage of glass insulator and room temperature vulcanized (RTV) coated insulator under sugary and non-sugary contamination were investigated in detail in the lab. Furthermore, the hydrophobicity and hydrophobicity transference of RTV coated insulator were also investigated. The research results show that sugary contamination is very absorbent and viscous, outdoor insulation characteristics of insulators covered with sugary contamination are worse than that covered with non-sugary contamination, but outdoor insulation characteristics of RTV coated insulator covered with sugary contamination is still better than that of non-RTV coating insulator with non-sugary contamination. So it is still a specific solution to inhibit the discharge activity of insulators in the substation by spraying RTV coating. Of course, removing the sugar canes themselves from this area is the best solution. [ABSTRACT FROM PUBLISHER]

Jinsha River has very abundant hydro power reservation, ranking first in all the hydro power bases of China. To deliver the 38-GW hydro power from Jinsha power stations by HVDC transmission lines to load centers 1000-2000 km away, it is necessary to determine the right voltage level and the capacity of each bipole. This paper proposes three preliminary power delivery scheme and presents an optimization method for transmission capacity, dc voltage and conductor size. Based on a comprehensive comparison of cost-effectiveness, technical feasibility and network security and stability, it was recommended that the 3 bipolar ±800-kV ultra HVDC (UHVDC) links with rated capacity of 6.4 GW for each link be adopted as transmission scheme of Phase I Hydro Power station on Jinsha River. [ABSTRACT FROM AUTHOR]

The dc arcing performance of composite insulators with contaminated surfaces has been investigated at high altitudes because of the program of building ±800 kV dc transmission lines in China, because much of their intended routes will be at relatively high altitudes. As the length of the arcs on the composite insulator depends on the repeat distance and the arcs are initiated on the core rod between the sheds, the effect of the repeat distance and the shed dimensions on the dc flashover voltages was studied for composite insulators under contaminated conditions. The experimental results confirmed that the shed design parameters do have a great influence on the flashover voltages. It was found that, with the same insulation distance, the flashover voltage had a maximum at a particular value of the radial extent of the shed and of the betweenrepeat distance, and that the influence of these two factors on the flashover voltage was independent of each other. It was also found that, for the alternate large and small shed design, the ratio of the radial extent of the major shed to the minor shed should not be too great. [ABSTRACT FROM AUTHOR]