The power demand increases rapidly in China; however, the areas of huge power demands are of long distance from most areas of abundant energy resource in the country. Therefore, China put in great effort to develop ultrahigh voltage (UHV) power transmission systems to optimise its energy allocation. This includes (i) systematically developing key technologies such as overvoltage suppression, external insulation design, and electromagnetic environment control, and (ii) developing key equipment such as UHV alternative current (UHVAC) transformers, circuit breakers, and series compensated equipment, and UHV direct current (UHVDC) converter transformers, smoothing reactors, converter valves, and DC transmission control and protection systems. Eight AC UHV projects and 11 DC UHV projects have been built in China, which play an important role in the optimal allocation of energy. Plus there are one more UHVAC and three more UHVDC transmission projects in construction, while UHVAC gas-insulated lines will be applied in the UHVAC line crossover the Yangtze River and the ±1100 kV UHVDC power transmission technology is in development. Here, the development and application of UHV power transmission technologies in China are described, some main challenges the UHV projects encountered are discussed, and experiences obtained from the operation of UHV systems are introduced. It is concluded that China obtained mature experience in developing, constructing, and operating UHV systems and successfully realised long-distance, large-capacity power transmission, and the UHV power transmission technology has become an important measure for energy allocation in large areas.

Pulsed discharge plasma and its application is one of the promising directions in civilian areas of pulsed power technology. In order to promote the research and development of the theory and application technology for pulsed discharge plasma, in this paper, recent progress on the mechanism of nanosecond-pulse gas discharge and the characteristics and applications of typical pulsed plasma at the Institute of Electrical Engineering, Chinese Academy of Sciences is reviewed. Firstly, progress on mechanism of nanosecond-pulse discharge based on runaway electrons and measurement technology of runaway electrons is introduced. Then, the characteristics of three typical discharges, including direct-driven pulsed discharge, pulsed dielectric barrier discharge and pulsed plasma jet, are reviewed. Furthermore, typical plasma applications of pulsed plasma on surface modification and methane conversion are presented.

In recent years, the inclusion of flexible AC transmission systems (FACTS)-based compensating devices such as a thyristor-controlled series capacitor (TCSC) and a unified power flow controller (UPFC) has been increased in high-voltage power transmission systems due to numerous technical and economical benefits. However, the operation of such FACTS devices introduces harmonics and non-linearity in power system and causes fast changes in line impedance. As a result, the most widely used fixed impedance setting based distance relaying scheme finds limitation in protecting such compensated lines. Significant research has been carried out in recent years to develop new algorithms and methods to address the problem. This paper presents a comprehensive review of recent developments in the protection of TCSC/UPFC compensated high-voltage transmission lines. The relative merits and demerits of each of the available methods are also presented for comparison. Prior to detail review, the impact of TCSC/UPFC on distance protection is evaluated by using data generated through EMTDC/PSCAD on a 400 kV two-bus test power system. This study can be useful to both academic researchers and practicing engineers to gain insight on the protection of FACTS compensated transmission lines and for further development of newer algorithms.

High-voltage equipment involves both electrical and electronic components. In electrical power network, which consists of rotating machine, power transformers and transmission lines, field enhancement at critical regions can lead to local breakdown [partial discharges (PD)]. The continuous occurrence of PDs can lead to complete breakdown. While in large power equipment sharp edges can be avoided, this is not the case in power converter due to the miniature nature of the semiconductor device. Sharp edges can also be present in any power equipment in the shape of conducting particles, either stuck at a barrier or freely moving in the bulk oil. This creates high-field regions, prone to PD activities. Different power equipment operates at different voltages such as AC, DC, square voltage, pulse voltage, fast-rise transient voltage etc. This study presents the influence of sinusoidal voltage, slow- and fast-rise square voltage on PDs in two different geometries using optical PD measurement technique. Fast-rise square voltage has the lowest PD inception voltage while the sinusoidal voltage has the highest. This is may be due to the influence of homo- and hetero-charges. Fast-rise square voltage displayed higher PD magnitude at inception which may be connected to the rise time of the voltage.

For high-voltage (HV) AC cable transmission systems, the metal sheaths of three separate single-core cables are cross-bonded at each end of the cable section, to suppress the induced voltages in sheaths. The status of HV cable grounding systems is, therefore, an important consideration for power utilities. This study presents the status evaluations of 93 cable grounding systems in Beijing, obtained using the standards established by State Grid Corporation of China. As a result, 13 of these systems were classified as abnormal or defective. Additionally, a theoretical calculation of grounding currents was proposed and these 13 systems are re-evaluated by comparing the calculated and measured values of certain parameters. Based on this work, the authors propose a modified evaluation standards. It is indicated that the absolute value of grounding current (|I|) during a given 24-hr period has no relationship with the status of grounding system, and the ratio of grounding current to load current (K) at the time of maximum load current could be used as a status indicator instead of K at some other time, in order to avoid possible incorrect evaluations due to light load conditions.

Measuring acoustic emission (AE) of partial discharge (PD) phenomena can be adopted to estimate the condition of power transformers. However, the environmental noise encountered with AE of PD measurements negatively affects the accuracy of PD localisation and classification. Thus, efficient signal denoising techniques are required for noise suppression and hence, better detection accuracy. This study deals with white noise and it is a continuation of a previously published work that deals with random noise. The published work addresses the random noise suppression using a method named, power spectral subtraction denoising (PSSD). This study applies PSSD to the PD signals contaminated with white noise and uses a novel scheme of noise power spectrum density estimation. Multiple types of AE signals are examined including signals produced by corona, surface, parallel, and void PDs. Synthetic and real data demonstrate the superiority of the proposed method over the wavelet shrinkage denoising method as it can more effectively eliminate white noise and preserve signals of low signal-to-noise ratio.

Non-pressurised air is extensively used as basic insulation medium in high-voltage equipment. Unfortunately, an inherent property of air-insulated design is that the system tends to become physically large. On the other hand, the application of dielectric barriers can increase the breakdown voltage and therefore decrease the size of the equipment. In this study, the impact of dielectric barriers on breakdown voltage enhancement is investigated under both direct current (dc) and alternating current (ac) applied voltages. For this purpose, three kinds of dielectric barriers in two different high-voltage electrode structures are investigated. In the first structure, several experiments are carried out with four different electrode arrangements, keeping the inter-electrode gap constant while varying the position of the dielectric barrier between the electrodes. In the second structure, the inter-electrode gap is varied while the high-voltage electrode is covered with dielectric materials. The influences of different parameters such as inter-electrode spacing, electric field non-uniformity factor, and dielectric materials on the breakdown voltage are investigated for applied 50 Hz ac and dc voltages. In addition, a simulation model to approximately calculate the breakdown voltage is proposed and validated with the experimental results.

With the advent of non-thermal plasma technique for diesel exhaust treatment attention is being focused on reducing oxides of nitrogen (NO _x ) both from stationary as well as automobile sources. In this work, an attempt has been made to enhance NO _x reduction only by utilising a plasma/ozone injection approach without resorting to additional treatments based on catalysts/adsorbents. It was observed that cascading ozone injection with discharge plasma enhances the reduction of NO _x as high as 95% for the specific energy of 123 J/l. In the long run, this plasma-only based approach may be beneficial or a possible alternative for catalyst/adsorbent based NO _x treatments. The results have been discussed and a comparative analysis has been made with respect to individual plasma and ozone injection treatment.

Due to excellent anti-pollution flashover performance, a composite insulator has become the most frequently and widely used insulator product in transmission lines. Sheath hydrophobicity is the core factor that determines the anti-pollution flashover performance of the composite insulator. To study the change rule of insulator sheath hydrophobicity under the long-term operation condition, more than 390 samples produced by the same manufacturer that had operated for 3–22 years were extracted from the adjacent lines to eliminate the impact of the running environment and manufacturer formula. To study the reasons for hydrophobic fluctuations, surface energy tests and Fourier transform infrared spectroscopy tests were conducted on the superficial layer materials based on a two-droplet method. The change rule of the material physical and chemical properties with operation time was obtained. Next, the relationship between the surface microstructure of the material and operation time was determined by laser scanning confocal microscopy and scanning electron microscopy. Finally, based on the analysis results of surface energy and surface topography, the physical model of shed material hydrophobic variation in the operation process was obtained.

The distortion of the electric field in the oil–pressboard composite insulation caused by the accumulation of the interface charge is detrimental to both the insulation design and operation of converter transformers. The influence of moisture content on the surface charge accumulation of oil–pressboard insulation under DC voltage was studied in this study. In accordance with the Kerr electro-optic effect, the electric field strengths in transformer oil and the surface charge density were acquired after applying the positive and negative DC voltages in three oil–pressboard insulation models with different moisture content, respectively. The resistivities of the oil and pressboard in three models, namely Model 1# with 3.8–4.2 ppm moisture in oil and 0.35–0.37% moisture in pressboard, Model 2# with 7.6–7.9 ppm moisture in oil and 0.79–0.82% moisture in pressboard and Model 3# with 14.9–15.4 ppm moisture in oil and 1.39–1.42% moisture in pressboard, was also measured. The results indicate that: (i) as negative charges in oil accumulated on the pressboard surface in a much greater speed than the positive ones, the electric field in transformer oil under negative DC voltage decreases more rapidly with time than that under positive DC voltage; (ii) the increase of the moisture content in both oil and pressboard, under either positive or negative DC voltage, leads to the decrease of both the electric field strength in transformer oil and the charge density with time; and (iii) the increase of moisture content could not only decrease the resistivity of both oil and pressboard, but also the ratio of the resistivity between the pressboard and the oil. On the basis of the Maxwell–Wagner theory, the decrease of the ratio between the pressboard and oil could lead to the decrease of the interfacial charge density, leading to the slow transient process of the electric field in transformer oil under DC voltage.