Nanodielectrics, which are concentrated in polymer matrix incorporating nanofillers, have received considerable attention due to their potential benefits as dielectrics. In this paper, short-term breakdown and long-term failure properties of nanodielectrics have been reviewed. The characteristics of polymer matrix, types of nanoparticle and its content, and waveforms of the applied voltage are fully evaluated. In order to effectively comment on the published experimental data, a ratio k has been proposed to compare the electric properties of the nanodielectrics with the matrix and assess the effect for nanoparticles doping. There is evidence that the short-term breakdown properties of nanodielectrics show a strong dependence on the applied voltage waveforms. The polarity and the cohesive energy density (CED) of polymer matrix have a dramatic influence on the properties of nanodielectrics. Nanoparticle doped composites show a positive effect on the long-term failure properties, such as ageing resistance and partial discharge (PD) properties of nanocomposites are superior than microcomposites and the matrix. The larger the dielectric constant and CED of the matrix become, the more significant improvements in long-term performance appear. Based on the reported experimental results, we also present our understandings and propose some suggestions for further work.

To ensure the power system operates safely and reliably, it is essential to monitor and evaluate the health condition of power equipment on‐line or off‐line. This study reviews the research status in condition monitoring and diagnosis of power equipment, including transformer, gas insulated switchgear, cable, external insulation, generator, and power capacitor in recent years. Although much progress has been made in technologies of condition monitoring and fault diagnosis such as test accuracy, fast and accurate fault localisation and recognition of fault types, there are still many deficiencies which needs further research work, including the reliability of signal collection from sensors, the accuracy of data treatment and analysis, anti‐interference performance of test equipment, appropriate models used for condition evaluation. The prospective of condition monitoring and diagnosis technologies of power equipment are also presented in this study. It is proposed that the application of big data, internet of things and cloud computing should be expected and given special attention in the near future.

The performance of electrical equipment and devices is determined to a great extent by the properties of their insulating materials. In power systems and electrical devices, insulating materials have to work in extreme circumstances that can include high temperature differences, intense radiation, and strong electric fields. Such conditions demand high‐quality insulating materials with superior electrical, thermal, and mechanical properties as well as resilience to other environmental stresses. This study focuses on advances in insulating materials since the early 20th century and reviews the many developments in their properties and applications, including electric breakdown strength, thermal conductivity, temperature resistance, corona resistance, and specific energy storage in dielectrics. Some research progress on other properties is also covered, such as non‐linearity and radiation resistance. Investigations into the properties of insulating materials can greatly assist in understanding their interface effects and composite structures, which in turn is helpful for discovering methods to improve the performance of electrical devices. Future directions for research are proposed to guide new investigations and support the development of even better insulating materials.