Combined modulus and impedance spectra are widely employed to explore electrical inhomogeneity and carriers' behaviors in dielectric ceramics based on equivalent circuit. However, discrepancies are found between practical dielectric responses and widely proposed equivalent circuits. Taking ZnO varistor ceramics as an example, a low-frequency dielectric relaxation, which can be detected in practical dielectric spectroscopy, is overlooked in simulated dielectric spectroscopy based on the proposed equivalent circuit according to modulus and impedance spectra. Therefore, equivalent circuits are frequently incomplete because the real low-frequency dielectric response is unable to be characterized from them. The problem originates from debatable understanding of frequency responses in modulus and impedance spectra. The low-frequency peak in modulus spectroscopy is proved originating from DC conductance instead of a real dielectric relaxation and the involvement of DC conductance component makes a low-frequency dielectric relaxation unable to be characterized in modulus spectroscopy. Therefore, improved dielectric spectroscopy eliminating the component of DC conductance is proposed and a clear peak corresponding to the low-frequency dielectric relaxation appears. In addition, a modified equivalent circuit which is in accordance with practical dielectric responses in not only modulus and impedance spectra but also dielectric spectroscopy is presented.

Environmental protection is the future trend of power equipment development, and is also a research hotspot in the field of power cable insulation in recent years. Due to the excellent electrical properties and recyclability, polypropylene (PP) based composites are regarded as promising insulating materials for eco‐friendly next‐generation power cables. However, the high modulus and hardness of pure PP make it difficult to be directly employed as cable insulations, which needs to be further optimised. General methods of mechanical performance regulation often result in the deterioration of electrical performance, such as breakdown strength, space charge and so on. Therefore, it is recognised that the major challenge impeding practical applications of PP power cable insulation arises from the synergetic regulation of multi‐performances. The multi‐level structures influencing the multi‐performances of PP are introduced by the authors and the researches on the performance enhancement of PP through nanoscale structure regulation in recent years are reviewed in detail. Seven kinds of modification methods including nano‐doping, chemical grafting, in‐suit copolymerisation, heat treatment, nucleating agent, voltage stabiliser and elastomer blending are paid special attention. Based on the full understanding of the research status, the challenges and issues of future research are put forward for eco‐friendly PP power cable insulation.

A low frequency dielectric relaxation process of CaCu₃Ti₄O₁₂ ceramics, which is generally overlapped by dc conduction in traditional dielectric spectra, is detected and clarified based on an improved analytical methodology in this letter. This relaxation process remarkably contributes to instability of low frequency permittivity and it clearly demonstrates the correlation between charge migration and space charge polarization. It is revealed that conduction will be achieved if carriers migrate and combine in the electrodes, while space charge polarization will be achieved if carriers migrate to the electrodes without combination.