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.

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Surface tracking has been one of the challenges for outdoor organic insulations, in electronic and electrical devices. In this paper, surface tracking behavior of nano-MgO/epoxy composite samples were measured according to the standard IEC 60112. Improved tracking resistance was obtained in nanocomposites with an 18.75% uplift in the comparative tracking index, and a decrease of 58.20% in the surface ablation area at a fixed 425 V. It was observed that the tracking resistance and surface hydrophobicity shared the same tendency—both, the comparative tracking index and surface contact angle increased with an increase of the nanofiller content. Samples with better hydrophobicity exhibited a higher tracking resistance. It could be the case that the conductive pathway of contamination was harder to form, as a result there were fewer discharging processes. With the development of surface tracking, the surface contact angle abruptly decreased, at first, and tended to be constant, which was also accomplished with the failure of samples. In addition, reduced surface resistivity was also found in the nanocomposites, which was beneficial for releasing surface charges and inhibiting distortions in the electric fields.

Space charge accumulation is the main factor in accelerating the degradation of polymeric insulation in high-voltage direct current (HVDC) cables. It is essential for the development of HVDC cables to suppress the space charge in the insulating layer. In this paper, an approach is presented to decrease carrier injection from the inner semiconductive layer to the insulating layer, using a magnetic semiconductive compound. The semiconductive shielding compound was prepared by adding strontium ferrite to a carbon black/ethylene-vinyl acetate/low-density polyethylene (LDPE) matrix. The addition of strontium ferrite led to an increase in the residual magnetic induction of the semiconductor shielding layer. Unmagnetized and magnetized semiconductive compounds were used as electrodes to test the injection of carriers into the LDPE insulation layer. When SrFe12O19 had been added, the charge injected into the LDPE by the magnetized semiconductive layer was less than with an unmagnetized semiconductive layer. When the content of SrFe12O19 was 5 wt. %, 10 wt. %, 30 wt. %, and 50 wt. % in the semiconductive compound, the charge in the LDPE was reduced by 4.2%, 8.1%, 12.5%, and 27.1%, respectively.

The accumulation of space charge is considered to be an important key factor to accelerate the aging of the insulation of HVDC cables. How to reduce the accumulation of space charge in the insulation layer is an urgent problem to improve the voltage level of cables. In this paper, an approach is presented to prevent charge from the inner semiconductive layer to the insulating layer, using a modified semiconductive compound by doping magnetic carbon nanofibers. Through microwave-assisted heating, Ni was deposited on the surface of carbon nanofibers which have been pre-treated. Modified semiconductive compound electrodes was used to test the injection of charges. The results showed that charge injected into LDPE insulting layerwith modified CNFs-Ni/ LDPE electrode is less than that with LDPE semiconductive layer without CNFs-Ni electrode.

In the multi-output high-voltage isolated power supply for solid-state switches, LCL resonant network is used to obtain the constant current source on the bus, and the bus current is independent of the load. Therefore, the secondary side of the toroidal transformer needs to use the current input voltage regulator circuit. When the input is a current source instead of a voltage source, the traditional voltage regulator circuit is no longer applicable. Therefore, this paper focuses on the study of dc voltage regulated circuit with current source input. Compared with the traditional linear regulated power supply, switching power supply has the advantages of high efficiency, large output power, small size, light weight and low cost. In this paper, pulse width modulation (PWM) technology is used to control the switching on and off, and UC3843 is used to design a switch type regulated power supply with small size, simple circuit, adjustable output and over voltage protection function. Tina-TI software was used for simulation analysis, and the main circuit and control circuit were built. The current source of 1.25A and 40kHz output by the secondary side of the toroidal transformer is converted into a stable 10V DC voltage source, which verified the correctness of the design. Tina-TI software can be used to analyze and design power supply with different requirements, improve power efficiency, reduce design complexity, and thus shorten development cycles.

A LCL-based resonant converter is shown to behave as a constant-current source when operated at resonant frequency in this paper. This paper focuses on the realization of zero voltage switching (ZVS) in the case of constant-current in LCL resonant converter and how to reduce the influence of high harmonics on the output current. First, the principle of LCL resonant converter as a constant-current source is described. Second, when the switching frequency of the converter deviates from the resonant frequency point, the current gain curves corresponding to different quality factor Q and the boundary curves realizing ZVS turn-on are analyzed. Third, the influence of the ratio (m) of resonant inductors on the output current of the converter and ZVS turn-on is analyzed, and the value of m is determined. Finally, Pexprt software was used to design the magnetic component model, and combined with Simplorer software for combined-simulation. A simulation circuit model with output 80W/0.32A was designed and experimental results are presented. The correctness of the theoretical analysis has been verified.

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