In the series hybrid active power filter (SHAPF) based on fundamental magnetic flux compensation (FMFC), the harmonic voltage across the magnetising inductance of the series transformer will disturb the inverter output current and worsen the filtering effect of the SHAPF. However, this influence caused by harmonic voltage was ignored in the previous research. Therefore there is blindness and casualness in the parameter selection of the SHAPF based on FMFC. Taking a 10 kV, 1 MVA industrial application of the SHAPF in a manufacture factory in Guangdong Province as an example, this study establishes the accurate global mathematical model of the SHAPF. Furthermore, based on the proposed global mathematical model, the series transformer parameters are analysed in detail to show its influence on the filtering performance of the SHAPF. This mathematical model can be used as foundations of the parameter selection of the SHAPF. Finally, an engineering prototype is manufactured and applied. The practical experimental results verify the theoretical analysis.

The interface pressure between the cable attachment and the body is crucial for the stable long-term operation of the cable. To solve the issue of interface insulation characteristics’ damage caused by the pressure transducer measurement method, a non-destructive testing method of silicone rubber interface pressure using nonlinear ultrasound is presented. Initially, the study analyzes the propagation characteristics of ultrasonic waves at the interface of cross-linked polyethylene and silicone rubber. The study also establishes the relationship between the nonlinear coefficient and the interface pressure. Subsequently, a nonlinear ultrasonic test platform is constructed using the pulse reflection method to measure the interface pressure of flat silicone rubber and cross-linked polyethylene through nonlinear ultrasonic testing. Theoretical and experimental results indicate that the fundamental amplitude of the frequency domain of the interface reflection wave decreases, and the second harmonic amplitude and nonlinear coefficient both increase as pressure increases. These results demonstrate that the nonlinear ultrasound, non-destructive testing method can accurately evaluate the interfacial pressure state of the cable accessories.

In this article, a novel DC voltage control strategy which is independent of the detection of the primary winding voltage across the series transformer is proposed to solve the DC voltage control problem of the series hybrid active power filter (APF). Meanwhile, this proposed DC voltage control method adopts an open-loop control strategy. The inverter generates unchanged DC voltage control current to ensure that the fundamental voltage loss of the series transformer remain stable. The simulation and experimental results validity and feasibility of the proposed DC voltage control the method of the series hybrid APF.