Research and application of a power-flow-calculation method in multiterminal VSC-HVDC power grid

For demonstrating a multiterminal voltage-source converter(VSC)-based high-voltage DC(HVDC)(VSCHVDC) project, this study puts forward a technical route for calculating the power flow in a 500-kV VSC-HVDC power grid in comparison with that of an AC power grid. The Jacobian matrix used in the power-flow calculation was deduced through methods such as Newton–Laphson iteration and Taylor series expansion. Further, the operation effect of powerflow calculation on a true bipolar VSC-HVDC power grid was analyzed briefly. The elements of the Jacobian matrix corresponding to VSC were studied under the mode of droop control and the control strategy of VSC-HVDC power grid was analyzed in detail. The power-flow calculation model for VSC-HVDC power grid of the master–slave control mode was simplified using the PQ decomposition method of the power-flow calculation of an AC power grid. Moreover, a four-terminal model of the Zhangbei VSC-HVDC demonstration project was established and tested on MATLAB. The simulation results under two kinds of operating conditions were analyzed and compared to the results of BPA; the deviation between the power-flow results was studied. The results show that the proposed calculation method can provide a feasible support for calculating the power flow in VSC-HVDC grids.

Dielectric response--A nondestructive approach to probing the micro‐interface of aluminium hydroxide filled silicone rubber composites for outdoor insulation

Composite polymer dielectrics have strong electrical,mechanical,thermal and environmental properties but experience both high electric fields and harsh environmental conditions as outdoor insulation.The present investigation of the stress-strain characteristics and morphology of the fracture cross-section reveal the risk of a weakly bonded interface between the aluminium hydroxide(ATH)filler and silicone rubber used for insulators in transmission lines and substations.Dielectric response measurements are proposed as a non-destructive probe of the interface quality.An analysis,based on the Dissado–Hill model,indicated that the introduction of ATH interfaces gave rise to a quasi-DC process,in which charge transport is in the form of hopping along the weakly bonded interfaces.A schematic plan is proposed that would allow such an analysis to be used to obtain quantitative information correlated to the status of the weakly bonded interface for the diagnosis of micro-interface quality in ATH-filled silicone rubber and dielectric composites in general.

Non-destructive thermal ageing evaluation of P(VDF-HFP)film based on broadband dielectric response

Capacitors and sensors based on polymer dielectric materials are key components in electrical systems and electronic devices.Considering the temperature rise during operation,an effective evaluation method for the thermal ageing of polymer matrix is urgently needed.P(VDF-HFP)film with a thickness of 20μm is manufactured by solution casting and a thermal ageing experiment up to 1000 h is conducted.Dielectric responses of wide ranges of temperatures and frequencies are measured for samples with different ageing durations.The universal relaxation law and Dissado–Hill dielectric response model are applied to further investigate the results.The characteristics of individual processes are obtained,which demonstrate that the main chain relaxation following the Vogel−Fulcher−Tammann equation and side chain relaxation following the Arrhenius equation both remain unchanged after thermal ageing.However,the activation energies of those two processes change significantly during the process and show different variation trends.The activation energy of the side chain relaxation gets larger monotonically due to the influence of annealing and the breaking of crystalline region.As a result,a non-destructive evaluation method for the thermal ageing of P(VDF-HFP)is proposed accordingly.

Failure analysis of a field brittle fracture composite insulator:characterisation by Xray photoelectron spectroscopy analysis

In the present work,a field brittle fracture composite insulator was collected and examined with the purpose of obtaining a better understanding of the failure features.Firstly,the macroscopic and microscopic fractography of this fractured composite insulator was observed confirming that the classical brittle fracture morphology features appeared in this field failed composite insulator.Secondly,the X-ray photoelectron spectroscopy(XPS)analysis was performed on the fracture surface of the glass-fibre-reinforced polymer rod.By examining the XPS survey spectra and high-resolution XPS spectra for nitrogen,sulphur,silicon,calcium,aluminium,boron and carbon elements,the type of the glass fibre and the acid source responsible for this brittle fracture composite insulator were confirmed.Furthermore,the oxidation of the silicate network of glass fibre at the fracture surface was first observed,meanwhile,the oxidation of the epoxy resin matrix was also observed.The leaching of non-silicate constituents leading to a high-silica glass fibre was also observed;moreover,in comparison with the calcium and aluminium elements,the boron element resides in the silicate network was more preferential to be leached.The present work provides an insight into the brittle fracture in high voltage composite insulator from chemical properties point of view.