High‐temperature dielectric materials for capacitive energy storage are in urgent demand for modern power electronic and electrical systems. However, the drastically degraded energy storage capabilities owing to the inevitable conduction loss severely limit the utility of dielectric polymers at elevated temperatures. Herein, a new approach based on the in situ preparation of oxides onto polyimide (PI) films to high‐temperature laminated polymer dielectrics is described. As confirmed by computational simulations, the charge injection at the electrode/dielectric interface and electrical conduction in dielectric films are substantially depressed via engineering the in situ prepared oxide layer in the laminated composites. Consequently, ultrahigh dielectric energy densities and high efficiencies are simultaneously achieved at elevated temperatures. Especially, an excellent energy density of 1.59 J cm−3 at a charge–discharge efficiency of above 90% has been achieved at 200 °C, outperforming the current dielectric polymers and composites. Together with its excellent discharging capability and cyclic reliability, the laminate‐structured film is demonstrated to be a promising class of polymer dielectrics for high‐power energy storage capacitors operating at elevated temperatures. The facile preparation method reported herein is readily adaptable to a variety of polymer thin films for energy applications under extreme environments.
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ABSTRACT
This position paper, prepared by the IEEE DEIS HVDC Cable Systems TechnicalCommittee, illustrates a protocol recommended for the measurement of space charges in full-size HVDC extruded cables during load cycle qualification tests (either prequalification load cycles or type test load cycles). The protocol accounts for the experimental practices of space charge measurements in the thick insulation of coaxial cables in terms of poling time, depolarization time, heating and cooling of specimens, as well as for the experience gained very recently from such kind of measurements performed in the framework of qualification tests relevant to ongoing HVDC cable system projects. The goal of the protocol is not checking the compliance with any maximum acceptable limit of either space charge or electric field. Rather, this protocol aims at assessing the variation of the electric field profile in the cable insulation wall during poling time at the beginning and at the end of load cycle qualification tests for full-size HVDC extruded cables. Indeed, in the design stage the electric field distributions are determined by the cable geometry and by temperature gradient in the insulation. Thus, the design is based on macroscopic parameters conductivity and permittivity and how they depend upon temperature. Any disturbance of the electric field due to space charge accumulation will only be revealed during space charge measurements either in as-manufactured state or in the aged state after load cycle qualification tests.
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