查看更多>>摘要：Polypropylene(PP)-based recyclable materials have attracted tremendous interest for HVDC cable insulation applica-tions due to their superior electrical properties,e.g.,high thermal stability and superior recyclability.Compared with crosslinked polyethylene(XLPE),PP-based materials exhibit the advantages of not only higher working temperatures but also facile and efficient cable manufacturing with reduced costs,which are highly desirable in HVDC cable manufacturing.Considering their promising advantages,PP-based materials have received significant attention from both academia and industry in the field of HVDC cable insulation.In order to adopt PP as a cable insulation material,the mechanical flexibility of PP should be improved.However,regulations of the mechanical properties inevitably influences the electrical properties of PP.So extensive research has been conducted on the regulation of the mechanical and electrical properties of PP.This review summarizes the research progress on recyclable PP-based materials for HVDC cable insulation applications.Particular attention is placed on the electrical property regulations and material structure-property relationships.The challenges that remain to be addressed and the opportunities for future studies on PP-based recyclable HVDC cable insulation materials are also presented.
查看更多>>摘要：Modular multilevel converter(MMC)is increasingly being applied to high voltage direct current(HVDC)systems.However,dc short circuit situations restrain the application of a conventional half bridge MMC system.In this paper,a new sub-module topology with inserted thyristor can help the MMC system clear a dc side fault.Working states and devices voltage stress of the proposed topology are analyzed and the conduction loss comparison between the proposed topology with several existing topologies with dc fault blocking capability is carried out.Results show the proposed topology is superior to other topologies in terms of conduction loss while using the same voltage rating devices.Besides,compared with traditional half bridge topology,only thyristors and diodes are added in the proposed topology.Therefore,cost of the proposed topology can be lower than conventional hybrid MMC sub-modules.At last,the fault blocking capability of the proposed topology is verified in the simulation.
查看更多>>摘要：The deterioration of winding defects is one of the important causes of power transformer fires and even explosion failures.The change of leakage magnetic field distribution is the most direct response to winding defects.Currently there are few sensors suitable for online measurement of the internal magnetic field of transformers.Based on the Faraday magneto-optical effect,a magnetic field sensor with wide range and high sensitivity is proposed in this paper,which is suitable for the interior use of transformers.The straight-through optical structure with interior polarizer is adopted,and the sensor has a measurement range of 1.5 T and a sensitivity of 1 mT.It also possesses a small size,with a length of about 30 mm after encapsulation.The influence mechanism of vibration and temperature is revealed through theoretical analysis and numerical simulation.It is proposed to filter out the interference of vibration by characteristic frequency analysis and to compensate for temperature by a two-probe structure.An anti-interference test verifies the effectiveness of this method,and it can reduce the error from 80.56％to 2.63％under the combined interference of vibration and temperature.
查看更多>>摘要：UHV transmission lines are usually equipped with high-voltage shunt reactors.These reactors and the resulting degree of compensation affect the voltage,current,and other electrical characteristics of secondary arcs.In this paper,a low-voltage experimental simulation setup to produce secondary arcs in different compensation modes is established,and the morphological and electrical characteristics of recorded arc images and discharge waveforms are analyzed.For morphological characteristics,the degree of secondary arcs is compared for different compensation modes.For electrical characteristics,the arc waveform,volt-current characteristics,and zero-current time of secondary arcs are compared for different compensation modes.These results provide a foundation to determine the time of extinction of secondary arcs on overhead lines in the case of compensation,as well as technical support to develop effective arc suppression and extinction techniques.
查看更多>>摘要：The cluster DC voltage balancing control adopting zero-sequence voltage injection is appropriate for the star-connected cascaded H-bridge STATCOM because no zero-sequence currents are generated in the three-phase three-wire system.However,as the zero-sequence voltage is expressed in trigonometric form,traditional control methods involve many complicated operations,such as the square-root,trigonometric operations,and inverse tangent operations.To simplify cluster voltage balancing control,this paper converts the zero-sequence voltage to the dq frame in a DC representation by introducing a virtually orthogonal variable,and the DC components of the zero-sequence voltage in the dq frame are regulated linearly by proportional integral regulators,rather than being calculated from uneven active powers in traditional controls.This removes all complicated operations.Finally,this paper presents simulation and experimental results for a 400 V/±7.5 kvar star-connected STATCOM,in balanced and unbalanced scenarios,thereby verifying the effectiveness of the proposed control.
查看更多>>摘要：A centralized framework-based data-driven frame-work for active distribution system state estimation(DSSE)has been widely leveraged.However,it is challenged by potential data privacy breaches due to the aggregation of raw measure-ment data in a data center.A personalized federated learning-based DSSE method(PFL-DSSE)is proposed in a decentralized training framework for DSSE.Experimental validation confirms that PFL-DSSE can effectively and efficiently maintain data confidentiality and enhance estimation accuracy.
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