Economy Analysis of Flexible LCC-HVDC Systems with Controllable Capacitors

Commutation failure(CF)is a frequent dynamic event at inverter of LCC-HVDC systems caused by AC side faults which can lead to inverter blocking,interruption of active power transfer,and even system blackout.To eliminate CFs and improve system performance,new Flexible LCC-HVDC topologies have been proposed in previous research but with limited analysis on its economic performance.Therefore,to further validate the applicability of Flexible LCC-HVDC topologies,this paper utilizes Life-Cycle Cost Analysis model to analyze the life-cycle cost of inverter stations for conventional LCCHVDC,Capacitor Commutated Converter based HVDC(CCCHVDC)topology and Flexible LCC-HVDC topologies including Controllable Capacitor based Flexible LCC-HVDC,AC Filterless Controllable Capacitor based Flexible LCC-HVDC and improved Flexible LCC-HVDC.Through a case study based on a 500 kV,1000 MW LCC-HVDC scheme,comparison results show that the AC Filterless Controllable Capacitor based Flexible LCCHVDC topology and the improved Flexible LCC-HVDC topology have lower cost than the conventional LCC-HVDC and CCCHVDC topologies,which proves that the elimination of CFs can be achieved with reduced cost.

Equipotential shielding voltage sensor for contact measurement of transient voltage in EHV/UHV power grids

In this study,an equipotential shielding voltage sensor is proposed to achieve contact measurement of transient voltage in extra-high voltage(EHV)/ultra-high voltage(UHV)power grids.Two design versions of the voltage sensor for engineering application are described.One version of the sensor is designed as a miniaturized sensor for non-dis-turbing measurement of potential distribution along power electronic equipment under transient voltage.The other version is designed for online measurement and monitoring in alternating current EHV/UHV power grids.Based on the design parameters,the performance of the sensor is evaluated,including stability of measurement,shielding effect against the interference from adjacent objects and frequency bandwidth.In order to verify the performance of this sensor,an experimental comparison between this sensor and a standard capacitive voltage divider used in high voltage laboratory was carried out and the results of comparison are presented.The results show that the difference of measured peak voltage between the two devices is no more than±5%,and the difference of measured time parameters between the two devices is no more than±15%.