Study On Switching Reignition Overvoltage Of Vacuum Circuit Breaker In Offshore Wind Farms

The world's major economies have successively proposed ambitious carbon neutral goals,and the development of offshore wind farm(OWF)is in full swing.Reignition may occur when switching vacuum circuit breaker(VCB).The sudden chopping and reignition of the arc between the contacts cause the mutual conversion of electromagnetic energy between the inductance and capacitance elements in the system,causing voltage oscillation.The reignition overvoltage has high amplitude and steepness,which may cause serious harm to the insulation of power equipment including the terminal transformer.Therefore,it is necessary to conduct research and select appropriate suppression measures.The main work of this paper is as follows:(1)The paper considers the chopping current of the VCB,dielectric strength,highfrequency(HF)arc quenching ability and arcing voltage,and writes a program to control the arcing time,then a user-defined model that can reflect the reignition characteristics of VCB in PSCAD/EMTDC is established.At the same time,based on the transmission line theory,the horizontal and vertical grounding system models considering their frequency characteristics are constructed.The frequency-dependent(phase)model is used to model the submarine cable,stray capacitance is added at the transformer port to show its HF characteristics,and HF models of doubly-fed wind turbines and arresters are established.(2)The simulated OWF experimental platform is used to carry out the VCB switching inductive load experiment.The voltage and current waveforms of the reignition process are measured to obtain the actual 40.5 kV VCB parameters.Also,the simulation experiment under the same conditions in PSCAD/EMTDC is conducted.Compared with the experimental waveform,the validity of the constructed HF model is verified.(3)A simplified simulation of an OWF with single feeder was constructed in PSCAD/EMTC.The traditional value and recommended value based on experiment of the dielectric strength of VCBs was simulated to study the influence of different characteristics to the amplitude and steepness of the overvoltage.At the same time,the effects of static and HF models of the grounding system and the effects of different ground resistance related to the depth of sea water on the reignition process are compared.Finally,based on actual arrester types,the suppression effect of different wiring methods of the arresters on the phase-to-ground overvoltage,phase-to-phase overvoltage and steepness of overvoltage are simulated.