Research On DC Bias Mitigation Strategy Based On The UHVAC Transmission Projects

With the rapid development of UHVDC and UHVAC transmissioninChina,DC magnetic bias of UHVAC transformers is paid more and more attention to,when the UHVDC transmission system works in mono-polar operation.It will make partial overheating,vibration and increasing noise of transformers,which will threaten the operation security of UHVAC transformers.Althoughtransformers can endure a small DC bias current,there is no unified standard to value it.Manytransformer manufactures can’t provide their allowable DC value of transformers.The paper hasanalyzed the value and concluded a list focus on the transformers in East China power grid.The value is also an aim of restraining DC bias current.Unfortunately,there is no possibility to solve all the problems caused by HVDC transmission’s earth-return current on AC power grid based on HVDCtransmission.Considering the characteristics of UHVAC transmission,it is important andnecessary to have a research on DC bias mitigation strategy based on the UHVAC transmission projects.Based on resent 1000 kV Liantang(Huxi)UHVAC transmission project and 1000 kV Zhebei-Fuzhou UHVAC transmission project,two strategies were compared.UHVAC transformer grounding viaresistance DC limiting device or capacitor DC blocking device is an efficient way to solve DC bias problem.According to the restricted inobjectiveconditions,the paper has drawn some conclusions in choosing the DC Bias mitigation strategy.