The Study On DC Magnetic Bias Of Receiving End In Xiluodu～Zhejiang HDVC Project

HVDC transmission technology develop rapidly in in our country for its advantages of long transmission distance, large transmission capacity and small transmission loss. But it will also bring many adverse effects to the original AC power grid. When the DC transmission lines are in monopole ground return operation mode at the period of debugging and maintenance or fault, DC current will flow from the neutral grounding point of the transformer into windings, leading to the normal operation transformer generating DC magnetic bias, transformer losses increase, noise increase, and serious vibration, which brings serious harm to the transformer itself and the safe and stable operation of the AC grid.Taking the DC magnetic bias of the power receiving grid end of Zhejiang west Xiluodu Zuoan UHVDC transmission project which is in operation as the research object, the theory has carried on research and discussion from the following aspects. Firstly, the development of UHVDC technology and Xi Zhe UHVDC transmission project are introduced, the causesof DC magnetic bias and influences to the transformer even the whole grid are expounded, and research status at home and abroad are discussed. Secondly, a unipolar debugging scheme of Xi Zhe DC project is proposed, operation parameters of the receiving end grid AC transfonners are measured, influences of grounding current vibration to the iron core and clamp, and noise of measured data are analyzed, the calculation of soil resistivity in the field measurement and Simulation of the bias current impact potential distribution and flow through transformer neutral point of the DC. Thirdly, the measures to curb the neutral point of transformer DC magnetic bias current, the operating principle of the series resistance method, series capacitor method, and reverse current compensation method for the DC suppression measures are studied, and the practicability and validity of the comprehensive evaluation, obtained the partial magnetic suitable for Zhe Xi UHVDC project by the end of the grid suppression measures. Finally, the work principle, device isolation straight after a detailed introduction of the PAC-50K capacitor related technical parameters, operation and control strategy on the basis of analysis of the capacitance across the device, direct influence on substation short-circuit current level, control and protection devices and the neutral reactor, the technical scheme of Western Zhejiang Power Grid with 500000 volts transformer substation capacitor blocking device is put forward.