Research On The Influence And Restraining Measures Of Grounding Dc Current Of "Hu-Liao HVDC" On The Transformers In Anshan Power Grid

In our country,along with the general policy "West to east power transmission,North-south power exchange and the Nationwide interconnection",the High Voltage Direct Current(HVDC) transmission technology is applied more and more abroad in long distance,bulk power transmissions,because of the characteristic,such as the big Capability,the little wastage and unlimited transportation by stabilization.But the HVDC transmission system maybe operated in ground return status when the system is in debug or failure, great current flowing into earth through grounding electrode,resulted in the potential of earth increasing.The grounding DC current flows through the main transformers in the AC system will cause DC bias magnetic saturation,resulting in excitation current distortion, noises and vibration increase,overheat,producing harmonics,reactive changes,which will affect the safe operation of the main transformers and the power system.Therefore,it is necessary and important to research the DC bias of main tansformer.This dissertation aims to have a primary probe into questions mentioned above,the main reasons and basic theory of DC bias to transformer is introduced;combining with the DC current values measured at the tansformer neutrals,the influence of DC bias to the main transformers in the "anshan" power grid is analyzed;the merits and demerits of three restraining measures to the DC bias of transformer is compared,such as connecting DC-isolation capacitor in series with the neutral, current restriction by adding small resistance to the neutral, injecting reverse DC current into the neutral;the measure of connecting DC-isolation capacitor in series with the neutral and current restriction by adding small resistance to the neutral is studied further,recommended a scheme to restrain the DC bias to the main transformers in the "anshan" power grid according to the results of study.