The Application Reaserch On DC Bias Suppression Devices For 220KV Transformer

With the development of power electronics technology, HVDC(High Voltage Direct Current) has played an important role in long-distance and high-capacity transmission and interconnection of regional power system. HVDC monopole to groud operation will cause DC bias which is generated by DC current in the neutral point grounded transformer. DC bias will cause rapid increase of transformer excitation current and result in overheat, noises.It might even cause the damage of transformer and Capacitor banks, which will threaten the safety of the grid.The mechanism of DC bias and the expression of flux in the transformer after the DC bias has been discussed in this paper, which also analyzed the relationship of the DC current and other variable under HVDC monopole to groud operation. On the base of compared with the suppression of DC bias at home and abroad and analyzed the influence of monopole operation in Yangchun 220 KV AC system, Capacitance DC-blocking device of DCBD-CⅡ bases on the protection of parallel thyristor has proposed. Compared to the general blocking capacitor device, it does not require extra thyristor to cut off the loop, The topology of the main circuit can be a lot of simplification, reducing the cost of the device, while the pure hardware integrated circuit protection and computer protection dievice fully dual redundant, improveing the reliability and intelligence of the system.220kV Linxiao station as an example, this paper has introduced the installation, testing and commissioning process of the blocking device, routine maintenance and daily processing apparatus as well. During the period of DC monopole operation, the device can operate correctly which proved that it can effectively suppress DC current flowing through the main transformer netural point, to ensure the safty of transformer.The device has good engineering application results.