Studies on the Variation of Transformer Reactive Power Caused by DC Bias and Its Impacts on System Voltage

摘要

Both the Geomagnetically induced current(GIC) and the earth current of the HVDC system in unbalance operation mode can probably introduce a direct current into the transformer through the grounded neutral point, which may result in the DC bias phenomenon of transformer. Aiming at the phenomenon of the system voltage decrease under DC bias, a synchronous generator-transformer simulation model with injected direct current based on the PSCAD/EMTDC platform is established in this paper. Standing on the perspective of system reactive power balance, the transformer reactive power consumption and system voltage under steady and fault states with DC bias are simulated and analysed. The results indicate that both the steady-state and fault voltages will decrease in the case of injected direct current causing the saturation of transformer core. In addition, the system voltage decrease will accelerate with the increasing of the injected direct current. Under some extreme conditions, the decrease ratio of system voltage may exceed 9%.