Research On Optimal Configuration Of Capacitor Blocking Devices For Suppressing DC Bias In Transformers

Geomagnetic storms and HVDC transmission system can bring on transformer DC bias, which affect the safe operation of power grid. Capacitor blocking devices are usually used for suppressing DC bias of transformers. If there is no full consideration before installation, due to the complex flow routes of bias DC, the capacitor blocking device installed at neutral point of a certain transformer may lead to more severe DC bias on adjacent transformers. This paper optimizes the main parameters of the capacitor blocking device, and introduces the transformer effective bias DC as to assessment basis of transformer DC bias with considering the wiring of autotransformers and the topology of power networks. After analyzing the influence of blocking DC devices on transformer effective bias DC, this paper proposes an optimization method:under the condition of all transformers effective GIC are less than allowed limiting value, take the least quantity of DC blocking devices as optimization objective, and use genetic algorithm based on improved roulette selection method to solve the problem. As examples, the GIC equivalent model of Gan-su main power grid is built, which include 47 substations and 101 nodes; the DC equivalent model of Xizhe HVDC transmission receiving-end grid is built, which include 73 substations and 157 nodes.Based on the model, the optimal quantity and installing location of blocking devices are calculated by using genetic algorithm based on improved roulette selection method according to constraint condition and optimization objective, and the outcome is compared with that derived from the un-optimized method. The results showed that for the optimal configuration problem of capacitor blocking device,whether suppressing transformer DC bias caused by geomagnetic storms or suppressing transformer DC bias caused by HVDC transmission,optimal configuration methods are feasible and superior in this paper.