直流系统大地运行时交流系统直流分布的计算

Method for the Calculation of DC Current Distribution in AC System when HVDC Operating in Ground-return Mode

为分析直流输电系统采用单极大地回路方式运行时,换流站接地极附近的中性点接地交流变压器因流入较大直流电流而导致直流偏磁等一系列不良后果,分别采用场路耦合法和电阻网络分析方法计算和比较了流入变压器中性点直流电流。结果表明,两者的计算结果相差较小,因而工程上可以采用较为简单的电阻网络分析方法计算分析直流大地电流对交流电网的影响。

When a HVDC transmission system operates in ground-return mode, large DC currents flow through the neutral earthed transformers near the converter station of the HVDC transmission system, which may lead to a series of harmful results such as DC biases of transformers. In order to analyze the problem, this paper based on specified model, the DC currents through neutral earthed transformers is calculated by using field circuit coupling method or the resistance network algorithm. The difficulty of the field-circuit coupling is how to consider the malconformation and how to analyze the influence between earth electrodes, the resistance network algorithm use the coupling resistance between the electrodes and the resistance of themselves to depict the function operating condition of the earth electrode. The results show that the calculation results are almost equal, so the resistance network algorithm can be applied to engineering for this method simplify the current-field calculation problem in field-circuit coupling method to the pure circuit problem.