单极接地故障下融冰装置的运行风险评估及对策研究

Ｒisk Assessment and Countermeasures for De － icing Devices under Unipolar DC Fault Condition

摘要:

对于交流侧通过换相电抗器接入变电站母线而未通过变压器隔直的直流融冰装置，当融冰线路发生单极接 地时直流正负极电压不对称，该直流电压分量通过六脉动整流阀直接耦合注入交流电网，引发中性点电压大幅度偏 移，严重时将导致 PT 饱和甚至熔丝熔断。这里评估了不同融冰方式下单极接地故障下直流融冰装置的运行风险，揭 示了 PT 饱和及熔丝熔断的机理，结合现场实际运行情况改进了现有融冰装置直流单极对地保护控制策略，并通过电 磁暂态仿真建模验证了该对策的可行性。结果表明，所提出的方法能够有效地降低直流单极接地故障下直流融冰装 置的运行风险，具有较好的实用性。

Abstract:

The de － icing devices are normally connected to the AC substation using the commutation inductance，instead of isolation transformers，which results in DC voltage coupling of the SCＲ converters to the AC networks under unipolar DC fault condition，thus causing significant neutral point voltage deviations，saturation of potential transducers ( PTs) and breakdown of fuses． The risk assessment of different de － icing methods is presented，and the mechanism of PT saturation and fuse breakdown are revealed． Based on the practical operation conditions，the protection and control strategies of the existing de － icing devices are analyzed and significantly enhanced． The effectiveness of the proposed strategy has been validated by the electromagnetic transient simulation results，and the operation risk under unipolar DC faults can be remarkably reduced，which can be widely applied in the practical applications of de － icing devices．