单相接地时LCC-HVDC换相失败时序机理研究

Time Series Mechanism of LCC-HVDC Commutation Failure in Single Phase Grounding

为准确掌握换流站交流母线发生单相接地故障时,高压直流输电系统中容易发生换相失败的换流阀,以便从原理上采取针对性更强的换相失败抑制措施,以A相故障为例推导出换流站母线电压以及换流变换相电压幅值和相角变化量故障前后随接地电阻、接地电抗之间的数学关系式,影响故障后首次换相时换相失败顺序的因素包括故障相别、系统等值阻抗、接地阻抗和换流变接线组别。进一步通过计算故障前后换流阀的换相面积比值,找出故障发生后更容易发生换相失败的换流阀。换流站母线通过电抗接地时,接地故障发生后首次换相的阀容易发生换相失败的顺序相同,A相故障时依次为Y3(Y6)、D5(D2)、D3(D6),其余阀在故障发生后首次换相时不会发生换相失败。但通过电阻接地时,容易发生换相失败的换流阀顺序与接地电阻大小密切相关,详细推导出不同接地电阻范围内故障后首次换相时容易发生换相失败的换流阀顺序,并在PSCAD/EMTDC电磁暂态仿真软件中的CIGRE高压直流标准测试系统及实际工程模型中验证了文中理论研究结果的正确性。

When a single-phase grounding failure of the AC bus in the converter station occurs,the converter valves in the high voltage direct current(HVDC)transmission system are prone to commutation failures.It is urgent to take more specific measures to suppress the commutation failures in theory.Taking an A-phase fault as an example,the mathematical relationship is deduced between the bus voltage of the converter station,the converter phase voltage amplitude and the phase angle variation with grounding resistance and grounding reactance before and after the fault.The factors affecting the sequence of commutation failures during the first commutation after the A-phase fault include the fault phase difference,the system equivalent impedance,the grounding impedance and the connection group of the converter transformer.Further,by calculating the ratio of the commutation area of the converter valve before and after the fault,the commutation valve which is more likely to fail after the fault occurs is found out.When the bus of the converter station is grounded by reactance,the first commutation failure of the valves after the grounding failure occurs in the same order.When the phase A failure occurs,the first commutation failure of the valves is Y3(Y6)、D5(D2)、D3(D6),and other valves may not commutation fail during the first commutation after the fault occurs.However,when grounded by resistance,the sequence of the commutation valves which are prone to commutation failures is closely related to the size of the grounding resistance.The sequence of the commutation valves which are prone to the commutation failure during the first commutation after failures within different grounding resistance ranges is deduced in detail.The correctness of the theoretical research results is verified in the CIGRE HVDC standard test system and the actual engineering model in the PSCAD/EMTDC electromagnetic transient simulation software.