交直流互联系统对换流变压器差动保护的影响分析及对策

换相失败会对变压器的保护性能产生影响。首先,基于叠加开关函数法分析了换相失败导致变压器饱和的机理。然后,重点研究了变压器差动保护在换相失败期间的动作性能。研究结果表明,变压器发生外部故障时差动保护一般不会误动,但变压器发生内部故障时则可能拒动。现有的基于二次谐波制动方案的差动保护并不能较好地适应交直流互联系统。为此,提出了带有新逻辑的综合制动方案。该方案能够保证换流变压器在内部故障时差动保护可靠动作,同时在外部故障时将差动保护可靠闭锁。最后,由PSCAD/EMTDC仿真结果验证了所提方案的正确性和有效性。

Effect of AC/DC Interconnected Network on Transformer Protection and Its Countermeasures

Adverse impact on transformer protection performance will occur when commutation failure happens. First, the mechanism of transformer saturation caused by commutation failure is researched based on the addition switching function. Then, the effect of commutation failure on the transformer differential protection is studied in detail. The analysis result shows that the differential protection is seldom affected by commutation failure while there is only an external fault in the transformer,but it may cause trip failure during an internal fault. The existing traditional differential protection with second harmonic restraint cannot well adapt to the AC/DC interconnected network. In order to solve this problem, a synthetic restraining scheme with a new logic is proposed, which is capable of ensuring the reliability of differential protection during an internal fault, while the differential protection is blocked during an external fault by a novel restraining scheme. The correctness and effectiveness of the proposed scheme is verified by simulation results. This work is supported by National Basic Research Program of China (973 Program) (No. 2012CB215206) and the Fundamental Research Funds for the Central Universities (No. 2015XS16).