采用S变换相位差及能量相对熵的换流变零序差动保护新判据

Novel criterion adopting S-transform phase angle difference and energy relative entropy for zero-sequence differential protection of converter transformer

针对换流变压器零序差动保护误动现象,提出一种采用S变换相位差及能量相对熵算法的换流变零序差动保护新判据。通过分析换流变压器区内各类故障、区外故障及外部故障切除时零序电流的特点,利用零序差动保护两侧自产零序电流和中性线上零序电流的相位和能量概率分布差异进行识别。当发生区外故障时,零序差动保护两侧零序电流的波形极为相似,其相位差和能量相对熵值都基本为0。当发生区内故障时,零序差动保护两侧零序电流相位相反且波形相似度小,其相位差接近180°且能量相对熵值增大。仿真验证表明,该判据可准确迅速识别区内与区外故障,其性能不受故障类型和过渡电阻的影响,且具有一定的抗电流互感器饱和的能力。

In order to deal with the mal-operations of zero-sequence differential protection of converter transformer, a novel criterion adopting S-transform phase angle difference and energy relative entropy for zero-sequence differential protection of converter transformer is proposed. By analyzing the characteristics of the zero-sequence currents under different conditions of converter transformer including various internal faults, external faults and external fault removal, the differences of phase and energy probability distribution between the self-produced zero-sequence currents on both sides of zero-sequence differential protection and those on neutral line are identified. The waveforms of zero-sequence currents on two sides of zero-sequence differential protection are very similar during the external faults, both the phase difference and the energy relative entropy of which are close to zero. However, during internal faults, the zero-sequence currents on two sides of zero-sequence differential protection have opposite phases and low waveform similarity, and the phase difference is approximately 180° and the energy relative entropy is increased. The results of simulation tests indicate that immune to the fault types and transition resistances, the proposed criterion can accurately and rapidly discriminate internal and external faults with the ability of anti-saturation of current transformers.