变压器后备保护拒动原因分析与改进

Analysis and Improvement on Mal-Operation of Transformer Backup Protection

结合起变压器相间短路后备保护拒动事故,实例计算分析了变压器负荷侧复压过流保护中低电压元件、负序电压元件和过电流元件对变压器相邻线路的保护范围,指出当相邻线路远端发生故障时,如果故障线路自身的保护装置或断路器拒动,而该侧主变后备保护灵敏度不足,将无法可靠切除故障,导致事故范围扩大。针对该问题,提出了种基于补偿电压正序分量的变压器相间短路后备保护方法,该方法通过在线计算补偿电压正序分量的幅值及其极性来判断故障点位置,根据线路长度整定保护动作值,自动调节保护范围。分析表明,该方法不受系统运行方式、线路长度与故障点位置的影响,且几乎不受过渡电阻的影响。在变压器负荷侧装设该保护来替代传统复压过流保护,能够保护变压器相邻母线和线路全长,有效解决了配电网中复压过流保护对本侧出线灵敏度不足的问题。

Based on a case of mal-operation of backup protection for transformer phase-to-phase faults, this study calculates and analyzes the protection range of low-voltage component, negative-voltage component and overcurrent component. It is pointed out that the sensitivity of overcurrent protection with composite start-up voltage is not enough to reliably clear the fault when a short circuit fault occurs at the remote terminal of a close-in line. To tackle the problem, a method of transformer backup protection based on positive component of compensating voltage is presented. Fault point location is judged with the amplitude and polarity of positive component of compensating voltage, obtained by real-time calculation, and protection scope is automatically adjusted depending on the line length. Installing protection of this kind on the load side of transformers to replace the traditional overcurrent protection with composite start-up voltage can protect the adjacent bus and the whole line. Analysis shows the method is correct and reliable without effect from operational mode of power system, line length, fault point location and transient resistance.