基于限流电抗器电压差异性的架空柔直电网故障检测方法

A Fault Protection Scheme Based on the Difference of Current-limiting Reactor Voltage for Overhead MMC Based DC grids

为检测柔直电网直流故障,需利用线路两侧的限流电抗器所提供的边界条件来设计故障保护算法。现有基于电抗器电压的保护方案存在易受过渡电阻影响、无法识别接地故障、可靠性差等问题,因此该文提出一种基于电抗器电压差异性的架空柔直电网故障保护方案。该方案利用正负极电抗器电压幅值的差异性进行故障选极;利用正负极电抗器电压之和进行故障检测。由于该方案综合了正负极电抗器电压的故障特性,因此区内外故障差异性明显,具有较强的耐过渡电阻能力;采用积分法构造判据,该方法抗噪声能力强;可靠性高,不受交流故障、断路器动作和运行方式的影响;仅使用本地测量量,故障检测时间快,满足速动性要求。最后,在PSCAD/EMTDC平台下搭建了四端MMC直流电网的电磁暂态模型,通过大量仿真,验证了所提方法在故障识别、故障选极方面的有效性,并从不同角度对多种保护方案进行了对比。

To detect DC fault for MMC based DC grids,the protection algorithms can be designed by taking advantage of the boundary effect provided by the current limiting reactors.The existing protection methods based on current-limit reactors suffer from the problems of insensitivity to fault resistance,inability to detect pole to ground faults,low reliability and so on.A protection scheme based on reactor voltage difference for overhead MMC based DC grids,was proposed.The scheme utilized the difference of the reactor voltages of the positive and negative poles for faulty pole selection;and used the sum of the reactor voltages of the positive and negative poles for fault detection.Since the proposed scheme combined the fault characteristics of the positive and negative reactor voltages,the differences between internal and external faults are obvious,making the scheme sensitive to high-resistance fault.Using the integral method to design the criterion,the method is immune to noise.In addition,the method is robust to AC faults,DCCB interruptions and operating conditions.Only local measurement is employed,so the fault detection speed is fast.Finally,the electromagnetic transient model of the four-terminal MMC DC grid was built under the PSCAD/EMTDC platform and the effectiveness of the proposed method in fault identification and faulty pole selection was verified by extensive simulations.Besides,different protection schemes were compared from different views.