特高压有载调压变压器差动保护自适应算法

有载调压技术已在中国特高压交流输电系统中实现了应用,这对特高压变压器运行的可靠性提出了更高要求。有载调压过程中,由于无法获知调压变压器的实际运行档位,差动保护装置不能根据实时的额定电流之比调整平衡系数,只能选取一个固定档位下调压变压器两侧额定电流之比来计算其差动电流,因而会造成很大误差。工程上,设置调压变压器不灵敏段差动来躲过调档产生的不平衡电流,这不仅增加了调压操作的复杂性,还降低了调压变压器差动保护的灵敏度。针对上述问题,基于特高压变压器电气结构提出一种在线自适应获取调压变压器运行档位的方法,通过实时计算调压变压器运行时的端电压之比,对差动电流计算结果进行修正,精确求得有载调压过程中调压变压器的实时差动电流。数字仿真证明了基于自适应算法的调压变压器差动保护动作特性不受短路匝数和运行档位变化影响,可有效解决现有特高压有载调压变压器差动保护策略识别匝间故障时灵敏度不足的问题。

An Adaptive Algorithm for the Differential Protection of the UHV Voltage-Regulating Transformer with On-Load Tap Changer

On-load voltage regulation technology has been successfully applied in the ultra-high voltage (UHV) transmission system, leading to a higher requirement for operating reliability of the UHV transformer. During on-load voltage regulating process, it is impossible to adjust the balance coefficient since the actual tap position of the voltage-regulating transformer (VRT) is unavailable for the protection relay. Thus, a fixed ratio is chosen to calculate the differential current, which may probably exist great errors. In practical engineering, the insensitive differential protection is added to avoid the unbalanced current caused by voltage regulation, which increases the complexity of the field operation and decreases the sensitivity of the relay action. Thus, this paper proposes a new method to identify the online tap position adaptively based on the structure of the UHV transformer. The differential current is modified by calculating the online ratio of the VRT to obtain the accurate value during online voltage-regulating process. Digital simulations have demonstrated that the percentage of short-circuit turns and the online tap position have little effect on the operating characteristic of the adaptive differential protection. The sensitivity deficiency of the existing protection strategy is effectively solved during the turn-to-turn faults.