混压同塔四回线跨电压不接地故障下的距离保护适应性分析

混压同塔多回线输电方式因其具有传输容量大、占用土地资源少等优势,在国内外得以较多应用。两个不同电压等级线路间的跨电压故障是混压同塔输电方式下的一种常见故障形式,已有文献开展了跨电压接地故障对距离保护的影响研究。但对于跨电压不接地故障,因其分析更为复杂,尚未见相关研究。以跨电压不接地故障为研究对象,分析了其对接地距离保护和相间距离保护的影响。基于复合序网的混压同塔多回线跨电压故障分析方法,计算分析了跨电压不接地故障时测量阻抗的变化规律,得出其大小与故障点位置和两不同电压系统特殊相电源相角差有关的结论,并进一步指出其与接地故障下的测量阻抗区别及其原因。同时对非完全故障相的相间距离保护的动作情况进行了讨论,指出其存在误动的可能性。最后,在PSCAD中构建了500 kV/220 kV混压同塔四回输电线路模型,通过大量仿真实验,验证了理论分析的正确性。

Analysis of the adaption of distance relay in the case of cross-voltage phase to phase fault occurring on mixed-voltage quadruple-circuit transmission lines on the same tower

The mixed-voltage multi-circuit transmission lines are widely used at home and abroad because of its advantages of large transmission capacity and small land resources. The cross-voltage fault between two different voltage-level lines is a common fault form under the mixed-line transmission mode. The literature has studied the influence of the grounding condition of the fault on the distance protection. No literature about non-grounding cross-voltage short-circuit is found, and it is more difficult to analyze. In this paper, the cross-voltage phase-to-phase fault is taken as the object, and its influence on ground and phase-to-phase distance protection is analyzed separately. Based on the method of calculating the fault current of mixed-voltage lines on the same tower in the composite sequence network, this paper calculates the variation law of the measured impedance when the non-grounding cross-voltage short-circuit occurs, draws the conclusion that the amount is related to the position of the fault point and the phase angle of the special phase of the two systems, and points out the difference between them and its cause. The performance of the phase-to-phase distance protection of the non-complete fault phase is discussed, and the possibility of maloperation is pointed out. Finally, a model of 500 kV/220 kV four-circuit transmission line on the same tower is built in PSCAD to verify the proposed analysis. This work is supported by National Key Research and Development Program of China:Key Projects of Smart Grid Technology and Equipment (No. 2016YFB0900600).