Discussion on the Over-frequency Generator Tripping Scheme of the Power Grid

Abstract

The over-frequency generator-tripping and under-frequency load shedding devices play an important role as the third defensive line for frequency emergency control measures, which have a great significance for maintaining the power grid to operate safely and stably. At present, the abnormal operation frequency of hydropower generating units is mainly set based on the standard of the thermal power unit. Thus when the proportion of hydropower is too large, it can easily cause over-frequency generator tripping and under-frequency load shedding devices act one after the other, which may causes the frequency collapse. In this paper, an over-frequency cutting scheme for power grid with hydropower unit is formulated. The paper analyses and summarizes the over-frequency protection of the hydropower unit, by studying the 10 machine 39 node model with PSD-BPA software. The paper also gives a reasonable frequency action value of the high frequency cutting machine. The results show that the first-round operation value of the high-frequency cutting device of the hydropower unit should be higher than the operation value of the thermal power unit. With the first-round operation value of the high-frequency cutting device set near 52.0Hz, it can effectively avoid both of the over-frequency generator tripping and the under-frequency load shedding device, and also ensure the safety and stability of the power grid. In the hydro-thermal power grid, because of the frequency of hydropower unit cuts increasing, the power grid should remove the thermal power unit firstly, which is more beneficial for the power system frequency to stabilize rapidly.