Setting strategy of instantaneous current quick-breaking protection for mine power grid

The mine power grid operating environment is poor. When a short circuit fault occurs in the underground power supply system, the use of complex anti-skip trip protection device will reduce the reliability of the entire power grid and increase the cost. The mine power grid needs to ensure that the current quick-break protection can act instantaneously to remove the short circuit fault, especially at the line outlet. The current mine power grid protection scheme of the anti-skip trip can not take into account the protection quick-action, power supply reliability and equipment economy. In order to solve the above problems, according to the minimum principle that short-circuit accident in the mine power grid can not skip to the ground, a setting strategy of instantaneous current quick-breaking protection for mine power grid based on the overall optimal principle is proposed. The relationship between the short-circuit current value and the location of short-circuit point and the distribution characteristics of short-circuit current at the beginning and end of the line are analyzed. The shortcomings of the traditional single-setting method are compared and studied. Three indexes are defined, which are minimum-maximum system impedance ratio, maximum system impedance and line impedance ratio, and adjacent line impedance ratio. The indexes are used to represent characteristic relational expressions of different short-circuit current distribution scenarios and conditions for each setting method to meet the requirements. The setting methods applicable to instantaneous current quick-breaking protection under different short-circuit current distribution scenarios are determined. The corresponding optimal setting strategy flow is proposed. Taking a typical mine power supply line as an example, according to the proposed setting strategy, the setting calculation of the protection switch at all levels is carried out. The results show that the setting strategy is used to set five protection switches with the risk of the skip trip in the mine power grid model. The protection range of four protection switches can be controlled within the two-level line. The times of skip trip accidents are reduced. The probability of underground short-circuit faults extending to the surface of the mine power grid is reduced.