Online Security Early Warning And Decision Support System (EWDSS) For Urban Power Network

During the past years, blackouts in the power system occurred over the world. The shortcomings of EMS were exposed to the dispatching centre, and an intelligent security early warning system is required. The security early warning system should observe the real-time state of power system, carry out the analysis of power system security assessment, find the hidden fault and send the security early warning report to the dispatcher, who will decide the measure of fault disposal to keep the security of power grid.In this paper, the structure of on-line security early warning and decision support system (EWDSS) for urban power grid are presented. In the urban power grid, the problem of angle stability can be ignored, but the thermal stability problem is obvious. So, the on-line security early warning and decision support system is discussed from several professional aspects.Urban power grids generally used loop power network designed, radial running mode. When there were faults or maintenance in urban power grid, the power loads were transferred through closing loop operation to avoid blackouts of consumers and improve the reliability of power supply. As the performance of the grid after closing loop was opaque to the dispatcher and to judge the feasibility of closing loop was difficult, the loop power flow was sometimes too large, which would cause lines or equipments overload, relay action and blackouts of consumers. After China's 220 kV power grid division, closing loop operation between different regions of central power supply has puzzled the actual operation of the electricity production, and the phenomenon of relay action due to large loop power flow repeatedly appeared in many cities. So, an on-line loop power flow calculation method is required to calculate the loop power flow in advance, and the dispatcher could be instructed to hold the best time of closing loop to ensure the safety of equipments and improve the reliability of power supply.Closing loop operation and calculation of loop power flow are studied in this paper. Based on the study, the function of on-line loop power flow calculation (state estimation on active power) of the EWDSS are designed and realized. State estimation on active power is established on the characteristics that in urban power grid the active power is closely relate to phase-angle and feebly relate to the voltage amplitude, and the precision of active power measurement was high. So, only the active power and phase measured value are taken into account in the state estimation. So this arithmetic can improve the speed and precision of state estimation, and minimize the dependence on the basic data. Loop power flow calculation function is realized on State estimation on active power. It can fast calculate the loop power flow and supply the analyzed result of loop power flow and the early warning and decision support information to the dispatcher, who can choose the best closing loop point or the best time to close the switch.