A Two-stage Emergency Control Method for Local Power Grids in Mega Cities Considering off Grid Survival

Local power grids of 220kV and below in mega cities may switch to an off grid state using traditional emergency control methods of cutting off machines and loads after extreme faults or instability occur in the superior power grid. This may result in transient low voltage, high frequency, high voltage, and low frequency situations, causing power grid instability and loss of power supply to important loads. Firstly, this article elaborates on the characteristics of mega urban power grids from the source network load side; Analyzed the reasons for voltage and frequency coupling in local power grids and the shortcomings of traditional emergency measures to address this phenomenon; Secondly, in response to the control requirements of avoiding transient low voltage high frequency and steady-state flat voltage high frequency after leaving the grid, a two-stage emergency control method for electrical quantity response is proposed. This method incorporates capacitor banks into the emergency control system and cooperates with load shedding and other operations in a timely manner to solve the contradiction between transient low voltage high frequency and steady-state flat voltage high frequency caused by rapid recovery of transient voltage. Finally, the feasibility and effectiveness of the emergency control method proposed in this paper were verified based on a 220kV local power grid in a certain region of China.