Control and Protection Cooperation Strategy for Voltage Instability

Most cascaded blackouts are caused by unexpected backup relay operations due to low voltage or overload state caused by post fault load restoration dynamics. If such state can be sensed and adjusted appropriately prior to those relay actions, system stability might be sustained. This paper proposed a control and protection cooperation strategy to prevent post fault voltage instability. The multi-agent technology is applied for the strategy implementation; the criteria based on wide area measured apparent impedances are defined to choose the control strategy, such as tap changer adjusting or load shedding; and the sensitivity based load shedding has been adopted to save the system from severe states. A test system is built in real time digital simulator (RTDS) and has demonstrated the effectiveness of the proposed method.