A wide-area protection system against long-term voltage collapse was designed, implemented, tested, modified, and commissioned. The system is based on the present SCADA system in southern Sweden, which has been complemented with input signals and equipment to execute action orders from the protection system. Bus voltages from the transmission system, reactive power output from generators connected to the transmission system, and current limiter information from main generators were used as input signals to the wide-area protection system. Actions from the protection system are shunt reactor disconnection, shunt capacitor connection, start of gas turbines, emergency power request from the HVDC connection to Germany, low priority load disconnection, and finally shedding of high priority load.
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