Use of local measurements to estimate voltage-stability margin

Estimating the proximity of power systems to voltage collapse in real time still faces difficulties. Beside the data management and computational issues, any central control method is subject to the reliability of long-distance data communications. In the paper, the authors describe a new data processing method to estimate the proximity to voltage collapse. The method (code-named SMARTDevice, for Stability Monitoring And Reference Tuning Device) employs only local measurements-bus voltage and load current-and calculates the strength of the transmission system relative to the bus. The collapse occurs when the local load approaches this value. The method is simple enough so that it can be implemented in a numerical relay. The performance of SMARTDevice is compared against the conventional undervoltage relay. It is shown that the latter can misoperate while the new device does not. SMARTDevice is in fact a new breed of voltage relays whose setpoint is automatically tuned to the system condition.