Improving base case solution for on-line ATC calculations

The base case for computing available transfer capability (ATC) may be from the real-time state estimation (SE) or a future postulated system condition. Many existing ATC calculations are using off-line planning models. A survey result shows that most transaction business will take place in the next hour. In a network with limited transmission margins, to accommodate the next-hour market, there exists a need for an accurate real-time network model that can be used in the on-line ATC calculations. Due to the data exchange activity in the interconnected network, measurements used in an on-line model estimation might occur, say, as much as 30 seconds or several minutes apart. This paper investigates the measurement time skew effects in the real-time ATC calculations. In order to reduce the time skew effect, three measurement treatment schemes including a linear extrapolation scheme, an exponential smoothing scheme and a dynamic state estimation (DSE) are proposed. Test results show that with proper measurement updates, SE can provide a more accurate real-time base case for security analysis and ATC calculations. Costly overdesign of communication system for interarea data exchange could be avoided by using the proposed methods