Application of State Estimation Technique for Impedance matching to optimize Static Transfer Switch operation

The performance of complementary feeders, running in parallel, is significantly improved by installing static transfer switch (STS) at critical locations. Normally STS control logic is designed such that both feeder voltages are considered in phase and the three phase (3-Phi) line reactance of both the feeders are assumed to be equal. However, the two different feeders have different parameters and hence the phase angle between both bus voltages at the receiving end of the STS terminals is different. Depending on phase angle difference and time of disturbance, cross current phenomena occurs during switching consequently transfer time is maximized. Results show improvement in the performance of STS when weighted-least square state estimation technique has been used to estimate the phase angle at the input terminals of STS. The impedances of both feeders have been matched and phase angle difference at the STS terminals has been eliminated by installing shunt capacitor of proper size. PSCAD/EMTDC software package has been used for simulation and analysis.