STATE ESTIMATON TECHNIQUE FOR IMPEDANCE MATCHING IN DISTRIBUTION FEEDER RECONFIGURATION

Abstract

State estimation has been adopted by the power system researchers in the late 1960’s. Later on, state estimation was applied to the transmission system. Recently state estimation has become cornerstone among the modern control centers tools for the automation of distribution system. In this research work, state estimation has been implemented for automatic feeder reconfiguration. Automatic feeder reconfiguration can be accomplished by matching the impedances of two different feeders. Once the impedances are matched, static transfer switch perform the feeder reconfiguration effectively and efficiently. The liability of power distribution companies is to provide reliable and good quality power to the customers. Due to the technological advancement and the large scale production, usage of the sensitive equipment has been increased. The sensitive equipment requires quality power through reliable power delivery system. Power delivery system includes feeders and laterals to transfer power from the substation to the consumer end. As the feeders and the laterals are radially operated, therefore the chances of power interruption always exist. Power interruption may occur either due to faults or due to the maintenance or replacement of any components of the distribution system e.g. a distribution transformer. Voltage sag is another cause of interruption of sensitive equipment. To overcome this problem, sensitive equipment should be fed through two independent feeders. If the preferred feeder fails, the sensitive load should be transferred to the alternate feeder. A fast and efficient transfer switch can complete this transfer. Static transfer switch (STS) system has been developed to transfer the load from the preferred feeder to the alternate feeder when voltage sag or fault occurs on the preferred feeder. The most important parameter of the STS-system is the speed of operation or the transfer time so that the load should not be interrupted. To reduce the transfer time and hence to expedite the transfer process, it is necessary that both feeders have the same voltage angle at the point-of-installation (PoI) of the STS. If the impedances of both the feeders are identical then voltage phase difference will be zero. To match the impedance, state estimator has been designed to estimate the voltage angle of both the feeders. To mitigate the voltage phase difference, shunt capacitor has been installed and consequently the transfer time of the STS has been reduced. However, the control logic strategy of the STS-system also affect the transfer time. Two different control logic techniques namely delay logic and forced commutation technique, have been developed and simulated using PSCAD/EMTDC software. If the delay logic technique is utilized then the voltage phase angle of both feeders must be identical. The developed state estimation technique can be implemented to match the impedances and hence the voltage angle to reduce the STS transfer time. However, forced commutation technique can accommodate the phase difference by commutating the outgoing thyristor forcefully. But forced commutation technique require more components e.g. capacitor, inductor, auxiliary thyristors etc. Both techniques are implemented to solve the problems related to the feeder overloading. The problem of overloading has been solved through feeder reconfiguration. STS-system installed at critical location, transfer the sensitive load to the lightly loaded alternate feeder. This phenomenon can be termed as feeder reconfiguration using load-balancing. The development of the STS-system has solved the problem of load interruption. The reliability of the power distribution system has been improved and the sensitive load now operates without power interruption.