Design and Implementation of Automatic Transfer Function with RTU Programmable Logics

When there is loss of incoming supply, automatic transfer is implemented in the substation to improve the System Average Interruption Duration Index (SAIDI). In current practice, only specific protection relay is used for implementing automatic transfer which is often installed for very important and critical substation with two different sources that cannot be paralleled. There are less priority for the implementation of automatic transfer in 11kV secondary substations which are less critical with multiple sources of supply. For the substation without automatic transfer being implemented, its switching operations will be executed by Authorised Person (AP) or controlled by Control Centre through sending command to Remote Terminal Unit (RTU) installed in the 11kV substation whenever there is loss of incoming supply being informed/ alerted.Currently, increasingly RTUs are installed in the 11kV substations for supervisory control and data acquisition (SCADA). However, there is no automatic transfer functionality for the non-critical 11kV substation by being not cost efficient. Hence, alternative automatic transfer solution is offered with the existing RTU installed in the 11kV substation to reduce the CAPEX. IEC 61131 Programmable Logic Control (PLC) with automatic transfer functions application is developed in RTU and tested successfully in the research laboratory environment. With this implementation, it can improve the customer satisfactory to utility as fast restoration of supply can be achieved within 10 s only.