Experience on the serial interfacing of protection relays to telecontrol systems

Digital substation architecture, offers the user significant savings in cabling costs and commissioning time. Substation RTUs (remote terminal units) become smaller and more cost effective as the traditional input/output cards are no longer required. From the operational point of view, the user has access to large amounts of data gathered by the protection relay. This can be used to optimise the operation of the electrical network as well as reducing the plant maintenance effort. However, only a few Regional Electricity Companies (RECs) have reaped the benefits of the digital architecture. The two main obstacles have been: the lack of RTUs capable of communicating with protection relays (most installed RTUs are part of the first generation SCADA systems and have no facilities for serial interfacing to slave devices); and the existing organisation of the RECs is not ideally suited to deal with integrated protection and control (separate teams dealing with protection and telecontrol activities, without a clear line of responsibility for the complete system). This paper describes the experience of a SCADA systems supplier that has successfully developed serial interfaces to protection relays from several vendors. Results of tests carried out to evaluate the performance of the serial interface between the company´s own protection relays and RTU are presented. The future of the substation RTU, as well as the impact of evolving international standards are discussed