The role of the SCADA RTU in today's substation

The interface between Supervisory, Control and Data Acquisition (SCADA) functions and Protection and Control (P&C) functions has been blurred since the acceptance and full utilization of microprocessor based relays. The control, data acquisition and protection functions have been incorporated into a single Intelligent Electronic Device (IED). In many cases this is a clean, economically sound, solution. In some cases, the merging of the SCADA functions into a protective IED has created operation gaps that need to be addressed. There needs to be a balance of the merger so that reliability and redundancy are considered. In addition, it is important to consider how the substation can be operated if a protective relay output is not operational. The merger of SCADA with protection and control has created jurisdictional challenges since the SCADA group is a separate organization from the protection and control group. A Human Machine Interface (HMI) is being installed in substations by many utilities for monitoring and control purposes. It is important to incorporate local HMI functionality in this discussion. This paper will review several distribution and transmission substation designs that merge SCADA and Protection & Control. Each design will be discussed with advantages and disadvantages. The paper will propose designs that balance SCADA and Protection & Control and include local HMI functionality, IED access and security.