Implementing Distributed Intelligence by Utilizing DNP3 Protocol for Distribution Automation Application

The growing adoption of Distributed Energy Resources (DERs) such as rooftop solar, onsite energy storage and electric vehicles requires power utilities to support increasing grid interconnections, and higher system reliability standards. This electrical distribution grid of the near future requires advanced distribution automation applications to provide foundational grid capabilities. These capabilities include advance Fault Detection Isolation and Restoration (FLISR) functionality. For correct and reliable grid operation, these advance distribution automation applications should consider various load restoration scenarios and significant amount of dynamically changing distributed energy recourses. These factors increase the complexity of the algorithms used by the applications and require reliable communication systems to exchange all critical information between the automation controllers in the field. To support the future distribution grid, authors believe for fast, reliable, and efficient operations such automation systems should have intelligence at the edge of the network. To achieve this goal, authors are developing a modern distribution automation control system with advanced protection and automation logic capabilities utilizing distributed intelligence architecture. As an added benefit of the distributed intelligence approach, this new automation system has a minimal impact on SCE's existing distribution, substation protection, and grid management systems. Resulting in a drop into place solution, which is interoperable with existing systems. The chosen communication system, however, ultimately defines the reliability of the entire system and its operating speed. For approximately 25 years, Southern California Edison has utilized a mesh connected radio system, called Netcom, for supervisory control and data acquisition (SCADA), which now contains over fifty thousand nodes. This system works with sub-gigahertz frequency, thus having very good propagation and reliability. However, the radio terminals operate with serial interface utilizing the DNP3 protocol that does not support a large-scale peer-to-peer data exchange. The distributed intelligence application logic can efficiently work if multiple devices can quickly exchange fault information to make operational decisions. To achieve this, status and critical fault information from any field controller must be available to the rest of the system. In order to leverage SCE's Netcom system and perform peer-to-peer data exchange over the DNP protocol, authors developed the new DNP Router concept. The DNP Router allows a DNP based communication system to mimic a publisher-subscriber communications model by polling individual controllers in the field and sending (a.k.a. publishing) the acquired information back to assigned (a.k.a. subscribed) system components via commands. However, the legacy Netcom communication system has a number of limitations which includes packet size and bandwidth capacity. These factors minimized the ability to use unsolicited response from the field devices. Unlike conventional RTUs, the DNP router should have capability to dynamically determine which devices to poll and in what sequence. Article will illustrate development phases from proof of concept to testing and successful commissioning of the first system. Authors will discuss the algorithms implemented on the DNP Router to dynamically optimize the data exchange during fault events. These measures increased the operating speed of the system, demonstrating the majority of automatic FLISR operations can occur within two minutes. Authors will show how legacy communication systems can be employed by modern distribution automation systems with advanced protection and automation logic capabilities.