Communication Networks for Protection Systems in Smart Transmission Grids

Abstract

The advances in Smart electric Transmission Grids (STG) have led to new developments in wide-area protection, control and state estimation applications. Protection systems in utility grids are particularly crucial in safeguarding personnel and equipment from damage. A robust, scalable and real-time Information and Communication Technology (ICT) network will be needed to support the operations in the STG.Within a substation, IEC 61850 standard provides protection and automation functions based on high-speed Ethernet Local Area Network (LAN). Guidelines have been provided to extend IEC 61850 beyond the substation to support Wide-Area Monitoring Protection and Control (WAMPAC) applications in STG. This will eventually replace the traditional IEEE c37.118 used for WAM-PAC applications, which is limited by low data rates and slow responses for fast protection applications. The ICT network plays an essential role in the delivery of timely information to the interconnected elements (i.e., substations and control center) in the STG. Therefore, the main objective set out in this thesis is to examine the role ICT networks play when protection systems are deployed in the STG. Specifically, the thesis investigates the interactions between protection applications and the ICT infrastructure, the ICT network approaches for routing IEC 61850 into wide-area, and the management of data traffic of protection applications in Ethernet networks to ensure predictable network services of delay, jitter, and packet loss. The starting point of this thesis investigates the effects of interaction between protection algorithms and the ICT architectures. The approach taken to address this is to use tools to develop a framework that can capture the effects of ICT properties such as delays, jitter, and packet losses, and hence the impact on protection algorithms can be studied. The work developed a method based on a novel co-simulation framework to assess the reliability of protection algorithms taking into account ICT impairments. The results show that by using tools with real-time properties, protection applications can be modeled and the influence of ICT parameters investigated. Additionally, the method enables to achieve hardware-in-the-loop validation by connecting real-life protection devices to the test-set up. The co-simulation platform plays a significant role in the development and validation of protection schemes before actual deployment for the future smart transmission grids. As such, it is possible to identify challenges in the early stages of protection scheme testing before actual deployment in the grid. The second topic addressed in the thesis is the support of ICT network architectures in routing IEC 61850 traffic in the STG. The work was done by evaluating ICT architectures based on the IEEE 802 family of standards. Two architectures identified and investigated were the application of Virtual LAN and IP multicast in wide-area networks. A VLAN-based communication architecture to route IEC 61850 traffic in wide-area between two substations was demonstrated, and the performance of a phasor estimation application was analyzed. Also, a method to construct network topologies from the power grid topology, meeting real-time con straints of IP multicast architectures, was proposed and analyzed. Additionally, a novel network design algorithm to meet real-time delay constraints of IP multicast networks was proposed. The network design algorithm finds additional links to be added to an existing topology such that the latency incurred on the multicast traffic are reduced. The findings show the feasibility of routing IEC 61850 protection trac with these ICT architectures. The performance of the protection trac needs to be analyzed carefully. The VLAN architecture for routing IEC 61850 trac into wide-area can be suitable but should be at best restricted to the private utility ICT networks. IP multicast provides a scalable and dynamic network architecture for routing IEC 61850 traffic. However, its performance in meeting real-time constraints is influenced by the underlying ICT infrastructure and hence should be carefully considered in the design stage. The network design algorithm will aid a faster deployment of multicast architectures as the ICT infrastructure can quickly be redesigned to meet real-time constraints. The third topic addressed is the determination of predictable network performance for tele protection traffic in Ethernet networks. Ethernet was originally designed for best-effort services. Recently, there have been efforts to define Time Sensitive Networking (TSN) services that provide methods in scheduling, trac shaping, reservation, redundancy, and synchronization to offer bounded network services. Specifically, this work investigates scheduling mechanisms of providing guaranteed QoS services (delay, jitter, and packet loss) for the tele-protection trac running in a network with other STG trac types such as management, video and file transfer. The thesis proposes a scheduling mechanism for the transport of tele-protection trac in Ethernet networks to achieve fixed low delay, minimum jitter, and zero packet loss. As such, tele-protection trac is offered a circuit-service class of hard QoS, while the other traffic in the network is offered of packet-service class with lower QoS. The results show that tele-protection trac will require TSN mechanisms to guarantee predictable QoS when deployed in ICT networks. Since the results of unpredictable QoS consequently affect the protection schemes' reliability and protection breakdown.