###### Abstract  
The smart grid includes wide-area applications in which inter-substation communication is required to realize innovative monitoring, protection, and control solutions. Internet-based data exchange, i.e., communication over Internet Protocol (IP), is regarded as the latest trend for inter-substation communication. Interoperability can be achieved via the use of standardized IEC 61850-90-5 messages communicating over IP. Wide-area applications can obtain benefits from IP-multicast technologies and use a one-to-many communication model among substations communicating across a communication network. Cellular Internet is being considered as a potential cost-efficient solution which can be used for the IP-multicast communication. However, it requires knowledge of communicating uncommon IP-multicast traffic over the Internet. Moreover, it presents challenges in terms of cybersecurity and real-time requirements. These challenges must be overcome to realize authentic and correct operation of the wide-area applications. There is thus a need to examine communication security and to evaluate if the communication network characteristics satisfy the application real-time requirement. This paper investigates the secure communication of IEC61850-90-5 multicast messages over the public communication network and proposes two network architectures using the Generic Routing Encapsulation (GRE) tunnel and multipoint GRE (mGRE) within Dynamic Multipoint VPN (DMVPN). Additionally, this paper evaluates the feasibility of cellular (5G and 4G) Internet for the communication of multicast Routable Generic Object Oriented Substation Events (R-GOOSE) messages in wide-area protection applications. For this purpose, we introduce a lab setup to experiment the transmission of R-GOOSE messages within the proposed network architectures. The lab setup contains both software and hardware components. A software application is developed to publish multicast R-GOOSE with a fresh timestamp acquired from time synchronization equipment. These messages are transmitted over the Internet by computer networking devices that support cellular communication. The communication latency of the transmitted messages is measured and analyzed statistically. The statistical analysis results are discussed to evaluate performance of R-GOOSE over cellular Internet for two communication-based protection applications: Logic Selectivity and Loss-of-Main protection schemes. R-GOOSE; IEC61850-90-5 multicast over Internet; IP-multicast; inter-substation communication; smart grid +
Footnote †: journal: Accepted: 20 May 2022  
include a large number of Distributed Energy Resources (DERs). The use of DERs significantly changes the classic electricity paradigm, based on centralized power generation, and requires novel protection/control algorithms that allow for the fact that the DERs are often dispersed over a wide geographical area. Therefore, any protection/control decisions must be based on network-wide measurements and the coordinated interactions of the IEDs. The industry is responding to the challenge, and rapid developments in communication technologies and protocols have led to the design of emerging wide-area applications in the smart grid. The state-of-the-art wide-area applications provide interoperability by using standard-based messages (based on IEC61850 standards) transmitted over IP. Therefore, these wide-area applications can use IP-multicast technology. This offers not only optimized performance through better bandwidth utilization but also makes configuration simpler, since only new interested receivers need to be configured. The two IEC61850-based IP-multicast message types are Routable Sampled Value (R-SV) and R-GOOSE. These were originally defined in the IEC 61850-90-5 Technical Report [2] as standardized messages that support IP-multicast and can be used in wide-area applications. While R-SV messages simplify wide-area measurements, R-GOOSE messages enable wide-area and communication-based electrical protection.