## 1 Introduction  
Smart grid communication protocols have a wide range of applications to serve the growing complexity of modern electrical grids. As Distributed Energy Resources (DERs) become more commonplace, grid complexity and the associated network complexity for monitoring and control increase in order to meet the increase in demand and ensure the safe operation of grid resources. Some commonly used non-proprietary protocols for Supervisory Control and Data Acquisition (SCADA) and substation communication in North America are DNP3, Modbus, and IEC-61850 [1]. The IEC-61850 protocol suite is designed for greater visibility into smart grid devices at the process, bay, and station levels. At its core, it consists of the Generic Object-Oriented Substation Event (GOOSE), Sampled Value (SV), and Manufacturing Message Specification (MMS) protocols [2]. Among these protocols, GOOSE is capable of both substation and SCADA communications. It utilizes an 802.1Q multi-casting feature that transmits unencrypted data at the station level, whereas Routable GOOSE (R-GOOSE) encapsulates GOOSE packets for delivery to SCADA systems. Modbus and DNP3 are often used for reporting and have higher latency tolerances. They utilize session-based TCP communications and support TLS for security [3; 4]. The use of wireless networks for smart grid operations can ease the support of communications for DERs or different grid components over large geographical distances and make networks easier to re-configure without changing the grid infrastructure or the cost associated with installing large wired networks. As one prominent example of wireless technologies of interest for such wireless transitions, 5G also contains policy enforcement capabilities for security, which can be leveraged to transition toward a secure zero-trust architecture [5]. The capabilities of 5G can, in part, be attributed to advancements in antenna design, providing higher gain with smaller footprints [6]. These advancements allow for a higher density of connected devices on wireless networks compared to previous cellular generations [7]. The added security of 5G can also mitigate vulnerabilities for protocols such as GOOSE [8], which multi-cast plain text messages over their networks. Full implementation of the recommended security features of 5G would also mitigate vulnerabilities found in the Modbus and DNP3 protocols, which have been shown to be susceptible to Man-in-the-Middle (MiTM) attacks and False Data Injection Attacks (FDIAs) [9; 10]. In this paper, we evaluate the latency impact of incorporating 5G communication for OT protocols (both with and without low-latency requirements) commonly used in substation communications. Specifically, we examine the latency impact on the communications of IEC-61850 GOOSE, Modbus, and DNP3, considering the latency both in a standard deployment and when communicating over 5G. For the testbed in our study, we utilize the implementation provided by the OpenAirInterface (OAI) open-source project [11; 12], which allows us to establish a full 5G core and Radio Access Network (RAN) to represent, for example, a private 5G network for substation communications. We also perform in-depth latency measurements for each component of the 5G testbed, isolating the factors critical to our measured latency. We utilize these obtained results to investigate the feasibility of transitioning these protocols directly to 5G operations. Our research results presented in this paper show that the latency introduced through simple encapsulation of OT protocols using 5G as the transport mechanism is suitable for non-critical smart grid protocols but not for time-sensitive protocols like IEC-61850 GOOSE. Our study shows that a further reduction in latency is required to accommodate time-critical smart grid applications. The remainder of the paper is structured as follows.