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# Smart5Grid Testing Strategy & Field Implementations for RT Wide Area Monitoring of Interconnected Systems

Ioannis P. Chochliouros<fnref n="1" />(✉), Dimitrios Brodimas<fnref n="2" />, Nikolaos Tzanis<fnref n="2" />, Michalis Rantopoulos<fnref n="1" />, Daniel Shangov<fnref n="3" />, Georgi Hristov<fnref n="4" />, Atanas Velkov<fnref n="4" />, Irina Ciornei⁵, and Daniele Porcu<fnref n="6" />

**Abstract.** The integration of renewable energy sources in the electrical grid imposes several operational issues for the energy markets and the transmission system operators, in particular. It is of great importance not only to detect events, but also to react in time to prevent faults in the transmission system that could lead to outages for the consumers or even to permanent damage to the energy equipment. Towards this scope, the criticality of the role of the Phasor Measurement Units (PMUs) which provide readings of voltage, frequency and current, is explained in this paper. It is also discussed how the 5G network may assist in the transfer of the measurements with its low latency capabilities and high availability criteria. Based on a Smart5Grid project's dedicated use case, the concept of 5G enhanced wide area monitoring is presented along with the associated field platform implementations both in Greece and Bulgaria. A complete list of defined Field Platform Validation Metrics is also elaborated with the equivalent targeted values.

**Keywords:** 5G · energy vertical ecosystem · latency · Network Applications · network slicing · smart-grid · wide area monitoring (WAM) · network functions virtualization (NFV) · synchrophasor · Phasor Measurement Unit (PMU)

## 1 Introduction

Current electrical grids consist of large and interconnected power systems which have served well modern societies in providing the necessary power supply of electricity. However, factors such as the growing demand, fast depletion of energy sources, unreliability and impact on the environment must be responded to in a vision of the future. The

<footnote n="1">¹ Hellenic Telecommunications Organization (OTE) S.A., 99 Kifissias Avenue, 15124 Maroussi-Athens, Greece
ichochliouros@oteresearch.gr</footnote>

<footnote n="2">² Independent Power Transmission Operator S.A., Athens, Greece</footnote>

<footnote n="3">³ Bulgarian Electricity System Operator ESO EAD, Sofia, Bulgaria</footnote>

<footnote n="4">⁴ Vivacom (Bulgarska Telekomunikatsionna Kompaniya EAD), Sofia, Bulgaria
⁵ University of Cyprus, Nicosia, Cyprus</footnote>

<footnote n="6">⁶ Enel Global Infrastructure and Networks Srl, Rome, Italy</footnote>
smart grid is a new paradigm shift that combines the electricity, information, and communication infrastructures to create a more reliable, stable, accessible, flexible, clean, and efficient electric energy system. The smart grid can be considered as a modern electric power grid infrastructure for enhanced efficiency and reliability through automated control, high-power converters, modern communications infrastructure, sensing and metering technologies, and modern energy management techniques based on the optimization of on-demand, energy and network availability. A smart grid uses digital technology to improve reliability, security, and efficiency of the electric system from large generation, through the delivery systems to electricity consumers and a growing number of distributed-generation and storage resources [1]. Thus, a smart grid brings the power of networked, interactive technologies into an electricity system, giving both utilities and consumers exceptional control over energy use, improving power grid operations and, ultimately, reducing costs to consumers. So far, the communication networks dedicated for the needs of power control and automation were handled by the Transmission Systems Operators (TSOs), whereas telecom operators played almost no role in the power grids communication infrastructure. This is expected to change in the era of smart grid [2, 3] with the latter being the basis of smart energy and assessed as an important factor for promoting economic and social coordination as well as sustainable development. It can also provide strong support for a better life, cleaner environment and a more harmonious society.

Fifth Generation (5G) Networks will be an important enabler for the development of smart grid technologies [4]. The smart grid business, as one of the senior representatives of the vertical industry, has brought a lot of challenges to the communication network with its rich and diverse business types and differentiated industry needs. The advantages of 5G over earlier generations include higher data rate and low communication latency, improved security and reliability, low power consumption, and ability to connect a higher number of devices. As a consequence, 5G networks can very efficiently deal with several among the smart grid-related challenges faced by utility companies, such as connecting a vast number of sensors and providing ubiquitous coverage with high security and reliability [5, 6]. Furthermore, the 5G networks are able not only to propose but also to establish and make operational a new service-based architecture with advanced wireless technologies to deliver innovative business use-cases requiring low latency, increased capacity, high reliability and flexibility to satisfy the needs of different services [7, 8]. In this respect, the adaptation of 5G in the energy vertical will allow the grid to integrate to the dynamics of renewable energy and distributed generation [9, 10].

Solar and wind power tend to become prevalent in the near future [11], demanding more efficient monitoring and control mechanisms. Towards this direction, 5G networks will assist smart grids to control easier bi-directional power flows and support distributed energy resources. The 5G Networks capabilities providing low latency, large bandwidth, ultra high reliability and massive connection “match” the service requirements of the smart grids [12]. As one of the unconventional 5G technologies, the network slicing technology can divide the physical network into several independent, isolated and demand-based logical networks, which can ensure the efficient customization and smooth-going of various service needs. In this scope, 5G network technology can process and integrate network resources according to different user needs and scene characteristics and
provide users with exclusively customized services. Three key sets of Network Slices [13, 14] in 3GPP have been defined for 5G Networks: massive Machine Type Communications (mMTC) for efficient monitoring of remote equipment, ultra-Reliable and Low Latency Communication (uRLLC) for handling of time-bounded traffic data and enhanced Mobile Broadband (eMBB) for handling of higher amounts of data in densely populated areas. These features along with the flexibility of the 5G Networks technology could enable a significant shift for the smart grid's communication layer.

The present paper is composed by several distinct sections: Sect. 1 identifies the strong innovative correlation between the 5G capabilities and smart grid's service requirements. Section 2 provides an overview of the concept of Smart5Grid and highlights its functional architecture with its 3 distinct layers. Section 3 discusses the respective use case 4 (UC#4), focusing on its conceptual descriptions, its proposed services related to UC-specific Network Applications and the inclusion of 5G technology. It also gives a high level view of the field implementations for the Greek and Bulgarian sides and illustrates the main network components. Section 4 depicts UC#4's Testing Strategy by reviewing the Field Platform Validation Metrics (FPVMs) developed for its needs. Section 5 serves as an overview.

## 2 The Smart5G Concept and Functional Architecture

The Smart5Grid EU-funded project [15] faces all the above challenges by providing an innovative, open and 5G enabled experimentation platform for the benefit of the energy market vertical [16]. Synoptically, Smart5Grid's aim is to assist the integration of modern energy grids to 5G network resources. This will be achieved through the open experimentation platform and the associated newly created Network Applications [17].

A Network Application is a piece of software that interacts with the control plane of a mobile network by consuming the exposed Application Programmable Interfaces (APIs), e.g., northbound APIs of 5G core and RAN Intelligent Controller (RIC), and edge computing APIs, in a standardized and trusted manner to compose services for the vertical industries. Network Applications can provide services to vertical applications, either as an integrated part within the vertical application or by exposing APIs (called business APIs). The Network Applications allow developers to concentrate on building the applications that are specific to the vertical domain on which they concentrate their expertise, while leveraging the features and performance that 5G networks offer. Network Applications enable them to do so by creating an abstraction of the complexities of the 5G network into a set of requirements, captured formally in a Network Application descriptor. The corresponding ecosystem is more than the introduction of new vertical applications that have interaction capabilities. It refers to the need for a separate middleware layer to simplify the implementation and deployment of vertical systems on a large scale.

Smart5Grid constitutes a step forward in the integration of energy grids with the latest innovations in virtualization and communication technologies that 5G, brings [18, 19]. Thus, Smart5Grid may be regarded as an ecosystem where professionals from various fields such as Telco experts, Software Developers, ICT integrators, Institute Researchers and Energy operators, work interactively towards the goal of utilizing the opportunities
offered by the 5G Networks. Smart5Grid is one of the 19 European selected projects to deal with “5G innovations for verticals with third party services & Smart Connectivity beyond 5G” [20]. In concrete, the project responds to the dedicated 5G-PPP ICT-41-2020 Call [21]. The main common objective of the nine selected projects funded under this Call is to provide 5G open experimental platforms that attract and provide opportunities for SMEs and developers to test Network Applications for specific vertical sectors and to create open-source repositories of such applications for wide use and towards standards development.

Four real-life scenarios will be demonstrated targeting to the Renewable Energy Sources (RES) production and distribution [22]. UC#1 in Italy deals with fault-detection and self-healing of the power distribution grids. UC#2 in Spain considers the critical issue of workers’ safety in High-Voltage (HV) power substations. UC#3 in Bulgaria demonstrates a millisecond level precise distributed generation monitoring for a wind, hydro and photovoltaic power plant. UC#4 monitors in real-time the wide-area transmission grids between the borders of Greece and Bulgaria.

Smart5Grid leverages on network slicing (NS) [23–25] which refers to partitioning of one physical network into multiple virtual networks, each architected and optimized for a specific application/service. Specifically speaking, a network slice is a virtual network that is created on top of a physical network in such a way that it gives the illusion to the slice tenant of operating its own dedicated physical network with its own Service Level Agreements (SLAs) [26]. This is particularly beneficial for the Network Requirements fulfilment of the newly developed Network Applications thus enhancing the features of the proposed smart grids. Additionally, NS due to its ability to support differentiated service scenarios, can be viewed as the main enabler that will help smart grid actors to significantly reduce the Total Cost of Ownership (TCO) at power communication networks.

The Smart5Grid platform [27] aims to provide a common place for application developers and consumers within the vertical market of energy grid applications. In order to achieve this goal, Smart5Grid will develop a list of thoroughly tested Network Applications hosted in the Open Service Repository (OSR), made available for consumers to use. Figure 1 depicts the Smart5Grid Functional Architecture which is logically divided into three distinct layers, briefly discussed as follows:

*   **Platform**: this layer provides the User Interface (UI) with the developers. The UI is the entry point of users to the Smart5Grid facility and consists also a web application that manages the authentication and authorization of users. Also, it provides access to the services of the exposed APIs of the Open Service Repository and the Validation & Verification (V&V) framework, which are the other components of the upper layer. The OSR enables 3rd Party developers and experimenters to register their Network Applications and Virtual Network Functions (VNFs) [28]. The V&V Framework realizes the testing process which provides guarantees on the correct performance of the Network Applications to the consumers. The Verification part specifically ensures that the Network Application packages and all its components are well formed and syntactically correct. The Validation part performs tests on live instances of Network Applications guaranteeing performance with the required levels [29].
* **NFV (Network Functions Virtualization):** The NFV/Telco layer contains the Management & Orchestration (M&O) Framework [30–31] and the NFV/Telco Infrastructure. The M&O Framework is responsible of managing the end-to-end lifecycle of a Network Application deployment and provides services to cover all aspects of the complete lifecycle including onboarding, instantiation, scaling and termination. The NFV/Telco infrastructure part is inseparable and equally important as the M&O Framework. It consists of the computing and the network infrastructure. The computing infrastructure deploys the software components in the form of containers that constitute a Network Application and can be centrally located or at the edge of the network in order to fulfill low latency requirements. Networking infrastructure consists of the telco network components in both the access/core domains, orcherstrated to meet demands of the Network Applications.

* **Energy:** The Energy Infrastructure layer is positioned at the bottom of the Smart5Grid architecture, containing the grid components that connect to the Network Applications. It is an equally important layer as the upper layer parts, composed of heterogeneous sets of devices from across the generation, transmission, distribution and consumption network segments. It may also contain other energy devices such as cameras and sensors which may provide measurements to the Network Applications. The Telco Network acts as an intermediary domain between the Energy part and the NFV Infrastructure where the Network Applications are placed.

<figure><img src="image_2.png" /><figcaption>Fig. 1. Smart5Grid Functional Architecture [27, 32]</figcaption></figure>

## 3 UC#4: Real-Time Wide Area Monitoring – Field Platform Implementations

The scope of UC#4 is the Real-Time (RT) Wide Area Monitoring (WAM) of the interconnection power flow between Greece and Bulgaria. This is achieved by leveraging the advantages that the 5G Telecommunication Networks provide. The monitoring process
is executed from the newly established Regional Security Coordinator (RSC) in Thessaloniki, Greece. The role of the RSC is to promote regional cooperation and to support the strengthening of the neighbouring power systems in the region. Towards this goal, the RT monitoring of power flows between the countries is of great importance.

The continuous expansion of the European high penetration rate of the Distributed Energy Resources (DERs) significantly increases the complexity of the power system thus making its RT operation and control functions difficult to handle. As the number of connected DERs increases, inverter-connected devices dominate, leading to lack of physical inertia. The lack of inertia results in significant variations in the Rate of Change of Frequency (RoCoF), resulting in critical changes in the dynamic behaviour of the system. This challenge makes the existence of a WAM essential for the stability of the entire interconnected European power system [33, 34]. WAM systems leverage the high accuracy of the PMUs combined with the ultra-low latency and high availability of modern telecommunication networks.

A Phasor Measurement Unit, also called as a PMU<fnref n="1" /> – or a synchrophasor – is a key tool used on electric systems to improve operators’ visibility into what is happening throughout the vast grid network [35–37]. A PMU is a device that measures a quantity called a phasor and it is considered as a most robust device that can enhance the observability of modern power systems [38, 39]. The data originating from several PMUs, placed in a wider area of monitoring are gathered by the Phasor Data Concentrators (PDCs) devices. Those concentrators are responsible for the synchronization of the measurements of the different PMUs according to their timestamp and the forwarding of the synchronized measurements to the next level PDCs. Several layers of PDCs intervene between the PMUs and the SCADA (Supervisory Control and Data Acquisition) system<fnref n="2" /> [40] of the transmission system operator (TSO). From the communication point of view, the PMUs and the PDCs are connected with optical fiber with each other ensuring that the data will arrive on time to the destination and that there will not be any security breach or data leakage. However, this architecture only permits central, predefined and cumbersome implementation of wide-area monitoring and control (WAMC) strategies, even if the PMU data can be used in a variety of combinations according to the grids graph [41]. In addition, the installation of a new PMU and its connectivity with the rest of the system is a costly and troublesome procedure for the TSO. Therefore it is essential to optimize the number and installation location of PMUs [37].

Wide-area monitoring protection and control [42] has been proposed to solve the problems and limitations of SCADA [43, 44]. Providing time synchronized data of power system operating states, Wide Area Monitoring Systems (WAMS) can play a crucial role in next generation smart grid protection and control. Such systems help secure efficient energy transmission as well as reliable and optimal grid management.

In a WAMS, the sensor nodes are the basic parts of the implementation of information sensing and communication. Compared to other wireless network, the WAMS

<footnote n="1">¹ PMU was first invented in Virginia Tech in 1988 to measure phasors of voltage and current, frequency and real/reactive power in real-time. PMUs have been continuously enhanced and are now deployed in substations.</footnote>

<footnote n="2">² The most common task of SCADA is the state estimation of the power grid, which depends on unsynchronized and slow measurements.</footnote>
is a specific application oriented network, which has characteristics of large size and dynamic topology. A WAMS usually uses a multi-level hierarchical communication network with reliability, RT responsiveness, scalability, and reliability, to integrate all these components together. The main component of WAMC is the PMU that can facilitate the RT computing and synchronized phasor measurement of voltage and current in a power grid [45]. PMUs can achieve precision and accuracy by using the Global Positioning System (GPS), which have precise reference timing signals. This timing is used to achieve the synchronized measurement of voltage and current phasors. PMU's utilization has increased rapidly to improve the monitoring of the power grid [46]. This process purely implicates for a new quality of insight into the dynamic behaviour of the electric power network and the corresponding values are increasing because of more dynamic requirements for the system caused by renewable power infeed such as wind, solar and energy trade.

To this part, the integration of 5G network can assist by ensuring the same network performance as the optical fiber in terms of low-latency, high-speed and zero data loss communication that previous generations of wireless networks could not offer [47]. Additionally, the virtualization and the edge computing that the 5G brings as an attribute [48], offer a new view of the possibility to deal with the PDC as a virtualized instance (vPDC) that can be deployed in any general purpose of the node instead of a monolithic and expensive device [49]. Smart5Grid tries to fill in this gap by proposing a flexible wide area monitoring framework based on the deployment of vPDC instances across the grid enabled by 5G communication channels. This framework envisions to provide a comprehensive view of the power grid's condition and allow the operators to take coordinated actions to prevent cascading failures and blackouts and drastically increase reliability and resilience of power grids [50].

<figure><img src="image_3.png" /><figcaption>Fig. 2. Smart5Grid-Field Platform Call Flow Diagram for UC#4</figcaption></figure>

Figure 2 depicts a high level overview of the field platform currently implemented for the integration of the PMUs through separate 5G NSA (Non-Standalone) networks [51]. One of the main challenges of this setup is the topology of the 2 PMUs involved, since they are placed in neighboring countries (i.e., in Greece and Bulgaria), served by COSMOTE and VIVACOM, respectively. The “Greek side of the Demo” is often
referred to the Network part connecting the Greek PMU with the edge/cloud Server in Sofia. Correspondingly, the "Bulgarian side of the Demo" is often referred to the Network part connecting the Bulgarian PMU with the edge/cloud server in Sofia. The Setup Diagram can be considered as a "zoom-in" in "Fig. 1-Smart5Grid Platform" highlighting in the *Energy* and the *NFV/Telco* domains.

The PMUs at each site "gather" online measurements such as voltage, current and frequency of the interconnected power systems and forward those readings to the 5G gateway routers through an Ethernet connection. The 5G gateway routers at each site are provided with 5G-enabled SIM (Subscriber Identity Module) cards from each network operator and have both successfully established 5G connectivity. Specific port forwarding configuration is programmed at each 5G gateway router so that forwarding the measurements to the edge/cloud server is successfully established. The involvement of 5G NSA communication networks from COSMOTE and VIVACOM ensures the critical low latency and high availability. On the edge/cloud server side at VIVACOM's premises in Sofia, Bulgaria, specific security configurations are established in order to allow the reception of the PMU measurements. The edge/cloud server hosts the virtual machine (VM) where the Kubernetes cluster with the Network Application is placed. Involved network components are briefly listed below:

**Interconnected Systems:** These are the power interconnection lines between the Greek TSO's (IPTO) substation in Thessaloniki and the Bulgarian TSO's (ESO) substation in Blagoevgrad.

**PMUs:** Both are located at the HV network between Greece and Bulgaria and the vPDC is connected by using 5G NSA networks, needed for this critical operation.

**5G NSA Networks:** For both sides of the intended Demo, networks of COSMOTE and VIVACOM shall be utilized, correspondingly. Site surveys have been performed to verify the availability of 5G Network Coverage. However, a "criticality" issue that has been faced is the lack of 5G Core Network (CN).

**International Carriers:** Various interconnection scenarios of the Greek site to the edge/cloud server at Bulgaria are currently under evaluation with respect to the network latency requirements. At the time of writing this paper, the optimal routing is considered as the "Roaming Scenario" which exploits the commercial 5G Network Roaming Agreement between COSMOTE and VIVACOM. In this scenario, a VIVACOM SIM card is connected at the 5G gateway router at the Greek side, thus forwarding related data through the international carriers to the edge/cloud server in Sofia. In this way it is achieved the "shortest travel" between Thessaloniki and Sofia.

**Edge/Cloud Server:** It is installed on the virtual machine at VIVACOM's cloud server in Sofia. It hosts the Network Application created for the RT WAM scenario. The VM hosts a Kubernetes cluster, managed by the Network Application Controller. The role of the Network Application is to collect the measurements from the PMUs and provide live monitoring of the wide area between the borders of Greece and Bulgaria to the TSOs [22]. It is composed of 3 Virtual Network Functions (VNFs):

(i) *Virtual Phasor Data Concentrator (vPDC) Service:* The vPDC receives and time-synchronizes phasor data from the two PMUs, to produce an RT, time-aligned
output data stream. The vPDC is to synchronize the measurements according to their timestamp, to be comparable to each other. The C37.118 protocol [52] will be used to collect data from the PMUs. The vPDC may also transmit the combined data to other applications which can perform the tasks of archiving, visualization or control. Upon successful reception of the PMUs' measurements, the vPDC performs data integrity checking and validation, by means of the data status flag and time quality of PMUs.

(ii) *Wide Area Monitoring (WAM) Service:* This service aims to present several status indicators and visualization features of the PMUs such as: a map indicating the device's current location; the device's name, address, model, serial number and firmware version; the nominal grid frequency (Hz) and the current reporting speed (fps); the phase diagram with voltage/current vectors displayed (updated in near RT); voltage magnitude and angle difference monitoring, derived from historical data.

(iii) *Advisory Service:* here the main task is to propose the remedial actions for RT operation to both TSOs. Additionally, it intends to provide advisory indications for RT operation to both TSOs and ex-post analysis provision in case of severe event occurrence in the grid.

# 4 Testing Strategy – Definition of FPVMs

A complete list of “Field Platform Validation Metrics” (FPVMs) is developed and presented as discussed below for the Scope of RT WAM. The choice of the Metrics and the Targeted Values is a task requiring combined effort from a variety of partners coming from different backgrounds, that is: Energy operators (TSOs), telco operators, ICT providers, research institutes and application developers. The term “FPVM” may be considered as a “hyper-set” of Key Performance Indicators (KPIs) consisting of: Core Network KPIs such as network latency; Application KPIs such as application packet loss, or; a combination of these such as closed loop latency [53].

The final choice of the FPVMs depends on three main factors. Firstly, they must satisfy the network requirements as they have been already elaborated during the works of Smart5Grid's D2.1 [54]. This has to be achieved with a clear statement on what enforcements the 5G Networks will offer to the intended UC#4. Secondly, a mapping between Network KPIs and Application KPIs has to be performed in order to provide newly formed FPVMs that “best describe” the field implementations features. Thirdly, the availability of resources to measure the metrics on field; the latter, is a particularly crucial factor, since 5G commercial networks are utilized for the Greek and Bulgarian sides of the scheduled demos. This imposes significant constraints regarding the
live measurements as expected to be available from the involved Telco Operators. The FPVMs for RT Wide Area Monitoring are as follows:

**Network Latency** (in msec): Total time required for the PMU measurements to reach the vPDC service (i.e., the absolute waiting time for the vPDC to receive the measurements) [44]. A targeted value is of <40.

**End-to-End (E2E) Latency** (in msec): E2E latency, or one trip time (OTT) latency, refers to the time it takes from when a data packet is sent from the transmitting end to when it is received at the receiving entity. A targeted value is of <200.

**Closed Loop Latency** (in msec): It consists of the E2E Latency in addition to the time the TSOs are notified of a possible fault in the power network.

**Delay Jitter** (in msec): It is a measure of the variation in latency over time. A targeted value is of 5, approx.

**Application (vPDC) Packet Loss** (in %): It refers to packets not reaching their destination after being discarded by the vPDC component. (Targeted value: <0.1).

**Communication Service Availability** (in %): It is the amount of time the E2E application is properly delivered according to the specified performance metrics, over the amount of time that is expected to deliver the E2E Network Application [54]. A targeted value is of >99.999%.

**Communication Service Reliability** (in %): Reliability is defined [54] as the percentage value of the amount of sent network layer packets successfully delivered to a given node within the time constraint required by the targeted service, divided by the total number of sent network layer packets. A targeted value is of >99.999%.

Device Density (in devices/km): It is the maximum number of PMU devices per unit area under which the specified reliability should be achieved [54]. A targeted value is 1.

# 5 Overview

The adaptation of 5G networks is an important enabler for the development of smart grid technologies. In particular, 5G supports inclusion of many innovative features also including network slicing for the provision of specific services tailored to specific needs. The Smart5Grid project is a modern research initiative facing such challenges and serving dedicated energy verticals upon the consideration of a modern architecture. Our work is structured around one specific use case dealing with RT WAM of the interconnection power flow between Greece and Bulgaria. More specifically, we assess the important role performed by PMUs in parallel with 5G NSA networks upon a roaming-based scenario and then we discuss the related field platform implementations by assessing the roles of the involved networks components. To facilitate future trials we also define a set of KPIs under the term "Field Platform Validation Metrics" giving a complete performance overview of the field implementations and we set corresponding targeted values.

**Acknowledgments.** This work has been performed in the scope of the *Smart5Grid* European Research Project and has been supported by the Commission of the European Communities /5G-PPP/H2020, Grant Agreement No.101016912.
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