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Assessment of Communication Technologies and Network Requirements for Different Smart Grid Applications Murat Kuzlu, Member, IEEE and Manisa Pipattanasomporn, Senior Member, IEEE Virginia Tech – Advanced Research Institute, Arlington, VA 22203

Abstract— Our current electric power grid was built over 100 years ago based on simple demand and supply requirements. With emerging technologies, availability of small-scale distributed energy sources and higher customer expectations, two-way information flow, communication architecture, as well as smart sensing and metering technologies are being incorporated into the current power grid. The objective of this paper is to compare different communication technologies and assess their suitability for deployment to serve various smart grid applications. Both wired and wireless communication technologies are compared in terms of their data rates and coverage ranges. Comprehensive assessment is performed to evaluate suitability of different communication technologies for use to enable different smart grid applications based on specific network requirements.

Index Terms—Smart grid, communication technologies, two-way communication, smart grid applications and network requirements.

I. INTRODUCTION

T

HE U.S. electric power infrastructure was designed using 20th century technologies [1]. Encountering situations have shown that there is a need to make the current power grid more reliable, resilient, secure, and efficient. Hence, the concept of smart grid introduced by the Department of Energy (DOE) known as the modern grid has emerged [2]. In the smart grid environment, various energy services, i.e., demand response, load management, distribution generation, real-time pricing, automatic meter reading (AMR), advanced metering infrastructure (AMI), and substation automation, are served by incorporating advanced information technologies and intelligent communication networks with legacy power systems. A smart grid is a complex network of networks that comprises both electrical and cyber infrastructures and several thousands of intelligent electronic devices (IEDs), wired and wireless sensors, smart meters, distributed generators and controllable loads. Communication networks play a crucial role to enable smart grid implementation and manage these devices by providing two-way data communications between a utility and end-use devices. The complexity of a smart grid may lead to difficulties in building its communications network as many parameters and different requirements must be taken into account. In [3], authors proposed a communication network model for smart grids by taking into account application requirements, link capacity and traffic settings. In [4, 5], This work was supported in part by U.S. National Science Foundation under Grant IIP-1114314. M. Kuzlu and M. Pipattanasomporn are with Virginia Tech – Advanced Research Institute, Arlington, VA 22203 USA (e-mail: [email protected]; and [email protected]).

978-1-4673-4896-6/13/$31.00 ©2013 IEEE

authors proposed a heterogeneous communication architecture for smart grids with detailed analysis of communication requirements. The design of communication network architecture is crucial to provide a reliable, flexible, affordable, and sustainable power grid. It should meet the specific requirements, i.e., reliability, latency, availability, security bandwidth, and priority, depending on applications. For example, latency requirements are less than 20 milliseconds for synchrophasor applications; and less than 200 milliseconds for most smart grid supervisory control and data acquisition (SCADA) [6]. In [7], authors proposed a mesh radio-based solution, which is a low-cost, scalable, self-organizing, for smart metering applications, while in [8], authors proposed wireless communication technologies for demand management. Although existing wired and wireless communication technologies can be applied to the smart grid, establishing smart grid standards and protocols is an urgent issue for some devices, i.e., smart meters [9]. In the literature, smart grid technologies and standards are discussed to provide an overview of the smart grid paradigm and integration of different communication technologies [10, 11]. Some studies focus on a specific standard or communication technologies, i.e., smart metering [12], power line communication (PLC) [13], and wireless communication [14, 15]. The objective of this paper is to compare various communication technologies both wired (i.e., fiber optic, DSL, coaxial cable, PLC) and wireless (i.e., ZigBee, WLAN, wireless mesh, Z-Wave, WiMAX, cellular and satellite), and evaluate their suitability for deployment in a multitude of smart grid applications. This evaluation is based on specific network requirements for different smart grid applications. The rest of this paper is organized as follows. Section II provides an overview of the smart grid communication network architecture. Section III discusses and compares various communication technologies that can be deployed in the smart grid environment. Section IV discusses network requirements for different smart grid applications and provides assessment of communication technologies that are suitable for deployment to enable these applications. II. SMART GRID COMMUNICATION NETWORK ARCHITECTURE Communication infrastructure in the smart grid environment can be presented using a hierarchical multi-layer architecture, as shown in Fig. 1. This three-layered architecture comprises: wide area network (WAN), neighborhood area networks (NAN)/field area network (FAN) and customer premises area network. Data rate and communication range requirements of each layer are summarized in Fig. 2.

for smart metering applications is greater than 100 kbps depending on meter data size and the number of meters. NANs can be implemented over various communication technologies, including ZigBee, WLAN, PLC, as well as long distance wired and wireless technologies, such as cellular and data over cable services interface specification (DOCSIS). C. Customer Premises Area Network Fig. 1. The hierarchical multi-layer architecture of smart grid communications.

Fig. 2. Date rate and communication range requirements for smart grid communications hierarchy.

Each layer is discussed below: A. Wide Area Network Wide area network (WAN) provides communication links for smart grid backbones; and covers long-haul distances from a control center to NAN/FAN. When a control center is located far from substations or end customers, real-time measurements obtained at the substation level are delivered to the control center (or control commands from control centers are delivered to the electric devices) through WANs. WANs also enable communication with automation and distribution devices, including SCADA, remote terminal unit (RTU), phasor measurement unit (PMU), and other sensors. This is to allow management and control of various devices and provide a range of services, such as substation automation, field devices automation, metering, billing, outage management, demand response and load management. WAN can be implemented over various communication technologies such as fiber, power line, and wireless media using cellular. Optical communication is most commonly used as a communication medium between transmission/distribution substations and a utility control center due to its high capacity and low latency. Cellular and WiMAX can also be used due to their wide coverage range and high data throughput. B. Neighbor Area Network/Field Area Network Neighborhood area network (NAN) manages information flow between WANs and customer premises area networks using either wireless or wired communications. It supports energy data collection from customers in a neighborhood to a utility company. NAN can also be called Field Area Network (FAN). NAN/FAN enable a range of smart grid applications, such as smart metering, load management, distribution automation, or others customer-based applications [16]. Coverage area and data rate requirements for NAN can vary depending on applications. For example, data rate requirement

Customer premise area networks can be classified as home area network (HAN), building area network (BAN) and industrial area network (IAN), depending on the environment, i.e., residential, business, and industrial. They enable communication between NAN/FAN and end-use devices such as appliances and sensors on the customer side. HAN usually enables communications with an electric utility for residential or small-business consumers. BAN and IAN are considered a more complex combination of specialized local area networks, building management software, and connected controls/ devices. They enable commercial or industrial consumers for connections with an electric utility [17]. Customer premises area network communicates with various smart devices, e.g., appliances, energy management stations, energy sources, and connects with a utility network via smart meters or other devices (e.g., concentrators). It supports various energy services, i.e., prepaid, user information messaging, demand response, load control and real-time pricing, for utilities and customers. Main communication requirements for customer premises network are low power consumption, low cost, simplicity, and secure communication. Various wired and wireless communication technologies i.e., ZigBee, WLAN, Z-Wave, PLC, have been introduced for customer premises area network. These technologies are discussed in the next section. III. VARIOUS COMMUNICATION TECHNOLOGIES FOR THE SMART GRID The comparison of various communication technologies for the smart grid in terms of its data rate and coverage distance is presented in Table I. The technology description and their pros/cons are discussed below. A. Wired Communication 1) Fiber-Optic Communication is one of the fundamental communication technologies for WANs due to its high data rate and immunity to noise. There are various forms of fiber communication such as Passive Optical Network (PON), Wavelength Division Multiplexing (WDM), and Synchronous Optical Networking (SONET)/Synchronous Digital Hierarchy (SDH). The form of fiber communication to be selected will depend on applications, which is based on response times and quality of services that the network can deliver. • PON is a point-to-multipoint network architecture, which utilizes optical splitters to enable a single optical fiber to serve multiple customers. • WDM is an effective technology to exploit bandwidth capacity available in optical fiber. Multiple wavelengths are used to carry several data streams simultaneously over the same fiber in WDM networks.

• SONET/SDH is a time-division multiplexing (TDM) architecture that was designed to carry high capacity traffic. SONET and SDH are essentially the same standard: SONET in the U.S. and Canada, and SDH in the rest of the world. Fiber-optic communication is frequently used to provide backbone communications supporting various smart grid applications, such as substation automation and transmission domain communication. It offers high data rates, i.e., 5, 10, 20 or 40 Gbps, and therefore, can easily support high-speed data transfer for long distance. Optical fiber-based communications provide a long-term solution for the smart grid. However, they can be costly due to their high upfront investment and maintenance costs. TABLE I. COMPARISON OF COMM. TECHNOLOGIES FOR THE SMART GRID Max. Theoretical Standard/ Protocol Data Rate Wired Communication Technologies Fiber-Optic PON 155Mbps -2.5Gbps WDM 40 Gbps SONET/SDH 10 Gbps DSL ADSL 1-8 Mbps HDSL 2 Mbps VDSL 15-100 Mbps Coaxial Cable DOCSIS[18] 172 Mbps PLC HomePlug 14-200 Mbps Narrowband 10-500 kbps Wireless Communication Technologies ZigBee ZigBee 250 kbps ZigBee Pro 250 kbps WLAN 802.11x 2-600 Mbps Technology

Wireless mesh

Z-Wave WiMAX Cellular

Satellite

Various (e.g., 802.11, 802.15, 802.16) Z-Wave 802.16 2G 2.5G 3G 3.5G 4G Satellite Internet

Coverage Range up to 60 km up to 100 km up to 100 km up to 5 km up to 3.6 km up to 1.5 km up to 28 km up to 200 m up to 3 km up to 100 m up to 1,600 m up to 100 m

Depending on selected protocols

Depending on deployments

40 kbps 75 Mbps

up to 30 m up to 50 km

14.4 kbps 144 kbps 2 Mbps 14 Mbps 100 Mbps 1 Mbps

up to 50 km

100-6,000 km

2) Digital Subscriber Line (DSL) is a digital data transmission technology on ordinary telephone lines. There are three DSL systems: • Asymmetric DSL (ADSL) provides different data rates in two directions, downstream at up to 8Mbps and upstream at up to 800 kbps [19]. • High speed DSL (HDSL) systems support data rate of up to 2.048 Mbps over a distance of 3.6 km. • Very high data rate DSL (VDSL) is a DSL technology providing faster data transmission, i.e., 100 Mbps. DSL is suitable for providing aggregation services for data transmission between homes and an electric utility. It is already available to a large number of premises based on existing telephone services. Therefore, DSL can be a good candidate for smart grid projects, supporting smart metering

operation. However, DSL efficiency will reduce depending on distance. This makes the service unreliable for customers who are away from the provider. As a result, DSL will not be suitable for critical smart grid applications due to its low reliability and potential down time issues. 3) Coaxial Cable is a high-speed data transfer technology that relies on cable television infrastructures. Similar to DSL, coaxial cable provides network-edge connectivity from a provider to end users. Coaxial cable networks were mainly designed for broadcast services, i.e., television and radio channels. Data Over Cable Service Interface Specification (DOCSIS) is an international coaxial cable communication technology that provides high-speed data transfer over existing hybrid fiber-coaxial (HFC) infrastructure. In the smart grid environment, coaxial cable communication can serve as a communication link between home devices, e.g., smart meters, and an electric distribution company, as well as for home automation services, home security and in energy management systems. Its drawback is that the entire bandwidth is shared along the line among many customers. Therefore, the increasing number of customers makes the connection slow. 4) Power line communication (PLC) is a wired communication technology that enables data transmission over existing power lines. This technique injects a high frequency carrier into power lines and modulates the carrier with the data to be transmitted. PLC is a very good candidate for many command and control applications including energy management, smart metering, home/building automation, switching and lighting, HVAC control, street light control and more. It is suitable for smart grid applications in rural areas that do not have other existing communication infrastructures. PLC is a cost effective technology due to the use of existing power grid infrastructure. However, it has significant technical issues such as its inability to transmit signals cross a transformer(s), power line channel distortion, interference, noise, harsh conditions of the power line environment, and security concerns. B. Wireless Communication 1) ZigBee is a wireless personal area network protocol based on the IEEE 802.15.4 standard. It operates on the unlicensed ISM (industrial, scientific and medical) bands: 868 MHz in Europe, 915 MHz in the U.S., and 2.4 GHz worldwide. Its data rates range from 20kbps to 250kbps, that is: 250kbps at 2.4GHz, 40kbps at 915MHz, and 20kbps at 868MHz. ZigBee provides coverage distance of up to 100 meters, while ZigBee Pro provides coverage distance of up to 1,600 meters. ZigBee is widely used for home/building automation, energy monitoring, industrial plant management, as well as AMI applications [10]. It supports various network topologies such as star, tree and mesh topologies, as well as a robust security layer with 128-bit AES encryption [20]. Although ZigBee is a cost-effective, low-power, highefficiency and secured wireless communication technology, it supports short-range data transmission, and provides low data speed. It is therefore suitable for in-home applications. Additionally, ZigBee faces severe interference problems in the presence of various networks due to sharing same channel spectrum with some protocols such as WiFi.

2) Wireless Local Area Network (WLAN) is a high-speed wireless Internet and network communication technology, which is commonly known as Wi-Fi. It is based on the IEEE 802.11 series of standards including 802.11, 802.11a, 802.11b, 802.11g and 802.11n. WLAN operates in 2.4 GHz, 3.6 GHz and 5 GHz unlicensed ISM frequency bands. The IEEE 802.11x standards specify data rates from 2 Mbps to 600 Mbps, and the coverage range of up to 100 meters. WLAN communication is another promising alternative for HANs and NANs. WLAN provides reliable, secure and high-speed communications. However, it supports short-range communications (i.e., up to 100 meters). The cost and power consumption of WLAN products are also higher than other short-range wireless technologies such as ZigBee and Z-Wave. 3) Wireless Mesh is a cost-effective, robust and flexible wireless network which consists of many nodes including mesh clients and routers. In a wireless mesh network, each node can act as a signal repeater and automatically route messages from one node to another. This is known as dynamic routing. Additionally, when one node can no longer operate, the rest of the nodes can still communicate with each other, directly or through one or more nodes. A wireless mesh network can provide a wide coverage range due to its ability to perform multi-hop routing. While a traditional wireless network may spread throughout a building or a neighborhood, a wireless mesh network can cover a much larger area, such as a city. Mesh networks can be implemented with various wireless technologies, i.e., 802.11, 802.15 and 802.16. Since wireless mesh networks have the advantage of being easy to implement, cost-effective, extend and automatically self-healing, they are becoming a key technology to serve many smart grid applications, such as AMI and home automation. They however cannot provide a high-speed data transfer, and suffer from interference generated by the other wireless devices. 4) Z-Wave is a reliable, low-power, low-cost proprietary wireless technology that is suitable for short-range communications. It operates in the 900 MHz ISM. It supports data rate of up to 40 kbps and the coverage distance of up to 30 meters. Z-Wave is designed specifically for remote control applications in residential and light commercial environments. It can be applied to smart grid applications in HANs. Z-Wave supports mesh networks, which makes it a good candidate for HANs. However, it provides short-range communications and has low data transmission rate. 5) WiMAX is a 4G wireless technology based on the IEEE 802.16 series of standards, i.e., IEEE 802.16-2004, 802.16e, for Metropolitan Area Networks (MAN). WiMAX operates in the 2.3, 2.5, 3.3, and 3.5 GHz frequency bands, as well as the unlicensed 5.8 GHz band. It provides data rates of up to 75 Mbps with a coverage distance of 50 km, and has low latency (10-50 ms). The WiMAX standard natively supports quality of service and real-time two-way broadband communications between nodes. This makes WiMAX a good candidate for smart grid applications. WiMAX networks can be used for applications such as monitoring transmission and distribution processes, and smart metering. WiMAX is a high speed, reliable and long distance wireless technology. It can serve hundreds of users with a single base

station. However, WiMAX is expensive and requires high power consumption. Its performance can also be affected by bad weather conditions. 6) Cellular is a radio network that uses a large number of transmitters to create cells. Cellular systems allow reusing frequencies to increase both coverage and capacity. Telecommunications industry divides cellular technologies into four generations that are labeled 1G, 2G (GSM), 3G (UMTS), and 4G (WiMAX and LTE) with intermediate versions labeled 2.5G (GPRS and EDGE) and 3.5G (HSPA). Cellular systems commonly operate in 850, 900, 1800, and 1900 MHz frequency bands. Cellular networks can enable smart metering deployments spreading to a wide area environment. Existing cellular systems can be a good candidate to provide communication between smart meters and a utility and between far nodes. In summary, 3/4G cellular is a high-speed, low latency, secure and long distance wireless communication technology. Availability of existing cellular communication infrastructure provides fast installation and cost-effectiveness. However, start-up costs of service providers and consumers for equipment upgrades are high. Additionally, cellular services are shared with mobile customers, which may lead to congestion and reduction the network performance. 7) Satellite Communication is a wireless communication technology for transferring signals between two nodes using a satellite. This is also known as space communication. In satellite communication, the modulated signal is sent towards the satellite. Then the satellite amplifies the signal and sent it back to the receiver on the earth’s surface. It provides a global coverage between any pair of communication nodes, and provides date rate of up to 1 Mbps. Satellite communication can be used to support remote monitoring of transmission and distribution substations and provide GPS-based location and synchronization of time. Satellite communication is the only method that can provide connectivity to areas where wired and wireless communications are not available. However, signals can be affected by severe weather conditions and suffered from long round-trip delays. IV. NETWORK REQUIREMENTS FOR VARIOUS SMART GRID APPLICATIONS Specific network requirements for major smart grid applications in terms of their data rate, latency, reliability, coverage range, and security requirements are summarized in Table II. These requirements vary from applications to applications, and will influence choices of communication technologies selected. For home/building automation applications, communication technologies with low data rate and short coverage distance (i.e., ZigBee, WLAN, Z-Wave and PLC) are sufficient to enable energy management functions within customer premises area networks. For applications in NAN/FAN (e.g., smart metering, load management and distribution automation), communication technologies that support higher data rate and larger coverage distance (up to 10km) than those for customer premises area networks are required. These are DSL, coaxial cable, wireless

mesh, WiMAX and cellular. PLC has also been deployed for selected smart metering applications in the U.S. To determine data rate requirements for smart metering applications, meter data sizes, the number of customers served, and latency requirement must be taken into account. For example, for ondemand meter reading applications, a typical meter message size is 100 bytes with latency requirement of less than 5 seconds [21]. In this case, if we assume that the utility inquiries 625 smart meters per concentrator in a neighborhood, the required data rate would be more than 100 kbps (i.e., 100bytes * 8bits/bytes * 625 / 5sec  100 kbps). For non realtime meter reading applications, i.e., multi-interval meter readings, meter data are collected multiple times per day. With reading frequency of 4-6 times per day, a typical message size can range from 1,600-2,400 bytes per reading interval, assuming that the meter records energy data every 15-minute intervals (i.e., 100bytes/message * 4messages/hour * 46hours/reading interval = 1,600-2,400 bytes/reading interval). Latency of several hours is acceptable for such multi-interval meter reading applications. For load management applications, e.g., direct load control, data rate requirements will depend on the number of customers participating in load control programs. If we assume that 500 customers participate in a load control program, and each message is of 64 bytes in size with at most 5-second latency requirement, the required data rate would be more than 50 kbps (i.e., 64bytes * 8bits/bytes * 500 / 5sec  51.2 kbps). For distribution automation (DA) applications – which allow a utility to send configuration and control commands to remote field devices (e.g., capacitor banks, sensors, reclosures, switches, and voltage regulators), a typical control message

size is 150-500 bytes. With the most stringent latency requirement of less than 1 second per message and the assumption that there are 15 such field devices to control (this is a typical number of devices per 1000 meters), the required data rate would be greater than 18kbps (i.e., 150bytes * 8bits/bytes * 15 / 1sec  18kbps). For applications in WAN (e.g., synchrophasor, backhaul/ core/metro networks), communication technologies that support much higher data rate and can provide long coverage distance (up to 100 km) are required. In this case, fiber optic, WiMAX and cellular can serve this purpose. Satellite communications can also be used to provide redundant communications at critical transmission/distribution substation sites as backup a communication mean. To determine data rate requirements for synchrophasor applications, the number of PMUs in the system, its message size and sampling frequency should be known. There are currently several hundred PMU’s already deployed across the North American grid [22]. With the assumption that PMUs provide measurements as often as 60 times per second and there are 100 PMUs with the message size of 48 bytes are installed in a system, the required data rate would be greater than 2 Mbps (i.e., 48bytes * 8bits/bytes * 60times/sec * 100  2,304 kbps). Backhaul and core/metro networks require even much higher data rate at least 10 Mbps. With respect to reliability and security requirements, high reliability/security is required for home/building automation, metering, load management and distribution automation applications; and very high reliability/security is required for synchrophasor and backhaul/core/metro network applications.

TABLE II. NETWORK REQUIREMENTS FOR MAJOR SMART GRID APPLICATIONS AND COMMUNICATION TECHNOLOGIES THAT CAN MEET THE REQUIREMENTS

HAN/BAN/ IAN NAN/ FAN

WAN

Home/building automation On-demand meter reading Multi-interval meter reading Load management Distribution automation Synchrophasor Backhaul/core/metro networks

High

High

Up to 100m

>100 kbps

< 5 sec

>50 kbps >18 kbps > 2 Mbps

< several hours < 5 sec < 1 sec < 20 ms

>10 Mbps

< 50 ms

>100 kbps

High

Very High

High

Very High

X X X X

Up to 10km

100 km or more

Cellular Satellite

< minutes

WiMAX

< 100 kbps

Wireless Mesh

Coverage range

Z-Wave

Security

WLAN

Reliability

ZigBee

Latency

PLC

Data rate

Coaxial Cable

Application

DSL

Network

Fiber Optic

Communication technologies Wired Wireless

X X

X X X

X X X

X X X

X X X

X X X X

X X X X X X X X X X X

V. CONCLUSIONS Communication networks are important components of the smart grid to enable improvement in system reliability, efficiency and security. This paper compares different wired and wireless communication technologies and identifies their suitability to enable selected smart grid applications, ranging from the enterprise level, generation, transmission and distribution levels, to the end customer level. Communication technologies under discussion are both wired solutions (i.e., fiber optic, DSL, coaxial cable, and PLC), and wireless solutions (i.e., ZigBee, wireless mesh, WLAN, Z-Wave, WiMAX, cellular, and satellite), which are compared in terms of their data rates and coverage ranges. Network requirements for various smart grid applications -- based on data rate, latency, reliability security, and coverage distance -- are also discussed. As wireless technologies provide lower installation cost, more rapid deployment, higher mobility and flexibility than its wired counterparts, wireless technologies are recommended in most of the smart grid applications. It is expected that this paper will benefit student researchers and engineers who work in related fields by providing an insight into various technologies that can enable two-way communications in the smart grid environment. Additionally, comprehensive assessment as presented in this paper will enable reasonable technology selections for various smart grid applications and deployments. VI. REFERENCES [1]

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VII. BIOGRAPHIES Murat Kuzlu (M'11 - IEEE) joined Virginia Tech's Department of Electrical and Computer Engineering as a post-doctoral fellow in 2011. He received his B.Sc., M.Sc., and Ph.D. degrees in Electronics and Telecommunications Engineering from Kocaeli University, Turkey, in 2001, 2004, and 2010, respectively. From 2005 to 2006, he worked as a Global Network Product Support Engineer at the Nortel Networks, Turkey. In 2006, he joined the Energy Institute of TUBITAK-MAM (Scientific and Technological Research Council of Turkey - The Marmara Research Center), where he worked as a senior researcher at the Power Electronic Technologies Department. His research interests include smart grid, demand response, smart metering systems, wireless communication and embedded systems. Manisa Pipattanasomporn (S'01, M'06 - IEEE) joined Virginia Tech's Department of Electrical and Computer Engineering as an assistant professor in 2006. She manages multiple research grants from the U.S. National Science Foundation, the U.S. Department of Defense and the U.S. Department of Energy, on research topics related to smart grid, microgrid, energy efficiency, load control, renewable energy and electric vehicles. She received her Ph.D. in electrical engineering from Virginia Tech in 2004, the M.S. degree in Energy Economics and Planning from Asian Institute of Technology (AIT), Thailand in 2001 and a B.S. degree from the Electrical Engineering Department, Chulalongkorn University, Thailand in 1999. Her research interests include renewable energy systems, energy efficiency, distributed energy resources, and the smart grid.