Wireless Field-area Networks for Smart Grid Communications

by Bert Williams, ABB Tropos Wireless Communication Systems

From the executive suite to linemen in the field, utilities and their employees are coming under increasing pressure from various stakeholders.

Shareholders, regulators, politicians, customers and consumer and environmental advocacy groups all push frequently conflicting agendas: Lower rates; Encourage conservation; Increase earnings and dividends; Improve reliability; Reduce emissions; Integrate renewable generation sources; Implement net metering; Fill the imminent labor gap. These are but a few utility challenges.

“Smart grid” is an overused, ill-defined catch phrase, but the term conveys an important concept.

Software applications installed in operation and control centers, specialized computers and software in substations, plus intelligent electronic devices (IEDs) and other smart apparatuses in substations and along distribution feeders can implement a comprehensive smart grid application portfolio.

A smart grid portfolio can include various distribution automation applications, including fault detection, isolation and restoration/fault location isolation and service restoration (FDIR/FLISR), active volt/VAR management and conservation voltage reduction (CVR), substation automation and advanced metering infrastructure (AMI).

Additional applications can be enabled by equipping field-workers with laptops, tablets and handheld computers.

Smart grid applications can help utilities meet conflicting demands.

An additional component is required to implement a smart grid system: a two-way broadband communication network (see Figure 1). The communication network links people and devices in the field with software at substations and the utility’s operations and control center, enabling vast improvements in efficiency, security, reliability and resiliency.

fig. 1

Figure 2 shows a typical utility communication network architecture and how the communication network relates to components of the electricity distribution system.

fig. 2

Field-area Network Requirements

Field-area networks (FANs), represented by the dashed, light blue lines in Figure 2, fill the communication gap between the core Internet Protocol (IP) network and devices, as well as personnel, in the field.

FANs most often are implemented with wireless networking technologies because their large geographic coverage areas, many connected devices and the need to support mobile field-workers make them technically and economically infeasible to implement using wired technologies.

Wireless networking technologies used in FANs include cellular, narrowband point-to-multipoint (PTMP), broadband PTMP and broadband wireless mesh networks.

To support a portfolio of smart grid applications, FANs must meet these requirements:

High reliability. Communications are most critical during outages. FANs must operate even when events disable the electric grid.

Ideally, the wireless network will incorporate cognitive radio software that can, for instance, automatically route around interference, failures and congestion. Individual communication devices must be ruggedized, be weatherized and supply battery backup.

Scalable. Field-area communication networks must scale to cover large geographic areas-potentially a utility’s entire service territory.

They also must scale to support, directly or via neighborhood-area networks (NANs), millions of connected devices. Conversely, because utilities may roll out smart grids incrementally, FANs must be economical to implement on a small scale, say, at a single substation or along a single distribution feeder.

High performance. As IEDs and other intelligent field devices proliferate, become smarter and gather more information, higher-capacity networks are required because more applications and devices use the FAN and they send and receive more data. Additional capacity also is required to support mobile work force applications.

Many applications in the distribution system are not latency-sensitive; however, the few that are, including protection and safety applications, are critical.

Because a unified FAN must support the requirements of all deployed applications, low latency is essential.

Secure. Like all networks, wireless FANs come with potential vulnerability to cyberattacks.

In IP-based FANs, this challenge can be met by implementing a multilayer, defense-in-depth security architecture using enterprise tools and techniques.

Mobility. Providing communications for field crews requires that the FAN support mobility.

Multiapplication. It may seem a tautology that a network that can support many applications must offer multiapplication support; however, supporting multiple applications drives some specific technical requirements such as the need to provide virtual local-area networks (VLANs) and quality of service (QoS).

Flexible. To support the widest variety of applications and devices, the FAN must be built on industry standards such as TCP/UDP/IP, 802.11 (Wi-Fi) and 802.3 (Ethernet).

To best integrate legacy field devices and avoid stranded assets, the FAN also must support secure network connections to devices that use serial links and automation protocols.

Field-area Communication Network Technology Choices

Numerous wireless technology choices exist for implementing FANs (see Figure 3); however, when the characteristics of these technologies are compared to FAN requirements, broadband wireless mesh networks supplemented by broadband PTMP links when needed best meet the requirements.

fig. 3

Broadband wireless mesh networks offer the following characteristics:

Highly available. Wireless mesh networks provide high availability by automatically selecting the best route through the network from multiple radio frequency (RF) paths, channels and bands.

To withstand extremes in climate, mesh routers are available with extended operating temperature ranges, enhanced wind survivability and housings fabricated using specialized alloys and plating.

Scalable. Broadband wireless mesh networks have been proven to scale to large coverage areas (3,000 square miles in Abu Dhabi), massive volumes of data (1 TB of data transferred daily in Ponca City, Oklahoma), many machine-to-machine (M2M) endpoints (more than 1 million electricity and water meters in Abu Dhabi) and many routers (more than 3,000 routers’ operating in the network in Abu Dhabi).

Because mesh networks generally don’t require tower construction, they also can cover small areas such as a single distribution feeder economically.

High capacity and low latency. Broadband wireless mesh networks can provide greater than 10 Mbps of throughput at each mesh router with latency of less than 1 ms per mesh hop.

Secure. Broadband wireless mesh networks can implement a multilayer, defense-in-depth security architecture using open security standards.

Using a multi-layer, defense-in-depth approach with standards-based tools, wireless mesh networks have attained FIPS 140-2 compliance and are compatible with NERC CIP v5, NISTIR 7628 and IEC 6235.

Mobility. Broadband wireless mesh networks provide seamless, session-persistent roaming at vehicular speeds within the coverage area.

Clients, including those that have established an IPsec/VPN connection, can move between router and IP subnets without losing connections.

VLANs/application QoS. Broadband wireless mesh networks support VLANs and QoS. VLANs enable traffic from different applications and user groups to be segregated.

Flexibilty/interoperability/open standards. Broadband wireless mesh networks support open standards including TCP/UDP/IP, 802.11 (Wi-Fi) and 802.3 (Ethernet). They can interoperate with other standards-based smart grid components. To integrate legacy field devices and avoid stranded assets, some mesh routers support secure network connections to devices that use serial links and automation protocols such as DNP-3 and IEC 61850.

Conclusion

Communication networks are a key component to smart grid implementation. Utilities that are implementing smart grid communication networks generally use a multitier network architecture. Many wireless technology choices are available for FANs. When comparing the capabilities of these technology choices with FAN requirements, broadband wireless mesh networks supplemented by broadband PTMP links when necessary provide the best match to the requirements.

Bert Williams is director of global marketing for ABB Tropos Wireless Communication Systems. He brings 30 years of experience in leading the marketing organizations of networking companies. He has a Bachelor of Science with University Honors in Electrical Engineering from Carnegie Mellon and an MBA from Harvard Business School. Reach him at bert.williams@nam.abb.com.

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