All Utilities are going through major changes with the addition of large scale communication networks to permit interconnectivity to devices on their grids. A wide variety of devices are being connected. Of course, the most popular device is the residential smart meter. But, now Utilities are thinking beyond these initial meter deployments and are adding traffic from Corporate and Industrial (C&I) meters to these networks too. Smart grid devices such as power line meters, transformer meters, reclosers, segmentation switches, tie switches, solar arrays, wind farms, and cap banks are all common new additions to the communications network too. Until now, we have had to depend upon our meter vendors to provide the communication networks for these tasks. The problem is that these vendor specific networks have been based on closed architecture that was propriety to specific vendors. This locked the Utility into the one vendor solution and forced future procurement decisions. As well, some of these networks worked well for simple tasks like residential meter reading, but failed to perform for more demanding tasks like C&I requirements, renewable energy, smart cars, and smart grid connections. A different approach is necessary for Utilities to move forward with confidence that the networks they buy today can support their needs and applications over the longer term.
The smart grid is now moving from its infancy and maturing to the next early stage of its lifecycle with the advent of open architecture and standards based networks. This next step in the maturation process is critical to long-term dependability and performance for the new smart grid applications. Various groups have been developing standards to support these Utility needs. An example are the IEEE 802.15.4g and 802.25.4e protocols. Another example is the Internet Engineering Task Force’s (IETF) 6LowPAN standard which drives the IETF IPv6 standard to the Internet of Things (IoT) network. Interoperability is coming to these standards with the introduction of the evolving industry driven Wi-SUN (Wireless Smart Utility Network) standard that promises interchange between vendors. Utilities are anxiously awaiting these standards to be included into smart grid products. Once available, they can have the single vendor shackles removed from their purchasing process, thereby allowing an open multi vendor business model that provides robustness, cost effectiveness, enhanced support, and most of all, trust and confidence to these emerging smart grid networks. While some vendors resist this advancement, others embrace it so it is moving forward, albeit not as fast as we would like to see.
It needs to be stated that adoption of standards has benefits and disadvantageous. With a standard, comes vendor interchange. This is a huge advantage. But, what we lose at times is true innovation and some unique, vendor specific features and capabilities that are not included within the standards. Some vendors see their unique innovations as a competitive edge and a differentiator in the selling process. However, this is out of date thinking, it is unwise to hold your cards so close to your chest in a global economy. Today, it is much smarter to get your innovation adopted within the standards and then cross license the rights to the standard. This business model protects your intellectual capital. Open model revenues from licensing can far outpace monies earned from direct sales in a closed model. Some industries, such as the IT world have awoken to this modern approach, yet sadly the smart grid vendors have not embraced it across the industry. But there are a few fine exceptions. Vendors with protectionist attitudes should learn from past lessons; remember the Betamax versus VHS video tape wars, which business model won the day there? The open model, of course. Nothing has changed since those days; Utilities desire options for mass market commodities and expect interoperability, advanced features and the lowest cost per unit. This can only be achieved from a standards based business model.
Figure 1 – Federated Model
The Internet of Things supports several architectural models, unlike other networks that typically support just one model. The IoT can use a centralized, distributed, or federated model. The fundamental difference between these three models is based upon where the intelligence is located, in the data center for the centralized model, at the network edge for the distributed model and at both for the federated model.
The IoT architecture therefore supports the client-server design and the peer-to-peer design simultaneously, which greatly enhances its capabilities.
In classic Machine-to-Machine (M2M) networks, all of the data is sent to the center of the network in the data center. However, in the IoT network, some data goes to the center and resides at the edge. The edge data may or may not go to the center of the network. There may never be any need for it to go to the center. Yet, some edge data like meter reads for billing will most certainly journey to the data center.
Some of the edge data is not actually gathered from devices, such as smart meters, but is derived and provided from device to device just when it is necessary in an “on-demand” approach. This may be smart grid data from a device that is informing nearby associated devices of its status. An example might be a recloser indicating if it is open or closed to the next recloser on the feeder.
Some edge data may only traverse the network as far as the local substation and communicate with a substation controller managing voltage or other parameters on a feeder or group of associated feeders from the same or neighbouring substations. The controller may then aggregate data for forwarding or derive new data that is forwarded to the master controller which is centrally located at the data center.
Therefore, the architecture of the network plays a key role in meeting the needs of the applications that operate over it. The architecture maps to the applications and is configured to operate in a local, regional, or network-wide level.
Figure 2 – Star Network
Figure 3 – Mesh Network
Figure 4 – Cluster Tree Network
The Internet of Things (IoT) is capable of supporting three network topologies in the wireless format. These topologies are: star, mesh, and cluster tree.
All three offer advantages and disadvantages compared to each other. For example:
Node and Connections
As with all networks, the IoT networks are composed of nodes and connections. The nodes are the devices which transmit or receive the datagrams. The connections are the means for joining the nodes into a holistic network fabric.
There are different kinds of nodes that perform different work within the smart grid network. Many are metering devices that simply provide power consumption data to some prescribed interval, often at the top of each hour for 24 reads per day, but it can be as granular as every 5 minutes for 288 reads per day. There are different types of meters and we are beginning to see an emergence of meters that provide power quality readings. These meters continuously measure and monitor frequency, voltage variation, dips and swells, voltage outages, voltage unbalance, total harmonic distortion (THD) and power factor. Therefore, the data payload per transmission is much greater than the initial consumption meters or time-of-use meters. Other devices provide alarms and status monitoring conditions. These can be from reclosers, segmentation switches, tie switches and other similar devices. Smart grid devices like cap banks, power line monitors and transformer monitors all exchange data too.
The connections are normally wireless connections, but some wired connections can also be a part of the IoT model. Wireless uses different frequency bands in different countries. In North America, the 902-928 MHz band is common for electrical solutions. In Europe the new 860-867 MHz is considered the ideal spectrum for smart grid use. Some European companies are using the 1 MHz channel at 868 MHz too. In some South America countries, the same 902-928 MHz band as in North America, but with full band power level and time duration restrictions and partial band exclusions for a middle block reserved for other purposes. In Japan, the 920-928 MHz band and the 950-958 MHz band is used, while in China, the 470-510 MHz band and the 779-787 MHz band are popular. Korea used the 917-923.5 MHz band. Worldwide the 2400-2483.5 MHz band is used too. Other bands are used in various countries that may require special approvals, but these are the most popular blocks of spectrum available for mass deployments.
The Wi-SUN physical layer supports multiple data rates in bands ranging from 169 MHz to 2450 MHz. The Wi-SUN networks make use of three main node types, but depending upon the network topology, vendor, country and other parameters, the names vary as follows:
- Nodes Types and Functions
- PAN Coordinator / Take-out Point / Gateway / Hub
- Full Function Device / Router Node / Repeater
- Reduced Function Device / End Nodes
- Connection Types
- Star – point to multipoint
- Mesh – multipoint to multipoint
- Cluster Tree – hybrid of star and mesh topologies
The longest edge is the inter-node hop with the greatest distance within a network fabric and is often the limiting factor for the data rate and the latency metrics.
Applications will be sensitive to the network topology and the associated performance characteristics for each design. Wherever possible, the applications should have priority over the network design, meaning the network is there to support the application so it should be transparent to the application and not adversely affect the performance of the application.
Some applications will not work well on these Wi-SUN networks while other applications will be ideally suited to them. The major challenge of these networks is data rate and latency. If the application can function within these limitations for data rate and latency, then all is well. However, once the application demands greater performance than the underlying network can provide, then problems start. Traffic collisions, corrupted packets, delayed packets, out of order packets and missing packets all contribute to poor or unacceptable network performance. Some of the newer federated applications that use the IEC 61850 design will not work well on these networks. For example, emerging Distribution Voltage Optimization (DVO) solutions will be challenged to function over these networks due to their demand for ultra low latency and data flows that exceed these network’s capabilities to provide. However, less demanding applications such as a centralized SCADA solution can work well. Smart metering is ideal for these networks too.
Selecting the right network architecture with the right topology will drive device interconnectivity for years to come. By connecting devices, more information is available to drive better and faster decision-making which ultimately results in satisfied customers due to high performance distribution networks.
Michael Martin has more than 35 years of experience in broadband networks, optical fibre, wireless and digital communications technologies. He is a Senior Executive Consultant with IBM’s Global Center of Excellence for Energy and Utilities. He was previously a founding partner and President of MICAN Communications and earlier was President of Comlink Systems Limited and Ensat Broadcast Services, Inc., both divisions of Cygnal Technologies Corporation. He holds three Masters level degrees, in business (MBA), communication (MA), and education (MEd). As well, he has diplomas and certifications in business, computer programming, internetworking, project management, media, photography, and communication technology.