AMI Communications Technology
Advanced metering infrastructure (AMI) communications is a central topic for AMI and smart grid technology evaluations throughout North American utilities.
By Jim Roche, Cooper Power Systems/Cannon
Advanced metering infrastructure (AMI) communications is a central topic for AMI and smart grid technology evaluations throughout North American utilities. The technologies presented within this article are indicative of the industry, but this list is not exhaustive.
Automated meter reading (AMR) technology dawned primarily between the mid-'80s and early 1990s. In the beginning, there were three primary options:
- (1) walk-by/drive-by solutions,
(2) one-way, inbound systems, and
(3) two-way, dial-up, phone-based solutions.
Walk-by/drive-by solutions are used still for AMR data collection where radio frequency (RF) modules chirp their readings periodically and a device, either handheld or a mobile fleet-mounted receiving unit, picks up the data when nearby.
One-way, inbound systems involved programming meters to send in readings at periodic rates–typically daily–sometimes called bubble-up networks. These used consumer phone lines, radio technology or one-way, legacy power line carrier (PLC) signals transmitted over the utility's distribution lines.
Dial-up phone systems are straightforward and use a computer to dial modems attached to electric meters, particularly at commercial accounts. A few of these solutions have evolved, allowing adequate data transfer with modern telephony technology, predominantly still used for small batches of meters rather than entire service territories.
These days AMI communications typically break into one of three main subsystems: wide area networks (WAN), local area networks (LAN), and the newest, home area networks (HAN), though these terms are not used universally. WAN communications refers to backhaul communications media that connect to the LAN. One can think of the WAN as an interstate highway: plenty of room for lots of traffic (bandwidth), and it links to cities (or gateways) where it connects to smaller thoroughfares (or LANs), such as state highways. The LAN, akin to the state highway network, handles the bulk of day-to-day regional traffic (or AMI messages) and ties to a single street entering a cul-de-sac. The street that connects to this small neighborhood represents the emerging concept of a HAN, which would serve only one home–a concept to revisit later.
People often call this interstate highway the bulk communications channel as it passes large payloads of data between LAN gateways and the master station usually located in a utility's office. Media used for WAN communications typically use longer-range, high-power radios or Ethernet IP-based solutions. Common options include microwave and 900 MHz radio solutions, as well as T1 lines, digital subscriber lines (DSL), broadband connections, fiber networks, Ethernet radio, digital cellular and WiMAX.
The LAN is the core of AMI communications technologies and typically differentiates vendors. This subsystem provides two-way communication paths directly to the utility's meters or AMI endpoints. The two predominant technologies involved are, as they were in the beginning, PLC and RF. Because they are two-way networks with significant speed and bandwidth, however, they differ substantially from the legacy technology mentioned previously.
RF AMI Networks
RF solutions include technologies that use an assortment of frequencies, cover a range of distances and implement a variety of network topologies or methodologies. The two primary RF AMI network topologies include star networks, sometimes called point-to-multipoint systems, and mesh networks.
Bandwidth, or data capacity, of a radio system typically is inversely proportional to the distance the communication message can cover. Thus, designing communication systems typically involves selecting an optimum balance of distance and speed or bandwidth, which are interdependent on transmit power and frequency, as well as the cost of the transmitter. Typical frequencies include 900 MHz and 2.4 GHz, although others exist.
As suggested, these radio systems can be used in two configurations. Star or point-to-multipoint typically involves a central gateway to a number of AMI endpoints (meters). This gateway could be a communications tower with a transmitter or a centrally located meter that talks to child or slave meters. For example, Gateway A may talk to meters 1, 2, 3 and 4. While redundant paths may exist to these slave meters, the relationships are typically pre-set and consistent.
A mesh system allows communication paths to weave together, often in a daisy-chain pattern. In this example, Gateway A may talk to meters 1 and 2, with meter 2 talking to meter 3, and meter 3 communicating with meter 4 to complete the link.
Pros and cons can be investigated elsewhere. Typically, RF solutions are most cost-effective for urban, densely populated service areas.
PLC AMI Networks
Again, PLC communications involve transmitting and receiving messages via a utility's distribution power lines that are already connected to every meter. The PLC systems available use frequencies and modulation techniques that again translate into a range of available speed and bandwidth options. These include using the 60 Hz power wave, as well as superimposing high-bandwidth carrier signals of other frequencies onto the power line.
PLC signals most commonly are coupled onto a utility's power lines at its distribution substations, where WAN backhaul communications equipment and LAN AMI injection equipment can be colocated to minimize expenses.
PLC solutions are cost-effective particularly in low-density areas such as rural and suburban service territories where feeders serving meters tend to be lengthy. North American PLC signals are routinely used to communicate with AMI endpoints that might be 10 to 100 miles from a substation.
Hybrid AMI Networks
As larger utilities serve diverse territories, including high- and low-density areas, hybrid solutions often are considered to meet utilities' needs. This is often a combination of RF and PLC systems, which may or may not be tied together into one head-end master station.
Additional Uses of LAN AMI Networks
LAN communications modules also can be used in devices other than meters to facilitate communications, maximizing a utility's return on its AMI investment. These include demand response (DR) devices, also called load management or load-control devices, and distribution automation (DA) equipment including smart sensor products.
While AMI LAN modules can be used for DR, non-AMI communications options exist, and sometimes non-AMI options are more cost-effective or offer minimal latency. This may be the case if the system was optimized such that all messages have equal priority or network latency was built in to accommodate meshing capabilities or system redundancies. If planning to use an AMI LAN to facilitate DR programs, a utility must analyze the system characteristics and vendors' DR experience.
DA is an ever-expanding suite of solutions, including tools providing monitoring and control capabilities for capacitor banks, voltage regulators, reclosers and sectionalizing equipment, intelligent electronic devices (IEDs) and sensors detecting everything from faulted circuits to energy theft. These solutions allow utilities to maximize system performance and efficiency, thus this area of automation fits into the smart grid concept. Again, some AMI networks lend themselves to facilitate real-time control messaging while others do not.
HAN was coined in the past few years and refers to communication to devices behind a meter inside a consumer's home. This includes messages to present information via in-home displays (IHDs), as well as messages DR devices can use to control key appliances to manage energy usage and capacity constraints. This network is being conceptualized in response to mandates across the nation to improve energy efficiency and educate and empower electrical consumers.
ZigBee is a common buzzword surrounding HAN communication conversations. Often confused for a communication technology, it's a network messaging protocol. ZigBee messages are transported via other RF messaging protocols in unlicensed RF spectrum shared by Bluetooth and Wi-Fi to communicate throughout a home.
A few RF and PLC communications technologies exist in this evolving arena. In this scenario, a meter would contain transmitters to communicate to the LAN and devices on the HAN, linking a utility to its customers by leveraging its AMI investment. Most HAN traffic is likely to be between only the meter and the IHD, displaying the meter's usage or demand information.
Summary and Observations
Three primary subsystems make up the AMI communications network: the WAN, LAN and HAN (see figure). Technology options exist for each subsystem, optimized with tradeoffs to balance speed, bandwidth and distance, as well as cost. RF systems use either a mesh network or a star network topology. RF solutions typically are best-suited for high-density, urban areas, whereas PLC solutions are well-suited for lower-density coverage of suburban and rural territories. The HAN will develop and evolve in coming years.
Effective AMI solutions will allow substantial information sharing among other utility software systems; system-generated reports to be delivered to stakeholders; automated notifications to alert service and operations personnel; coordination with power suppliers and regulatory bodies; information exchange with consumer base, etc.
Communications technologies will evolve, and these networks lend themselves to evolution, so investments made with appropriate due diligence should fare well.
Jim Roche is senior marketing manager for AMI solutions for Cooper Power Systems/Cannon. E-mail him at firstname.lastname@example.org.