Electric utilities have long sought to find ways to reduce costs associated with meter data collection. In the early 1980s, hand-held meter reading devices were deployed to replace manual recording of meter information. Like UPC bar codes and scanners, hand-held meter readers reduced the recording time and more importantly, reduced transcription errors. Ten years later, wireless transceivers were being fitted into meters and fixed wireless infrastructure was built to allow metering data to be brought directly into billing systems thus eliminating the need for manual or drive-by meter scanning. For utilities that serve areas with high consumer densities, costs are easily justified to install fixed wireless AMR technologies. Utilities such as rural electric cooperatives may have very low consumer densities and cannot justify the deployment of wireless AMR communications equipment to adequately cover their service territories. Fortunately, there are AMR technologies more suited to the rural utility.

PSTN or POTS, which stands for ”Public Switched Telephone Network” or ”Plain Old Telephone System,” still represents one of the lowest cost methods of carrying meter data in rural areas. Modems are installed into meters and share the consumers’ telephone lines. These devices are configured to dial out at a certain time of day, establish contact with the meter data collection computer and transfer their readings. While in contact with the host computer, the meter devices may receive new instructions such as a change in reporting schedule. This technology takes advantage of an existing communications infrastructure so there is no cost associated with having to build and maintain a dedicated network. The main disadvantage is that the telephone service may not be located close to the electrical service so that a phone line would have to be trenched in or a short-haul wireless link would need to be deployed. The system may be inconvenient for the consumer, as it must tie up the consumer’s phone line while communicating to the host computer. With a phone connection, the meter is now connected to both the electrical and telephone systems which may have grounding issues that can cause failures due to lightning-initiated surges. When choosing a telephone-based AMR system, be sure to ask if the product uses isolation relays to minimize the connection time between the phone and power systems. Telephone-based AMR systems are particularly good for those consumers who cannot be reached with other technologies. They also quickly report power outages as long as there is phone service.
Power Line Carrier (PLC) is the most practical communications technology for serving areas with low consumer density. PLC takes advantage of the utility’s existing power lines to transmit and receive data, eliminating communications wiring or wireless infrastructure. PLC has been used since the 1930s (called Ripple Signal Carrier) for load control and switching. Modern PLC differs in several important ways: it’s faster, supports two-way communications and it’s more reliable. The old ripple systems could transmit only a few bits per second. Some forms of PLC were even slower and only transmit a few bits per hour!
PLC signaling technologies can be grouped into two categories: low bandwidth and high bandwidth. High bandwidth is in the realm of Access BPL and today is used to provide broadband Internet access at frequencies between 2 MHz and 80 MHz. At these frequencies the signal is subject to significant attenuation and multi-path distortion, requiring a large investment in signal repeaters and conditioning equipment which make it economically impractical for areas with low consumer densities.

Access BPL has other technical hurdles which must be overcome before it may be widely deployed. One of the most significant of these is interference with other users of the frequencies employed by the technology. As BPL signals are injected into power lines, they tend to radiate away from those lines as a radio signal that has the potential of interfering with licensed users of the same spectrum. This interference may disrupt critical communications needed by government, military, business and volunteer users of various radio technologies. Access BPL continues to be very appealing to utilities as it promises to offer Broadband services, AMR and operational communications over the company’s power lines.
PLC frequencies up to 500 KHz are considered low bandwidth and are the most practical for rural AMR applications. This spectrum is further categorized as 0–3 KHz, 3–9 KHz, 9–95 KHz (“A” band), 95–125 KHz (“B” band), 125–140 KHz (“C” band) and 140 –148.5 KHz (“D” band). Most PLC-based AMR communications fall in between 0 Hz and A band as this frequency range represents the best tradeoff between bandwidth and signal propagation for utility distribution networks. The higher B, C and D bands are used for low voltage, shortrange applications such as X10 home automation and industrial automation communications such as CEBus and LonWorks.
In North America, distribution power lines are designed to transmit power at 60 Hz and present low impedance up to around 400 Hz. Frequencies higher than 400 Hz will be attenuated at a much greater degree resulting in reduced coverage. To compensate, repeaters and capacitor blocking units are used to extend the signal. PLC modulation techniques that keep below 400 Hz or inject at zero crossing will propagate the furthest. However, at this low frequency, very little bandwidth is available for transmitting and receiving data. Repeaters do provide the ability to pass signals to very hard-toreach locations and can be used to pass the PLC signal around normally open feeder switches eliminating the need for additional substation PLC communications equipment.
Data rates of about 15 bits per second can be reasonably expected for 60 Hz-based modulation techniques. PLC modulation in the A band can produce data rates of about 75 or greater bits per second. By injecting the PLC signal on each phase the overall speed can be improved by reading each phase in parallel (this will not improve out-of-cycle, individual read times, however). A side benefit of reading individual phases makes it possible to determine which phase a particular meter is on.
The PLC signal can be coupled to the power system either by transformers or capacitors. Transformers installed at a substation can be more costly to purchase, install and maintain. Consider also the cost of substation PLC signal injection and receiving equipment. Some equipment is temperature sensitive and requires installation into climate-controlled substation buildings. The annual cost to operate this equipment may also be significant as power requirements vary substantially between PLC vendors’ equipment. PLC provides a communications path from the meter to the substation. A different communications media is required to get the data from the substation to the host computer. The substation PLC equipment should be able to support a variety of communications paths, including PSTN, wireless, broadband and satellite. It should also have ample intelligence and local memory to operate independently of the host computer should the host to substation communications be interrupted.
The devices installed into billing meters for two-way communications are called transceivers or transponders. These devices can retrofit existing electro-mechanical meters or electronic meters. Transceivers installed into electro-mechanical meters must measure disk rotation to determine energy and demand. Transceivers in electronic meters read the meter’s energy registers directly. The indirect method of reading electromechanical meters can lead to discrepancies between the transceiver and meter dials. Is it better to retrofit existing electro-mechanical meters or purchase new electronic meters with AMR transceivers already installed? The AMR transceivers cost around $50 to $80 depending on features and options. A new electronic meter will cost another $35 to $40. Once the labor cost to retrofit and test an existing meter is added there is little difference in cost. Solid-state meters offer much higher accuracy, don’t need periodic recalibration and provide the convenience of direct reading for consumers (no billing multipliers are needed to determine actual energy usage).
Three-phase meter reading for commercial and industrial accounts have additional requirements such as demand and time-of-use billing parameters. Modern electronic three-phase meters also provide a vast amount of non-billing data such as voltage, current and power quality. Many of these devices have their own communications interfaces such as RS-232, telephone modem, and Ethernet. AMR transceivers must be able to handle, at a minimum, the demand and time-of-use registers. Because there is no standard interface for adding internal AMR transceivers to various vendors’ three-phase meters, a separate internal interface card has to be developed for each type of meter. Alternatively, an external AMR transceiver can be used to connect to the meter’s serial port or KYZ outputs. The advantage of an external interface is that only one type needs to be stocked to interface with many different types of meters. Other features such as I/O can be added to remotely monitor and control loads.
The cost of PLC-based AMR deployment has declined significantly in the past five years. It is however, still hard to justify deployment to rural areas based only on the benefits of automating meter reads. Having two-way communications coverage of the utility’s entire distribution system opens up possibilities for many operational efficiencies. Some AMR meter transceiver manufacturers have incorporated several features that can help reduce losses and improve system reliability and consumer satisfaction. Service voltage can be monitored and even recorded with time and date stamps, which are used to indicate tampering, over- or under-voltage conditions, and to verify that a consumer’s service is present. Demand can also be determined and profiles logged that can be used to resolve high bill complaints and calculate coincidental peaks and diversity factors to aid in system planning.
Other devices can be monitored and controlled using two-way PLC communications. Remote disconnect collars can be added between the meter and base allowing the utility to remotely disconnect and reconnect or even current limit a service. Load control receivers can be added to control air conditioning and hot water tanks using sophisticated algorithms that minimize discomfort and optimize peak reduction. Industrial and agricultural loads such as oil pump jacks and irrigation pivots can also be controlled to reduce peaks. Capacitors, voltage regulators and even polemounted reclosers can be monitored and controlled providing a comprehensive distribution monitoring and control system.
Two-way, real-time communications also makes it possible to support interval metering. Instead of collecting monthly readings, interval metering requires energy to be recorded on intervals of typically fifteen minutes. This matches the demand interval for most wholesale markets and allows the retail consumer to participate indirectly through demand response programs. Although not widely implemented today, FERC is actively promoting demand response as a viable method of demand reduction.
Two-way PLC communications technologies provide more benefits when operational elements are added. However, as more operational information is generated, higher bandwidth is needed to prevent congestion. The higher the PLC communications data rate the more useful it is for collecting operational and billing data and sending control signals.
An often overlooked but very critical aspect of an AMR system is the meter data collection software or host system. Since information stored in the meter data collection software will be shared by nearly every group within a company, it must have the appropriate functionality, utility, expandability, scalability, supportability and ability to be integrated with other applications.
Basic functionality should include a relational database for storing meter and operational data from one of the major database vendors to ensure reliability, performance and interoperability. A meter data collection system built on a three-tier architecture model such as Microsoft’s .NET architecture separates the user interface from the business logic and Database Management System (DBMS) access layer. This architecture takes advantage of web browsers to provide simple and user-friendly application interfaces that can be used from any desktop computer. It’s also easier to maintain and support as the business logic need only be changed in one location instead of every desktop. Databases can also be added or changed without affecting the desktop clients.
The software should be modular so that it can be ordered with only the functionality needed but can be easily expanded later. For example, AMR data collection would be included in the base platform and load control or capacitor control could be added later. The base software should also include configuration screens, alarming and basic reporting. Most PLC AMR systems rely on the host computer to poll the substation communications equipment, which in turn polls the remote transceivers. In the event of a power outage, the affected transceivers will not be able to respond, as they no longer have power. The host computer should detect this condition and report it as an outage. Preconfigured demand and energy reports should also be included along with a simple-to-use report builder. The host computer software should be able to detect when feeders have been re-configured so that services that were fed from one substation are now being fed from another substation.
The host software should provide pre-built interfaces to most popular Consumer Information Systems or billing systems and support standards such as MultiSpeak, XML and ODBC to ease integration with other applications such as Outage Management, GIS and SCADA. Another important feature is a scripting language that can be used to extend functionality and create robust connections with other applications. The scripting language should support constructs to handle exceptions caused by unexpected errors. For example a script could be written to move meter data to a remote billing system but be able to handle errors returned from the interface without stopping.
Two-way PLC AMR systems can be justified by the rural utility if the communications backbone can be leveraged through additional operational functionality. Communications bandwidth is the critical limiting factor for retrieving increased volumes of meter and operational data at near real-time speeds. Therefore, PLC technologies that provide higher bandwidth will deliver more combined value today and in the future. Host software is critical to the operation of an advanced AMR system and must receive the same or more scrutiny during the evaluation and implementation process.