{\rtf1\ansi\ansicpg1252\uc1 \deff0\deflang1033\deflangfe1033{\fonttbl{\f0\froman\fcharset0\fprq2{\*\panose 02020603050405020304}Times New Roman;}{\f2\fmodern\fcharset0\fprq1{\*\panose 02070309020205020404}Courier New;} {\f642\froman\fcharset238\fprq2 Times New Roman CE;}{\f643\froman\fcharset204\fprq2 Times New Roman Cyr;}{\f645\froman\fcharset161\fprq2 Times New Roman Greek;}{\f646\froman\fcharset162\fprq2 Times New Roman Tur;} {\f647\froman\fcharset186\fprq2 Times New Roman Baltic;}{\f654\fmodern\fcharset238\fprq1 Courier New CE;}{\f655\fmodern\fcharset204\fprq1 Courier New Cyr;}{\f657\fmodern\fcharset161\fprq1 Courier New Greek;} {\f658\fmodern\fcharset162\fprq1 Courier New Tur;}{\f659\fmodern\fcharset186\fprq1 Courier New Baltic;}}{\colortbl;\red0\green0\blue0;\red0\green0\blue255;\red0\green255\blue255;\red0\green255\blue0;\red255\green0\blue255;\red255\green0\blue0; \red255\green255\blue0;\red255\green255\blue255;\red0\green0\blue128;\red0\green128\blue128;\red0\green128\blue0;\red128\green0\blue128;\red128\green0\blue0;\red128\green128\blue0;\red128\green128\blue128;\red192\green192\blue192;}{\stylesheet{ \widctlpar\adjustright \cgrid \snext0 Normal;}{\*\cs10 \additive Default Paragraph Font;}{\s15\widctlpar\adjustright \f2\fs20\cgrid \sbasedon0 \snext15 Plain Text;}{\s16\widctlpar\tqc\tx4320\tqr\tx8640\adjustright \cgrid \sbasedon0 \snext16 header;}{ \s17\widctlpar\tqc\tx4320\tqr\tx8640\adjustright \cgrid \sbasedon0 \snext17 footer;}{\*\cs18 \additive \sbasedon10 page number;}}{\info{\title Practical problems of using the distribution lines for Automatic Meter Reading}{\author Mitchell D. Smith} {\operator S\'f8ren Hess}{\creatim\yr1999\mo9\dy27\hr13\min30}{\revtim\yr1999\mo9\dy27\hr13\min30}{\printim\yr1999\mo9\dy14\hr11\min42}{\version2}{\edmins0}{\nofpages9}{\nofwords3205}{\nofchars18271}{\*\company BCN Data Systems, LLC}{\nofcharsws22438} {\vern113}}\margl1319\margr1319 \widowctrl\ftnbj\aenddoc\lytprtmet\hyphcaps0\formshade\viewkind1\viewscale75\pgbrdrhead\pgbrdrfoot \fet0\sectd \linex0\headery709\footery709\colsx709\endnhere\sectdefaultcl {\footer \pard\plain \s17\qc\widctlpar \tqc\tx4320\tqr\tx8640\adjustright \cgrid {Page }{\field{\*\fldinst {\cs18 PAGE }}{\fldrslt {\cs18\lang1024 1}}}{ \par }}{\*\pnseclvl1\pnucrm\pnstart1\pnindent720\pnhang{\pntxta .}}{\*\pnseclvl2\pnucltr\pnstart1\pnindent720\pnhang{\pntxta .}}{\*\pnseclvl3\pndec\pnstart1\pnindent720\pnhang{\pntxta .}}{\*\pnseclvl4\pnlcltr\pnstart1\pnindent720\pnhang{\pntxta )}} {\*\pnseclvl5\pndec\pnstart1\pnindent720\pnhang{\pntxtb (}{\pntxta )}}{\*\pnseclvl6\pnlcltr\pnstart1\pnindent720\pnhang{\pntxtb (}{\pntxta )}}{\*\pnseclvl7\pnlcrm\pnstart1\pnindent720\pnhang{\pntxtb (}{\pntxta )}}{\*\pnseclvl8 \pnlcltr\pnstart1\pnindent720\pnhang{\pntxtb (}{\pntxta )}}{\*\pnseclvl9\pnlcrm\pnstart1\pnindent720\pnhang{\pntxtb (}{\pntxta )}}\pard\plain \s15\widctlpar\adjustright \f2\fs20\cgrid {\b\fs24 Practical problems of using the distribution lines for Automatic Meter Reading \par }\pard \s15\widctlpar\adjustright {\b\fs24 \par \par \par Author: \tab F. M Gray\tab \tab \tab \tab \tab Date: 7th September 1999 \par \tab \tab UK Consultant \par }{\b \par }{\b\fs24 \par \par }{\b \par }{\b\fs24 Executive Summary \par }{ \par }\pard \s15\widctlpar\adjustright {The Medium and Low voltage electricity distribution network is increasingly used, or proposed for use, as a communication medium for Home Automation and Fixed Network Remote Meter Reading (NMR). Such systems are variously referred to as Power Line Carrier (PLC), Distribution Line Carrier (DLC) or mains signaling. \par \par These methods of communication usually involve the superimposition of a high frequency carrier, in the range 9 kHz up to 20 MHz, on to the power line. \par \par Alternative types of PLC systems use either very low frequency carriers, less than 1 kHz, or distort the waveform to transmi t data. This type of communication can only support low data rates or require a significant level of power to inject a signal (which translates into an expensive transmitter requirement relative to radio transmitters communicating the same data). These systems are therefore limited in application or are an uneconomic solution for the communication of data up from a meter (as opposed to down to the meter). As a result, the focus of this paper is on PLC systems that use a high frequency carrier to transm it data ("HFPLC") because they can offer higher data rates and therefore greater functionality. \par \par In spite of the apparent attractiveness of the technique, there are many practical difficulties in using the electricity distribution network as a communication medium. The potential for spurious emissions, from high frequency carrier signals, to cause i nterference to existing radio services is of growing concern. The problem is particularly acute when the distribution network is used as a local area network to communicate to a remote point outside the bounds of a consumer's own building. \par \par The nature and characteristics of distribution networks makes the prevention of spurious emissions from HFPLC extremely difficult, and possibly uneconomic to deal with. \par \par The purpose of this paper is to highlight the author's concern that any proliferation of HFPLC would pose a serious threat to the radio environment. \par The threat is particularly real from those systems that use increasingly high carrier frequencies. \par \par To present a balanced view, the problems of realizing a practical means of communication, via the distribution network, are discussed with particular reference to those effects that impact on radio services. \par \par \par \par \par The author reaches the conclusion that the threat to radio services from high frequency PLC, and the difficulty of keeping spurious emissions within reasonable bounds, justifies the promotion of alternative media for remote meter reading and other endpoin t monitoring applications. \par \par Low Power Radio (LPR) is n ow a viable alternative to PLC for Automatic Meter Reading technologies ("AMR" or "Monthly" technologies) and full-scale, real-time NMR systems. In fact, there are now large-scale, radio-based NMR systems operating in the U.S. for the benefit of electric and gas utilities. Unfortunately, at the moment, there is no exclusive radio band within the EU adequate for Network Meter Reading. \par \par The allocation of a dedicated radio frequency band for Automatic and Network Meter Reading would seem to be the optimum way forward and, at the same time, remove the threat to the radio environment from high frequency PLC. \par \page }{\b\fs24 Background \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright {The increasing interest in, and use of, electricity distribution networks as a means of communication is driven by three factors: \par \par \'b7\tab Home Automation and the growing interest in remotely controlling and monitoring domestic appliances. \par \par \'b7\tab Competition and deregulation of the electricity supply Utilities and the need for more metering information to differentiate services. \par \par \'b7\tab The need to be more cost competitive in the operation of distribution networks and the supply of energy services. \par \par }\pard \s15\widctlpar\adjustright {This paper focuses on the impact of utilities using the power distribution network as a local area network (LAN). \par }\pard \s15\widctlpar\adjustright { \par As time goes by, Utilities will place increasing demands on communication links, in order to retrieve data on the consumption patterns of their consumers. Historically, direct communication with electricity meters has been confined to high volume account s, most usually via telephone modems. Communication with domestic meters has been impractical and uneconomic, and therefore tends to be done manually and infrequently. \par \par With increased competition, and the falling cost of electronics, Utilities are racing to add value to their businesses and entice consumers with new services. Squeezing more from their existing assets and adding a communications capability is often seen as the key to future growth. At least one Utility has proposed using the low voltage distribution network as a communications vehicle to offer telephone and Internet services. \par \par There is little doubt that electricity Utilities will play an important part in the future development of the information super-highway. These companies will be both major providers and users of Internet technology. They are bound to conduct experiments to see how much can be achieved with PLC, without undue cost or impairment of other services, particularly those dependent on radio transmissions. \par \par Network Meter Reading (NMR) is seen to be fundamental to enabling many of the future services a Utility may wish to offer, regardless of the communications medium. In the broadest terms, NMR is the }{\i remote}{ and }{\i frequent}{ collection of consumption data from customers' utility meters. Many different media have been proposed, including telephony, radio, power line carrier and satellite communications technologies. NMR can provide water, gas and electric utility-service com panies with the opportunity to increase operational efficiency, improve customer service, reduce data-collection costs and gain more detailed information on their customers' usage patterns. All of these benefits are made possible by low-cost, daily or more frequent metering of customer energy usage information, which can be provided by NMR systems; therefore NMR is not the simple automation of a meter read using a drive-by or handheld device, more commonly referred to as AMR technologies. \par \par NMR also provides the customer with significant benefits, by providing increased meter-reading accuracy, fewer estimated bills, rapid response to read requests, reduction of loss by means of tamper detection and increased benefits from competition. \par \par Detailed usage information about individual sites enables the Utility to offer variable rates and encourage price-responsive behaviour among customers. \par \par \par }{\b\fs24 Utilities and Power Line Carrier \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright {Any communications network considered by electric Utilities must cover broad geographic areas and a large population. A single communication medium is unlikely to reach the entire pop ulation so multiple technologies may need to be exploited. \par \par For over 25 years, PLC has remained the electricity companies' greatest hope for data communications. The main attraction has been that existing cabling could potentially be used without the need for any new connections. All meters and appliances involv ed in such a system are already connected by the main power cabling and installation is potentially simple. In addition, usually the distribution network belongs to the Utility company and therefore, in theory, PLC is under their total control. \par \par PLC has been extensively applied for meter reading and related applications in the USA and Italy and in many other parts of the world it has been the subject of extensive trials. For instance, in Japan alone, PLC technologies have been under investigatio n for 30 years. In Australia, utilities have used a form of PLC (for the narrow purpose of a broadcast load-switching application) that was developed in Switzerland some 30 years ago. Numerous other systems have been developed and tested. \par \par 'Ripple' Control Systems, such as the PLC technologies used in Australia, are extensively used to transmit control data over the Medium and High voltage networks. The signaling frequency, however, is low and the data rate is slow (10's bits per second). Although effective for load control purposes, there is limited scope for future expansion, and most existing deployments around the world were never intended to transmit meter reading data from the consumer to the utility. \par \par After the expenditure of so much effort, and with so many apparent benefits, one might ask why it is that PLC has not become the dominant method of reading meters. In the next section, an attempt is made to answer this question and to make the case for t he adoption of a radio solution. \par \par \par }{\b\fs24 Architecture of a Distribution Network \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright {A fundamental limitation of PLC is that the distribution network does not provide a direct link between the meter and the utility billing computer. \par \par Electricity distribution n etworks are composed of a number of levels. Each level has a progressively reduced operating voltage down to the level supplied to the domestic consumer. This is a necessary requirement for the efficient transmission of electricity over long distances. \par \par The first level, where PLC is typically applied, is the 11,000 kV medium voltage (MV) network. The MV network distributes power directly to larger commercial/industrial users, and to domestic and small commercial consumers via a large number of distribu tion transformers. \par \par It is in these distribution transformers that the voltage is transformed from three phase 11kV to three phase 415V. The 415V network is very extensive, is known as the Low Voltage (LV) network and supplies 230V single phase to domestic consumers. \par \par Distribution transformers may be rated at between 200 and 1,000kVA and each supply up to 200 domestic consumers. \par \par It will be obvious that distribution networks and transformers are designed to transmit 50/60 Hz voltage and current with as li ttle loss as possible. Power Factor correction capacitors are often fitted in the switch rooms of industrial premises and are also inherent within certain loads such as fluorescent light fittings. \par \par MV and LV distribution networks will incorporate a mixture of underground and overhead cables and may run for distances of several kilometres. \par \par Networks are configured so that routes may be switched to permit sections to be isolated in the event of a fault \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright { \par }{\b\fs24 Power Line Carrier and Standards \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright {PLC of one type or another has been in use for very many years. Carrier frequencies range from as low as 110Hz ('Ripple' control) to as high as 148,5 kHz for Home Automation. \par \par Standards have evolved to permit the distribution network to be used for different applications. These standards have been derived by expert committees reporting to IEC (and CENELEC). New emerging systems are now proposed that will operate at significan tly higher frequencies ranging from 1 MHz to 20 MHz. There are no defined standards for operation at these frequencies. \par \par European Standard EN50065-1 has been in existence since 1990 and covers the frequency range of 3 kHz to 148.5 kHz. The Standard segments the available frequency range according to application. \par \par Three generic bands A, B and C are defined. \par \par Band A (3 - 95 kHz) is defined for utility applications \par Bands B and C (95 to 148,5 kHz) for Home Automation \par \par In addition to frequency segmentation, the Standard defines maximum voltage levels and total harmonic distortion (THD) limits at the point of signal injection. \par \par Signal levels are limited to a few volts at the injection point with a total harmonic distortion (THD) better than 1%. \par \par \par }{\b\fs24 Limitations of Power Line Carrier \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright {For application to NMR, the primary function of PLC would be to transfer metering data, via the low voltage distribution network, back to a local data concentrator at the distribution sub-station. \par \par The use, and limitations, of PLC as a local area network, (particularly with respect to the communication of data beyond the confines of a building) are discussed in the next section. \par \par \par }{\b\fs24 Spurious Radio Frequency Emissions \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright {The major problem with high frequency PLC ("HFPLC") is its potential to cause spurious emissions of radio frequency energy. \par \par Spurious emissions can be both at the carrier frequency and at harmonics thereof. Distribution cables, particularly if overhead, will radiate directly as antennae and/or act as leaky feeders. \par \par Many current PLC systems use narrow band carriers to transfer the digital data. Large currents will be injected at the carrier frequency. These might be at the same frequency as low frequency services such as Rugby (60 kHz) and European Time standards (77 kHz). Even in systems that use frequency hopping or spread spectrum, the narrow band availab le can result in significant energy at a given frequency. \par \par Harmonics of the PLC carrier can extend the effect of radio frequency emissions still further to affect long, medium and short wave services. With the proposed introduction of higher frequency carr iers (1-20 MHz), there is the potential for harmonics to extend to VHF. \par \par Although EN50065 defines the level of harmonics at the point of injection, there is no control on the voltage multiplying effects which may be caused by non linear loads or of discontinuities within the distribution network. \par \par Semiconductors within many modern appliances will appear as non linear devices and cause the generation of harmonics of the fundamental PLC signal. Natural non-linearity, e.g. due to oxidized joints, in the di stribution network may also cause the generation of harmonics. \par \par Cable spurs will be of variable lengths and may resonate (to serve as antennae) at the carrier frequency or harmonicas thereof. \par \par There is already documented evidence of HFPLC systems radiating at levels sufficient to disrupt radio services. Inevitably the effect will become worse if higher carrier frequencies are permitted. \par \par }\pard \s15\widctlpar\adjustright {The inevitable result is that these spurious emissions will cause the disruption of a number of radio services and the pollution of a valuable part of the radio spectrum. \par }\pard \s15\widctlpar\adjustright { \par The prevention of spurious emissions from the power frequency distribution network, due to HFPLC, is not a practical proposition. \par \par The practical difficulties of propagating a PLC signal over the distribution network is discussed in the next section. Successful propagation often requires the injection of very high power with the consequence of even greater emissions. \par \par \par \par \par \par }{\b\fs24 Blocking Effect of the Distribution Transformers \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright {HFPLC carrier frequencies are signi ficantly higher than the power frequency. Distribution transformers act as low pass filters so that HFPLC propagation will be confined to a given section of the low voltage network. This means that, for each isolated section of the LV network, it is nec essary to fit a data concentrator and secondary communications path back to the control centre. \par \par This is not a problem where a large number of consumers are supplied from a given distribution transformer. It does, however, become significant in rural situations. \par \par A Utility will typically have 10,000 - 15,000 small transformers in rural areas. In these circumstances, HFPLC may be uneconomic and radio could provide a better solution. \par \par \par }{\b\fs24 Variable Signal Attenuation \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright {Power cables radiate in many directions from an electricity substation. Loads will be randomly connected and spurs taken off to other parts of the network. \par \par Cables can present a significant impedance to high frequency carriers. Applied loads may include power factor compensation capacitors with a very low resistance at high frequency. \par \par The net effect is that HFPLC signals can be very severely attenuated and often to such an extent that signals cannot be received. The degree of attenuation will be frequency dependent and variable with the connected load. \par \par Attenuation may often be most severe when the network is heavily loaded and reliable communication is critically required for load shedding. \par \par To overcome the problem of signal attenuation repeaters may be used or injected signal levels may be increased. The use of sophisticated modulation techniques may alleviate some of the difficulties but, if signals have been attenuated beyond a certain level, no amount of sophistication will be one hundred percent successful. \par \par The simplest expedient of raising signal level will also lead to increased pollution of the radio spectrum. \par \par \par }{\b\fs24 Standing Waves \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright {The HFPLC carrier wavelength may at times be comparable to the length of a cable run. Under such circumstances resonance will occur. The resulting stand ing wave can either magnify the signal at a point or result in a 'null'. A standing wave will increase radio emissions and often more power is injected to compensate for a potential lower impedance. \par \par \par \par \par \par \par }{\b\fs24 Noise \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright {Non-linear loads, switch mode power supplies, electronic lighting ballasts and arcing of switches can all result in the generation of significant 'noise' at all frequencies used for PLC. \par }\pard \s15\widctlpar\adjustright { \par The 'noise' levels combined with attenuation can rapidly cause the signal to be 'lost'. An obvious solution would be to inject a higher power level. \par \par \par }{\b\fs24 Limitations for Other Utilities \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright { In addition to supplying electricity, a number of Utilities are now providers of gas and water. Gas and water meters are often located away from the incoming electricity supply and would require extensive cabling to connect them together in order to util ize the PLC network. Whether the PLC technology is low or high frequency, this is a significant economic limitation in the ability to gain full usage of PLC communications infrastr ucture compared to using radios at each endpoint, which can operate by battery power. \par \par In addition, a great deal of potentially expensive attention would need to be paid to electrical safety issues if data from gas and water maters are to be linked into a common PLC system. \par \par \par }{\b\fs24 Conclusion \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright {The purpose of this paper has been to indicate that, although PLC may appear to be a convenient means of data communication, the limitations of the medium present serious practical difficulties. \par \par If the power distribution network is limited to the superimposition of very low frequency carriers and data rates, PLC has already been shown to be a viable communication medium from the utility to the meter. 'Ripple' control is widely installed for one-way communication for Tar iff and Load Control. The opposite direction of communication using low frequency PLC is potentially economically problematic due to the cost of a relevant PLC transmitter that would have to be installed at every meter. In addition, the low data rates i nherent in low frequency PLC technologies limits the functionality of network applications generally. \par \par In spite of the data rate benefits, problems have already been experienced when higher frequency carriers (9 kHz to 20 MHz) are used to transfer data. Signaling problems can usually be resolved but not without added cost and complexity. \par \par The spurious emission of radio frequencies is intrinsic and by far the most serious problem with HFPLC. In fact, this may be a problem that is impossible to resolve. \par \par In the author's opinion it is unreasonable to compromise valuable radio spectrum by using HFPLC technologies when there are viable alternatives for network meter reading. \par \par A practical alternative is Low Power Radio (LPR). LPR can provide a more reliable communication medium than HFPLC. All Utilities (gas, water and electricity) can safely be serviced from a common system, not to mention other monitoring and control applic ations such as home security and office machine monitoring, home management applications, etc. \par \par Radio emissions from low power radio systems are predictable and can be contained within the allocated band. \par Spurious emissions and pollution of other radio channels is not an issue with a correctly designed radio transmitter. The nature of the power distribution network means that this is a parameter that is difficult to contain with HFPLC. \par \par Radio can offer a lower cost and more flexible solution for the large scale collection of metering data than either HFPLC or low frequency PLC technolo gies. A vast number of meters (over 300 million in Europe) can be supported within a relatively small radio frequency allocation. In addition, in the U.S., radio-based NMR technologies are deployed and operating in scale today. \par \par \par }{\b\fs24 About the Author \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright {The author has over 35 years experience in the design of electronic products for the electricity supply industry. \par \par He was formerly Chief Development Engineer at GEC Meters where, amongst other things, he was responsible for the design of the Company's Radio Teleswitch and electronic energy meters. \par \par GEC was a world leader in the design of high reliability protection and metering equipment for the electricity utility industry. \par \par Whilst with GEC, he participated in a number of UK committees, one of which lay the foundations for EN50065. As a member of the British Metering association Technical Committee he was heavily involved in EMC and electrical safety issues. \par \par He was also responsible for the development of a power line control system known as CycloControl. CycloControl is still in current use for the control of street lighting and the control of Tariffs and heating loads. \par \par CycloControl has been successfully applied around the world and other companies have extended the basic concept and applied it to meter reading. Over 1,000,000 of these devices have been produced and installed. \par }\pard \s15\widctlpar\adjustright { \par }\pard \s15\widctlpar\adjustright {In addition he was responsible for the design of one of the world's first commercial industrial based HFPLC system known as 'Mains Link'. \par \par During his time with GEC Meters he presented many papers at the Institution of Electrical Engineers and elsewhere. \par \par He is a Radio Amateur with call sign G3TBH. \par \par He is now an independent consultant and until recently specialised in training engineers in design for electrical safety and EMC. He continues working in support of BLD Computer Solutions, a small company that designs and markets products using the Cyclo Control technology. \par \par \par }\pard \s15\widctlpar\adjustright { \par }}