DESIGN OF A ROBUST PREPAID ENERGY METERING AND BILLING SYSTEM. B.O. Omijeh

Transcription

1 DESIGN OF A ROBUST PREPAID ENERGY METERING AND BILLING SYSTEM B.O. Omijeh Department of Electrical/Electronic Engineering, University of Port Harcourt, Port Harcourt and G. I. Ighalo Department of Electrical/Computer Engineering, Ambrose Ali University, Ekpoma Abstract Energy meters in Nigeria have dominantly been electromechanical in nature but are gradually being replaced by more sophisticated and accurate digital and electronic meters. Errors get introduced at every stage of energy billing, like: errors with electro-mechanical meters, human errors while noting down the meter reading; and error while processing the paid bills and the due bills. There is no proper way to know the consumer's maximum demand, usage details, losses in the lines, and power theft. The remedy for this drawback is a prepaid energy billing, which could be titled, Pay before Service. There are clear results from many countries, where prepaid system has reduced the revenue loss by a large amount. A prepaid energy meter enables power utilities to collect energy bills from the consumers prior to the usage of power by delivering only as much as what has been paid for. In this work, a robust and a more efficient prepaid energy metering which uses the existing Global System for Mobile communication (GSM) networks is presented. The technique includes a GSM-Based Energy Meter(GBEM), GSM-Based Recharge Module(GBRM) where by the power utility recharges the GBRM remotedly through mobile communication based on customer s request; and GSM-Based Tamper detector(gbtd) which detects abnormalities and sends sms alert to power utility for on site visit or investigation. A prior billing is bound to do away with the problems of unpaid bills and human error in meter readings, thereby ensuring justified revenue for the utility. Keywords: SMS, GSM, microcontroller, energy meter, server Introduction In recent years, Nigerian power sector has been facing a serious problem of lean revenue collection with respect to energy supplied due to energy thefts and network losses. It is observed that one of the faulty subsystems is the metering and meter-reading system, which has to improve, if revenue collection is to be increased (Nwaoko, 2006). The traditional electro-mechanical meters still widely used today, are highly mechanical and human error bound. Collection of meter readings is also inefficient, because a meter- reader or a personnel of an electricity company has to physically be on-site to take the readings. This method of collecting reading becomes more problematic and costly when readings have to be collected from vast, and often scattered rural areas. Few years ago, the defunct Nigerian Electric Power Authority (NEPA) embarked on and commissioned the Scientific Control and Data Acquisition (SCADA) project that now enhances its ability to acquire data from the Grid, effect switching operations from distance. Later the Supply Authority went ahead to meter its transmission stations with a view to ascertaining the flow and quantity of energy. This was followed immediately by the monetization process of energy delivered to each Business Unit and the exercise created a challenge to minimize all kinds of energy losses in the system (Nwaoko, 2006). 146

2 In taking up the challenge, The Power Holdings Company of Nigeria (PHCN) has been exploring series of innovations for its present metering system. Such innovations include Automatic Meter Reading (AMR) and the Pre-payment Meter Scheme (Schwendtner, 1996; Jawarkar, 2008). These new ideas are targeted to reducing theft and other forms of avoidable losses in the system. The pre-payment meter which has been recently introduced in some parts of Nigeria uses Smart Card in dispensing energy. The stress of purchasing the smart card only from the Utility company; and lack of feedback mechanism after loading or during power theft are major setbacks. These drawbacks of the present prevailing metering systems are motivations into this work. This will keep track of the consumers load on a timely basis, which will help assure accurate billing, track maximum demand, detect and reduce power theft, provide a two- communication (feedback mechanism) for Power Utility ;and a prepaid GSM based Recharge scheme. Related work Shwehdi and Jackson (1996) in their paper, presented the Digital Tele-wattmeter System as an example of a microcontroller- based meter. The meter was implemented to transmit data on a monthly basis to a remote central office through dedicated telephone line and a pair of modems. It is only a stand- alone metering system. Zhang, Oghanna and Bai (1998) utilized a DSPbased meter to measure the electricity consumption of multiple users in a residential area. A Personal Computer (PC) at the control centre was used to send commands to a remote meter, which in turn transmitted data back, using the power Line Communication (PLC) technique. The major problem with this system is that it cannot detect tampering by consumers. Koay, Cheah, Sng, Chong, Shun and Tong (2003) in their work, designed and implemented a Bluetooth energy meter where several meters are in close proximity, communicated wirelessly with a Master PC. Distance coverage is a major set-back for this kind of system because the Bluetooth technology works effectively at close range. 147 In their paper, Scaradozzi and Conte (2003) viewed home- automation systems as Multiple Agent Systems (MAS). Home automation system was proposed where by home appliances and devices are controlled and maintained for home management. It is only a home management system and does not measure the amount of energy consumed by users. Hong and Ning (2005) in their paper, proposed the use of Automatic Meter Reading (AMR) using wireless networks. Some commercial AMR products use the internet for data transmission. Stanescu, Ciubotaru-Petrescu, Chiciudean, and Cioarga (2006) present a design and implementation of SMS -based control for monitoring systems. The paper has three modules involving sensing unit for monitoring the complex applications. The SMS is used for status reporting such as power failure. Issues on billing system for electricity board usage were not considered. Prepaid meters can also make use of state of art technologies like WiMAX owing to the idea of centralized accounting, monitoring and charging. It brings telecommunication to the core of its activities to support more Smart Grid applications such as Demand Response and Plug-in electric vehicles (Khan et al, 2007). Prepayment polyphase electricity metering systems have also been developed consisting of local prepayment and a card reader based energy meter (Ling et al, 2010). Malik, Aihab and Erum (2009) in their paper, mainly focused on the controlling of home appliances remotely and providing security when the user is away from the place using an SMS- based wireless Home Appliance Control. In their paper, Maheswari and Sivakumar (2009) aimed to develop an energy efficient and low cost solution for street lighting system using Global System for Mobile communication [GSM] and General Packet Radio Service [GPRS]. The whole set-up provides the remote operator to turn off the lights when not required, regulate the voltage supplied to the streetlights and prepare daily reports on glowing hours Sharma and Shoeb (2011), in their paper suggested a method where we utilize telecommunication systems

3 for automated transmission of data to facilitate bill generation at the server end and also to the customer via SMS, . Amit and Mohnish (2011) Suggested in their paper, a prepaid energy meter behaving like a prepaid mobile phone. The meter contains a prepaid card analogous to mobile SIM card. The prepaid card communicates with the power utility using mobile communication infrastructure. Once the prepaid card is out of balance, the consumer load is disconnected from the utility supply by the contactor. The power utility can recharge the prepaid card remotely through mobile communication based on customer requests. System structure The system structure of a Robust Prepaid Energy Metering System (RPEMS) is shown in fig.1. The Networked meter-reading system consists of GSM- Based Energy Meter, Power Utility Control Centre (PUCC) and GSM communication network. GSM-Based Energy Meter consist of a GSM Base Embedded Module (GBEM), which is the brain for the power data processing, tamper detection, and GSM- based recharge scheme (Prepaid billing). Power Utility Control Centre has a main computer or a network of computers, which contains the database of all installed meters. GSM Communication network, provides a two-way communication mode between the GBEM and PUCC. Figure 1 shows the System structure. Fig.1: System Structure GSM based energy meter The GSM-based energy meter mainly consists of two major parts : Energy Meter and GBEM. The Energy meter consist of the following :Energy Measuring Module (EMM), a Liquid Crystal Display (LCD), an Electrically Erasable Programmable Read Only Memory (EEPROM), Real Time Clock (RTC). The GBEM consist of the following: the microcontroller unit, Tamper detection unit, Latching Relay (LR) and a GSM modem. The Energy meter and GBEM are seen as one because they are strongly interfaced together to achieve the overall functions as stated as follows: i) Measurement of Energy Parameters.ii) Tamper detection ( iii) prepaid billing. Microcontroller unit PIC 18F2550 Microcontroller is used in this work. The firmware inside the microcontroller s program memory is built using two layers the Driver Layer and the Application Layer. The Driver Layer contains protocols for accessing different hardware peripherals such as LCD, EEPROM, EMM, RTC, LR, GSM modem, etc. On the top of the Driver Layer, the Application Layer contains routines for load calculation, bill calculation, data SMS frame creation etc. Application Layer calls different routines of the Driver Layer to access hardware peripherals. 148

4 Display unit: A 16 x 2 character LCD (HD44780) is interfaced with the microcontroller port using 4 data wire mode. Different meter readings like current month kwh, total kwh, voltage, current, data time, etc are sequentially displayed here. Permanent data storage Unit: If power fail occurs, the content of the RAM must be stored in EEPROM so that when power in back, the meter can start from its last state. An (AT24C164). EEPROM Also, different billing stabs containing rates for peak and off peak hour, meter ID etc are stored here. Real time clock: An RTC is used to get the current data and time information. The RTCF has a lithium battery inside it which is used to run the clock even if the power is off. Energy measuring module: The energy measuring module (ADE7756) is used to get the voltage, current, power factor, kwh, etc information of the connected single phase load. A Current Transformer (CT) and a potential Transformer (PT) are connected with the EMM to sense the current and voltage respectively. The microcontroller gets different information by reading different resister values of the EMM. Relay unit: a latching relay (LR) is used for connecting and disconnecting power supply to the Fig.2: GSM-based Energy Meter 148 customer s load. The microcontroller sends signals to the LR input signal pins to control the relay contacts. GSM modem: A wavecom GSM modem is interfaced with the micro-controller s serial (RS232) port for sending and receiving SMS. Using the FBUS protocol the microcontroller sends different commands to the modem and receives data SMS frames from the GSM modem. The serial communication with the modem is full duplex 8 bits, no parity, 1 stop bit and at bauds. Tamper detection unit: If any unauthorized person tries to open the meter box even if the meter has no power, the tamper detection unit will activate using a 4.5 volt battery and the meter will not let any current to flow to the customer. An SMS is automatically sent to the central sever reporting temper. The following events are also considered for tamper detection by the method. i) Missing potential event. ii) Current unbalance event.iii) Current reversal event GSM based recharge module: Pre-paid scratch-card based billing scheme can also be implemented using the SMS based technique. The electric supplier will produce scratch-cards and distribute them to local shops. Customers will buy scratch-cards from their

5 nearby shop and then send a special SMS using their personal cellular phone to the central server consisting of thecustomer s meter ID and the scratchcard s secret pin number. When the central server receives the SMS, it checks the validity of the meter ID and the pin number from the database. If the meter ID is valid and the pin number is also valid and still unused, then the server gets the customer meter s GSM modem call number from the database and sends an encrypted SMS to the customer s meter which contains the information of how much balance will be recharged in the meter. The meter receives the SMS, decode it and recharge the balance. Then it sends an acknowledgement SMS to the server indicating whether the balance is successfully recharged or not. After receiving the acknowledgement from the meter, the server then sends a report SMS to the customer personally. Server at the power utility control centre The Data Collection Module communicates with the GSM modem using FBUS protocol. When the server wants to collect information from a particular remote meter, it sends a Request SMS massage to the target meter and then waits for data from the GSM modem. After the remote meter receives the Request SMS massage, it makes a data frame consisting of the meter s information and sends it to the server by SMS. The server then gets the SMS data from the GSM modem and stores the information in the Database. Sometimes SMS massages are not delivered by the GSM network. We have developed the protocol such that if data SMS is not received after one minute, the server sends another request massage to the meter and waits for the data. In this way, the server makes total three attempts. If data SMS is not received in three attempts, the sever shows network error massages. The PUCC server is shown in Figure 3. The data collection can be done at any time or periodically such as hourly, daily, weekly or monthly basis. The Monitoring & Analysis Module gets data from the Database and calculates the overall energy consumption patterns of the meter. If any unexpected energy consumption pattern occurs, Fig.3: GUI of PUCC Server warning massages are generated and the sever operator can send Disconnection SMS massage to the remote meter to disconnect the meter s relay contacts and thus stop the customer to consume further energy. Experimental results An SMS based remote metering system prototype is developed and several experiments have been conducted (Wasi-ur-Rahman,2009). The total time taken to get a data SMS from the remote meter to the central server is approximately 30 seconds. This time may vary a little bit depending upon the GSM network condition. In an experiment, for 95% cases, data SMS was received successfully by one attempt. For the remaining 5% cases, data SMS was received after second or third attempt. Figure 4 shows a graph plot of consumed power of a consumer. The graph is generated by the central server based on the remotely received data. Fig. 5 shows the results obtained from a related work. Linear loads were varied from 340w to 2800w. The measurements were taken on the same day, in 1-minute intervals, each of 15 minutes duration i.e. for each load the power consumption values were transmitted from the meter each minute, and the readings were recorded for 15 minutes.these test were also performed on different days for determining the correlation of the results(nair and Maharaj,2004).. Results obtained shows good system performance. 150

6 Fig 4. A Graph Plot Generated by the Center (Wasi-ur-Rahman,2009). Fig.5:The ratio of the power error for various resistive loads (Nair and Maharaj,2004). Conclusion In this paper, a Robust prepaid energy metering system has been proposed for use in Nigeria. Different hardware and firmware unit of the metering system is described. The central server s different 150 modules and the communication protocol with the consumer s meters is also shown. Several data and results have been analyzed and reviewed. The system has many significant excellences, such as wireless, low-workload, great quantity of data

7 transmission high-veracity and low-expenses. The using of embedded system improves the stability of wireless data transmission. For a long distance transmission GSM telecommunication has shown excellent performance at any conditions. The implications of being able to transmit meter reading more often are that energy utilities will better understand energy demand patterns for network dimensioning and Demand Side Management (DSM), maintain meter failures more efficiently and manage fraud better. The entire system can be cost effective and significant amounts of time and money can be saved, by implementing an automated systems, as opposed to one involving the human element. The system also poses much less of a safety risk since human interaction has been minimized. Indeed this is an ideal system for use in Nigeria Reference Amit. J and Mohnish (2011). B- A Prepaid Meter using mobile communication International Journal of Engineering, Science and Technology-Vol. 3, No. 3, 2011, pp Hong. L and Ning.L (2004). Design and Implementation of Remote Intelligent Management System for City Energy Resources base on Wireless Network. Study of Computer Application 12: Jawarkar, N. P, Ahmed, V, Ladhake, S. A and Thakare, R. D (2008). Micro-controller based Remote Monitoring using Mobile through Spoken Commands. Journal of Networks 3: Koay.B.S, Cheah.S.S, Sng.Y.H,Chong. P.H.J, Shun.P,Tong.Y.C (2003). Design and implementation of a Blue tooth energy meter. proceedings of the Joint 4 th International Conference on Information, Communication and Signal Processing and the 4 th Pacific Rim Conference on Multimedia.3: Maheswari, C; Jejanthi, R (2009). Implementation of Energy Management Structure for street Lighting System. A Journal of Modern Applied Science 5:6-10. Malik S.H.l, Aihab. K, and Erum.S (2009). SMS Based Wireless Home Appliance Control System (HACS) for Automating Appliances and Security. Issue in informing Science and Information Technology 6: Nair, L.R and Maharaj, B.T(2004)-Efficient Digital GSM/GPRS Metering for Rural Electrification. pdf/c01.5% %29.accessed Nwaoko K. J. (2006). Electrical Energy Accounting Methods, Lagos: Impressed Publishers. Scaradozzi, D and Conte, G. (2003). Viewing home automat ion systems as multiple agents systems. RoboCUP2003, Padova, Italy. Retrieved from BOCUPSITOSIRI/articles/pdf/Conte.pdf Schwendtner.M.F (1996). Technological developments in electricity metering and associated. proceedings of the 8 th International Conference on Metering and Tarriffs for Energy Supply 8: Sharma.S and Shoeb.S. (2011)- Design and Implementation of wireless automatic meter reading system. International Journal of Engineering Science and Technology (IJEST)- Vol. 3, No. 3,March 2011, pp Shwehdi.M.H and Jackson.C (1996). A microprocessor based digital wattmeter system design. proceedings of the 31 st Intersociety Conference on Energy Conversion Engineering 31: Stanescu, D, Ciubotaru-Petrescu, B., Chiciudean, D., Cioarga, R.. (2006). Wireless Solutions for Telemetry in Civil Equipment and Infrastructure Monitoring. 3rd Romanian- Hungarian Joint Symposium on Applied Computational Intelligence (SACI). Retrieved from 152

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