In the age of ecological awareness, and the conclusion that energy should not be wasted, it is necessary to investigate the places where electrical energy is consumed. The effective energy usage of a device can often be determined by monitoring the according electrical devices over a long space of time. The measuring can easily be done by simple Energy Meters from the local do-it-yourself store. An energy meter is a device that measures the amount of electrical energy that is being consumed by a residence, business, or an electrically powered device. Electric meters are typically calibrated in billing units, the most common one being the kilowatt hour. Present energy meter reading is a tedious and an expensive affair as it requires manual collection of reading which is erroneous.Automatic Electric Meter reading is one method reading and processing data automatically with computer and communication.
It not only may relieve reading person’s labor intensity, reduce the reading mistake, but also has the advantage of high speed and good real-time. The project of the wireless Electric Meter reading for wireless communication technology completes the design of automatic Electric Meter reading system. There the data can be interpreted and may be even compared to data from other wirelessly connected devices.
Through researching the characteristic of main wireless communication protocol, ZigBee is chosen as lower layer communication protocol. ZigBee is a specification for a suite of high level communication protocols using small, low-power digital radios based on an IEEE 802 standard for personal area networks. The standard of ZigBeeis optimized for low data rate, low power consumption, security and reliability. Wireless energy meter using ZigBee is very useful for accurate energy billing apart from intelligent load shedding and theft detection.
Electricity is the driving force behind the development of any country. With the rapid increase in residential, commercial, and industrial consumers of electricity throughout the world, it has now become imperative for utilities companies to devise better, non-intrusive, environmentally-safe techniques of gauging utilities’ consumption so that correct bills can be generated and invoiced. The electricity system is one of the most important infrastructures in the modern society because it is the electrical power source of the electrical machines, e.g. motors and generators, used in the factory and also for the electrical appliances and lighting in households. Recently, an automation system has been applied to many basic infrastructures such as electricity, gas, and water systems in order to facilitate the routine work such as a manual control and a unit recording operation.
Nowadays, the unit recording has to be done by human before the end of each month. Since the unit recording was done by human, the human error becomes the major problem of system. Recently, the smart meter concept has been popularly adopted by many leading electricity companies in USA and EUROPE in order to overcome the problem of human error in the unit recording as well as provide the automatic procedure to report the energy meter impairment and the tampering activity of misbehaved subscribers by using the advance wireless and wired communication technologies.
To improve the efficiency and accuracy of metering systems, Automatic Meter Reading (AMR) system has been discussed and used for a long time. AMR is the technology of automatically collecting data from energy metering devices (water, gas, electricity etc.) and transferring the data to a central database for billing and/or analyzing. This means that billing can be based on actual consumption rather than an estimate based on previous consumption, giving customers a better control of their use of electric energy, gas usage, or water consumption. In this paper, a design and implementation of wireless sensor network and protocol for smart energy meter is proposed.
NEED FOR PROPOSED SYSTEM
2.1 Electro Mechanical Type Energy Meter
An energy meter is a device used to measure the amount of energy supplied to a particular load. Most commonly energy is measured in Kilowatt Hours (KWH). The present energy billing system in India uses both electromechanical energy meters and digital energy meters. The most traditional and widely used energy meter is the electromechanical energy meter. This energy meter works on the principle of electro-magnetic induction.
Fig 2.1 Electromechanical Energy Meter
The construction of an electromechanical energy meter consists of three electrical circuits, magnetically coupled, two of them fixed and one rotating around the mechanical axis of the system. The two fixed circuits are the voltage and the current coils. The third circuit is the Aluminium rotating disk which is mounted on a rigid axis. When the aluminium disk rotates, the disk axis will transmit the disk rotation to a mechanical counter which provides the energy display. 2.2 Digital Energy Meter
Fig 2.2 shows a block diagram of digital energy meter. In Fig 2.2, the alternating current (AC) is supplied through the current transformer (CT) and the potential transformer (PT) so that any sudden changes in the voltage and currents will not affect the energy meter. These transformers also step down the voltage and the current to circuit levels.
The output of the CT and PT is supplied to Energy Meter IC which generates the pulses according to the energy supplied to it. Software burned on to the microcontroller performs the usage calculations. The LCD display is used to display the number of units consumed by the consumer. The digital energy meter has solved many of the problems with Electro-Mechanical Energy Meter. The major disadvantage of the digital energy meter is that it does not address the billing which is a labor consuming process.
Fig 2.2 Digital Energy Meter
2.3 Proposed System
The proposed system, as shown in Fig 2.3 consists of three main modules: Consumers’ Digital Energy Meter, Communication System and Base Station.
Fig 2.3 Proposed System
Base station is the place where all the energy meters, which are interconnected through network, are controlled with the help of specific software. Communication system is used to connect the energy meter and the base/control station. There are several communication methods like communication using RF transceivers, GSM etc. Here, we have to follow wireless protocol to avoid collision and confusion. ZigBee is the most recent advancement of the wireless standards used.
ZigBee is a wireless networking standard that is aimed at remote control and sensor applications. It is a specification for a suite of high level communication protocols using small, low-power digital radios based on an IEEE 802.15.4 standard for personal area networks, which defines the Physical and MAC layers. ZigBee devices are often used in mesh network form to transmit data over longer distances, passing data through intermediate devices to reach more distant ones. This allows ZigBee networks to be formed ad-hoc, with no centralized control or high-power transmitter/receiver able to reach all of the devices. ZigBee is targeted at applications that require a low data rate, long battery life, and secure networking. ZigBee has a defined rate of 250 Kbit/s, best suited for periodic or intermittent data or a single signal transmission from a sensor or input device.
Applications include wireless light switches, electrical meters with in-home-displays, traffic management systems, and other consumer and industrial equipment that requires short-range wireless transfer of data at relatively low rates. The technology defined by the ZigBee specification is intended to be simpler and less expensive than other WPANs, such as Bluetooth. It is also suitable for operation in harsh radio environments and in isolated locations. ZigBee operates in the industrial, scientific and medical (ISM) radio bands; 868 MHz in Europe, 915 MHz in the USA and Australia, 2.5 GHz in India and 2.4 GHz in most jurisdictions worldwide. Data transmission rates vary from 20 to 900 kilobits/second.
3.1 ZigBee Protocols
ZigBee protocol uses DSSS (Direct-Sequence Spread Spectrum) technology, because the alternative FHSS (Frequency-Hopping Spread Spectrum) uses too much power just to keep its frequency hops synchronized. In DSSS, even if one or more chips in the chip pattern, which carry data, are damaged during transmission, the original data can be recovered without the need of retransmission. The protocols build on recent algorithmic research (Ad-hoc On-demand Distance Vector, neuRFon) to automatically construct a low-speed ad-hoc network of nodes. In most large network instances, the network will be a cluster of clusters. It can also form a mesh or a single cluster. The current ZigBee protocols support beacon and non-beacon enabled networks.
Fig 3.1 Zigbee Protocol Stack
The ZigBee protocols minimize the time the radio is on, so as to reduce power use. In beaconing networks, nodes only need to be active while a beacon is being transmitted. In non-beacon-enabled networks, power consumption is decidedly asymmetrical: some devices are always active, while others spend most of their time sleeping. 3.2 Device Types
Zigbee devices are of three types:
* ZigBee End Device (ZED): End devices can be start or destination of a message, but cannot forward messages for other devices. It contains just enough functionality to talk to the parent node (either the coordinator or a router); it cannot relay data from other devices. This relationship allows the node to be asleep a significant amount of the time thereby giving long battery life. A ZED requires the least amount of memory, and therefore can be less expensive to manufacture than a ZR or ZC. * ZigBee Router (ZR): Routers can be the start or destination of a message, and also can forward messages for other devices. As well as running an application function, a router can act as an intermediate router, passing on data from other devices.
They can extend network area coverage, dynamically route around obstacles and provide backup routes in case of network congestion or device failure. * ZigBee coordinator (ZC): The most capable device, the coordinator forms the root of the network tree and might bridge to other networks. There is exactly one ZigBee coordinator in each network since it is the device that started the network originally. They are special type of routers having an added intelligence allowing them to store and manage information about the network, including acting as the Trust Center and repository for security keys. They can also provide Gateway functionality.
3.3 Beacon Oriented Networking
In beacon-enabled networks, the special network nodes called ZigBee Routers transmit periodic beacons to confirm their presence to other network nodes. Nodes may sleep between beacons, thus lowering their duty cycle and extending their battery life. Beacon intervals depend on data rate. However, low duty cycle operation with long beacon intervals requires precise timing, which can conflict with the need for low product cost. In beaconing networks, nodes only need to be active while a beacon is being transmitted. In general, the ZigBee protocols minimize the time the radio is on, so as to reduce power use.
The basic channel access mode is ‘Carrier Sense, Multiple Access/Collision Avoidance’ (CSMA/CA). That is, the nodes talk in the same way that people converse; they briefly check to see that no one is talking before they start, with three notable exceptions. Beacons are sent on a fixed timing schedule, and do not use CSMA. Message acknowledgments also do not use CSMA. Finally, devices in Beacon Oriented networks that have low latency real-time requirements may also use Guaranteed Time Slots (GTS), which by definition do not use CSMA.
4.1 Consumer Side Unit
The general block diagram for the transmitter part (Consumer side) of the network is shown in Fig 4.1
Fig 4.1 Block Diagram Of The Transmitter
4.1.1 Power Supply
Almost all electronic equipment includes a circuit that converts AC voltage of main supply into DC voltage which is called power supply. Its input is a power transformer and output then fed to a Rectifier circuit. The output of the rectifier goes to a smoothing filter, and then to a voltage regulator circuit that provides a regulated constant DC power supply.
4.1.2 Pulse Detector
Pulse detector circuit is used to obtain the electrical units consumed, from energy meter and convert them into digital pulses using optocoupler (MCT2E).These pulses are given as an external interrupt to the microcontroller.
Microcontroller is the central processing unit, which controls all the functions of other blocks explained here. It takes or read data from the energy meter and controls all the functions of the whole system by manipulating these data. Microcontroller is interfaced with the ZigBee device using a suitable interfacing.
4.1.4 Display Section
LCD display is used for displaying the state of the unit. LCD module is a dot matrix liquid crystal display that displays alphanumeric, kana (Japanese character) and symbols. The built in controller and driver LSI, provide convectional connecting between LCD and most 4 or 8 bit microcontroller. The CMOS technology makes the device ideal for applications in handheld portable and other powered instruments with low power consumptions.
4.1.5 ZigBee Module (XBee PRO)
ZigBee is a wireless technology developed as an open global standard to address the unique needs of low-cost, low-power, wireless sensor networks. It is based IEEE 802.15.4 Standard. To increase the range of transmission, a number of ZigBee devices, called as nodes are wirelessly connected into a network and are controlled using the microcontroller located at the Utility Service Provider Stations.
4.2 Authority Side Unit
Fig 4.2 Block Diagram Of The Receiver
The signals that are sent from the various energy meters in a region connected through a ZigBee network are received by the ZigBee Coordinator and the readings are transferred to the microcontroller. The microcontroller reads and store data for billing purposes. The main advantage of a ZigBee device is that the same device can act as both transmitter and receiver as and when required. So the requirement for separate transmitter and receiver is not essential.
IMPLEMENTATION OF NETWORK
Recent advances in wireless communications standards and energy-efficient technologies have made it possible to effectively combine ZigBee nodes create reliable, large-scale wireless lighting networks. This provides enhanced control and reductions in energy consumption for domestic as well as commercial and industrial buildings. This reduction translates into significant cost and energy savings. To deliver effective and affordable energy management, a variety of network topologies are implemented for combining different ZigBee nodes into a network. Topology refers to the configuration of the hardware devices that make up a network and how the data is transmitted through that configuration. Fig 5.1 shows some of the more popular network topologies in use today.
Fig 5.1 ZigBee Network Topologies
5.1 Different Topologies for ZigBee Network
There are different network topologies that can be adopted for building up a wireless ZigBee network. As in Fig 5.1, star networks can be used for its simplicity. Mesh or peer-to-peer networks enable high degree of reliability. Cluster tree networks are multiple star networks organized by coordinator. Cluster tree networks can be used, as it is a close communication within the node in the same region, data transmission has great redundancy, so taking clustering structure of the network, and distributing centralized nodes to form clusters and elect cluster head. A cluster tree network is basically multiple star networks organized by coordinator. The coordinator is responsible for starting the network and for choosing certain key network parameters.
End device nodes communicate not only with the coordinator but also communicate with every router nodes. The router nodes process a routing function and can only communicate with the coordinator. A mesh network provides high reliability networks. Mesh networks are preferred and widely used as the router node in the mesh network not only perform a routing function but also communicate with other nodes. Unlike mesh, the other topologies do not offer alternative routes through the network.
That means that if one of the network devices fails or suffers congestion, network traffic will slow and may even stop. It is not acceptable for many applications like energy provision and management, commercial building automation, lighting control, and industrial automation all require high levels of reliability and resiliency. Mesh networks lend themselves to large, complex networking applications with many devices.
5.2 Wireless Mesh Benefits
Removing the wires provides a number of benefits over wired mesh networking: • Flexibility: The physical placement of a wireless mesh device is extremely flexible—as long as it is within communications range of other devices within the network, it can be placed nearly anywhere. Areas that would be difficult, expensive, or even impossible to cover within a wired network are accessible within wireless networks. • Cost: Wireless removes the expense and time involved in installing and maintaining dedicated wiring to each device within the network. This makes wireless mesh a very affordable solution for retrofit applications, in that it removes the need (and associated costs and disruption) to run new wiring through existing walls and ceiling spaces.
• Scalability: A single mesh network can support thousands of individual devices. Adding new devices can be as simple as putting the device where you want it, and then turning it on. • Reliability and robustness: A mesh network can be improved in many ways by adding more devices – extending distance, adding redundancy, and improving link quality and the general reliability. This is particularly easy with wireless networks, where administrators can add, move and remove devices without needing to perform elaborate site surveys or worry about wiring to communicate between devices.
ZIGBEE OVER OTHER WIRELESS NETWORKS
ZigBee is an open standard that was created to address the market need for a cost-effective, standards-based wireless networking solution that supports low data-rates, low-power consumption, security and reliability. This makes it ideal for a wide set of machine-to-machine and control applications such as commercial building and home automation, lighting control, energy management and telecommunication services. The robustness of the ZigBee standard, combined with the benefits of wireless mesh networking, make ZigBee ideally suited for commercial building automation and lighting control solutions. The major advantages of a Zigbee based wireless energy meter are: * Improved operational efficiencies: The wireless meters are likely to cut the cost of meter reading than the conventional meters, as no meter readers are required. In addition, they eliminate administrative hassles associated with disconnection and reconnection.
* Reduced Chance of Meter Tampering: Wireless energy meters have built in tamper detection facility which eliminates any chance of mechanical tampering. * Better Energy Management: Since the load pattern of a particular area and customers is available through the database, it facilitates load shedding in case of energy shortfall. The system will enable easy energy audits. * Reduction in Power Theft: Because of the real time theft detection system and automatic re-routing by the mesh network routers, power thefts can be drastically reduced or removed. * Data Collision Avoidance: Although all meters work at same wireless frequency, data collisions between different meters will not occur due to the efficient mesh networking protocol used for data transmission on wireless media.
* Increased System Reliability: In this design many meters function on the same frequency, so that all power information can be collected at a centralized single point. The same transmitter allows the line voltage, line current and other measurements at various points to be monitored by the centralized station. This data can be used in load shedding and fault analysis. The fault location can be easily found out using this type of arrangement and fault clearance time can be drastically reduced, thereby increasing system reliability.
ZigBee technology is a new wireless technology that is widely used in various applications because of its excellent performance in reliability, capability, flexibility and cost. Also the power requirement for a Zigbee device is very less and this can make it useful in longer distance transmission at the expense of no or less power. The main intention of this paper was to investigate the possibilities of a ZigBee based wireless energy meter in improving the efficiency and accuracy of electrical metering systems by reducing electricity measuring errors. The current system enables residents to have an immediate overview about the actual and short term history power consumption. For the consumer this offers the possibility for getting direct information about better pay scales or to let the provider dynamically change the pay scale.
Metering and monitoring of other utility commodities such as Internet access, prepaid drinking water, gas etc., can be implemented using ZigBee. Future work will include developments towards automatic and remote control of devices. A further approach could be that once a day accumulated data is sent from the household to the energy provider. This gives the energy provider the opportunity to better calculate the needed capacities of their power plants. It can be easily implemented anywhere and unobstructed by the geographical factors, as ZigBee devices are least prone to external disturbances.
Despite its simplicity, a uniform wireless smart meter network is actually more expensive to run and offers few or no revenue opportunities to a utility to offset the cost of installation. Concern is increasing, though, that ZigBee could turn into a one-size-fits-all technology that doesn’t fit any application particularly well. Setting aside the cost factor, meter readings can be effectively automated using Zigbee as proven byUSA and Europe. The time is not so far when Indian meters will “tell” the consumer to remit their electricity bills.
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