USE OF GSM/GPRS TRANSMISSION TO MONITOR THE MECHANICAL PARAMETERS OF A SMALL WIND TURBINE OF UP TO 10kW

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1 Advances in Computer Science and Engineering Volume, Number, 2011, Pages This paper is available online at Pushpa Publishing House USE OF GSM/GPRS TRANSMISSION TO MONITOR THE MECHANICAL PARAMETERS OF A SMALL WIND TURBINE OF UP TO 10kW VILSON GRUBER, DIEGO RODRIGUES FERREIRA, SÉRGIO DEITOS BITTENCOURT, WAGNER CABRAL BORDIGNON and LÍRIO SCHAEFFER Faculdade SATC, Brazil vilson.gruber@satc.edu.br Universidade Federal do Rio Grande do Sul, Brazil diego.ferreira@ufrgs.br sergio.bittencourt@ufrgs.br wagner.bordignon@ufrgs.br schaefer@ufrgs.br Abstract This paper shows cellular communication technologies by creating a prototype of a data acquisition interface using the GSM/GPRS cellular network to simulate the transmission and reception of data for remote monitoring of 02 (two) variables defined here: tower vibration and brake pad wear, in a small wind turbine of up to 10 kw. The data studied here show results that may be useful for any business that plans to implement a remote monitoring system using the Cellular Network (GSM/GPRS). Although wind turbine variables are used in the experiment, other remote monitoring applications are possible using air communication channels, such as monitoring pollutant emissions, river and reservoir level alerts, landslide warnings, agricultural irrigation systems. Keywords and phrases: wind turbines, wireless, cellular networks (GSM/GPRS), remote monitoring. Received March 16, 2011

2 2 VILSON GRUBER et al. 1. Introduction Data transmission is an essential resource for different market sectors. Economic development and technological advance are creating the need for supervision and monitoring, and real-time information which is a determining factor in gaining new clients, managing resources and controlling the operation is becoming part of the strategy to survive in the market [1]. Systems in the SCADA model (Supervisory Control and Data Acquisition) enable this kind of control via data acquisition, remote and/or automatic transmission and actuation [2]. There is an increasing use of renewable energies such as wind generation. Conscientious countries are seeking to reduce CO 2 emissions; the energy revolution may become a reality [3], increasing our day-to-day comfort and using clean energies to lower consumption. In order to enable the use of renewable energy systems, we need these systems to be self-sufficient or to require minimal maintenance. Remote monitoring systems do this for instance, by providing distant management of one or more wind generation units. A great advantage already due to remote monitoring is to reduce unnecessary visits by maintenance staff. Currently different technologies are used for remote monitoring but for many the use of the air communication channel is still a paradigm [4]. This article is the result of a study on wireless data transmission for remote monitoring of variables. A system that simulates the functioning of a wind turbine was used and two variables were transmitted. One of them is the tower vibration sensor signal, and the other the brake pad wear signal, since the wind turbine being studied has a disc brake which wears down these pads. The study below can be used as a reference for several applications that require data transmission using the wireless system. An example of this is pollutant emission monitoring applications, river stages (floods), flood alerts (reservoir levels), watershed control, reservoir monitoring and landslide warnings. It can also be used for agricultural purposes, such as to obtain the weather forecast at remote sites. Also, irrigation systems can be controlled remotely in agriculture [5], [6]. 2. GSM/GPRS Systems The GSM (Global System for Mobile Communications) is the second generation

3 USE OF GSM/GPRS TRANSMISSION TO MONITOR 3 digital standard developed in Europe and used in most of the world [7]. It was initially developed for the 900 MHz wavelength and a version was later adapted for the 1800 and 1900 MHz wavelengths. One of the purposes of telecommunications systems standardization was to ensure that the user would have the service available in any part of Europe. (Paragraph One, definition). The terminals consist of a transceptor and SIM (Subscriber Identity Module) Card. Without the SIM Card the mobile station cannot receive or make calls, since it is not associated with any user. The SIM Card is a small chip that is used to store user data and their authentication code. The SIM Card can be disconnected from a transceptor and connected to another by the user himself, and it can also be used in any other GSM cell phone, since the data are stored on the chip. It is the SIM Card that provides the identity of the mobile unit, and the mobile terminal only operates when the SIM Card and transceptor are connected. The GSM standard is most used worldwide, since it has several technological innovations, such as international roaming among the countries of Europe, increased security (since the user authentication is performed at the terminal) and it has an open architecture (combination of equipment from different manufacturers). Generation second and a half These are cell systems that offer data services in packets without the need for a permanent connection [8]. It is an intermediate step to the third generation. The main systems are GPRS (General Packet Radio Services) and EDGE (Enhanced Data Rates Services) and HSCSD (High Speed Circuit Switched Data). GPRS (General Packet Radio Services) This is a basic service for GSM, which improves and simplifies access to data networks and transfers data packets between the mobile station and the data network [9]. GPRS solves the following problems: Transfer of the data in packets; Direct interconnection with IP networks; Greater flows (dozens of kbps); Low access time (< 1 s); Rating directed at the data.

4 4 VILSON GRUBER et al. In order to use the GPRS, the users basically require: a mobile telephone system or a terminal that can support GPRS; a subscription to a mobile telephony system that can support GPRS; have a licensed GPRS; knowledge on how to send and receive information by GPRS using a telephone, including hardware and software configurations, which require a customer service system; a destination to which to send or place to receive information through GPRS. The main characteristic of GPRS is to establish a data connection without the need to establish a phone circuit, which allows charging for use, not for time of connection, and the service is thus always available to the user. GPRS implementation requires small modifications of the installed structure, making it easier for GSM operators to adopt: It is standardized to transport data defined by IP and x.25 protocols. The Serving GPRS Support Node (SGSN) performs the logical connection of the mobile users when they go from the area covered by one cell to another (handover). Gateway GPRS Support Node (GGSN) allows internet connection. When a GPRS terminal is energized, it will be recognized by the network similarly to what occurs with a GSM voice terminal. Then a logical linkage is created between the terminal and the Serving GPRS Support Node (SGSN). An IP address must then be obtained establishing a connection in the GPRS. The IP address is supplied by the mobile operator. At this point the GPRS terminal is ready to send and receive packets. Classes of Terminals: Class A Terminals that can process voice and data at the same time Class B Terminals that can process voice and data, but not at the same time Class C Terminals that can only process data The GPRS terminal can be used directly for access to data or to the internet using WAP (Wireless Application Protocol), or it can be connected to another

5 USE OF GSM/GPRS TRANSMISSION TO MONITOR 5 equipment, such as a microcomputer. An example of connection in this case is Bluetooth. The connection between the operator and an external IP network is done through an APN (Access Point Name). The operator establishes APNs for several networks, one of them being typically defined for the public WAP network. The number of APNs supported by a terminal varies according to model and manufacturer. HSCSD (High Speed Circuit Switched Data) The HSCSD aims at increasing the basic GSM system data rate. The GPRS system cannot support all possible applications on the HDCSD. In order improve this it is only necessary to upgrade the software and to have new mobile terminals. As to the GPRS system, its best performance is in real time applications. EDGE (Enhanced Data rates for GSM Evolution) The basic idea of EDGE or Enhanced GPRS (EGPRS) is digital modulation. Only an upgrade of the Base Stations software is needed to use it in a GSM network. Digital modularization applied to EDGE, 8PSK (Eight-Phase Shift Keying) does not replace, but instead coexists with the modulation technique used in the GSM, GMSK (Gaussian Minimum Shift Keying). In this way the user can utilize the GSM terminals on an EDGE network. It is mandatory to keep GMSK, since 8PSK can only be used effectively over short distances. ECSD is a combination of EDGE and HSCSD and it allows three times higher rates than HSCSD. If EDGE is implemented on a GPRS network, the combination is known as EGPRS. The maximum data rate using all resources of the carrier, and if the Mobile Terminal is close to the base station, is 384 Kbps. EDGE can be introduced into the network gradually and sparingly. Initially it will only cover areas with a higher demand for data and services. The other areas can maintain the coverage with a GSM/GPRS signal, since the EDGE cell phones can also use this signal to transmit voice and data at lower rates. 3. Mechanical Monitoring of Wind Turbines The mechanical system of the wind turbine has different signals of interest, but this study focused on the analysis of the feasibility of monitoring brake pad wear and tower vibration.

6 6 VILSON GRUBER et al. For this purpose, a wind turbine with a motor simulating the primary machine (wind and blades was set up, as shown in Figure 1. Figure 1. Wind turbine bench tests. Tower vibration sensor The brake is configured for emergencies, but in isolated operation, it is additionally used as a regular brake. Regular brake means that it is used for normal braking processes which are often repeated. This happens when in an autarchic system the power generated cannot be absorbed, so that the machine must be switched off and braked. Emergency brakes only operate in cases in which there are casual interferences in normal operation by actuating the vibratory switch. The brake is also used for maintenance work. 4. Acquisition System The data acquisition board is an optimized model for simultaneous acquisition of data at different velocities. Generally it has A/D (analog/digital) converters, processors, RAM memory and a communication interface. A prototype of an acquisition board was designed for the system involved here. It talks with the GSM/GPRS modem according to the standard protocol of the manufacturing brand. It can be seen in Figure 2, together with the sensor simulators.

7 USE OF GSM/GPRS TRANSMISSION TO MONITOR 7 Figure 2. Data acquisition board. The serial port which will be used to communicate with the GSM/GPRS modem is seen in Figure Methodology The methodology applied in the tests was based on the diagram shown in Figure 3, where the sensing system communicates via modems GSM/GPRS and the cellular telephony network with a remote data supervision software. Figure 3. Communication via GSM/GPRS modem. Based on this system outline, it was defined that monitoring would be implemented using qualitative values for the variables analyzed, making it easier for the supervisory operator to understand the parameters. Figure 4 shows an example of how the supervisory works for the desired variables.

8 8 VILSON GRUBER et al. Modem Transmission Modem Reception Sensors Figure 4. Communications methodology studied. Since the supervision systems are directed toward people who do not know much about technical matters, it is essential for the data to be quantified qualitatively. As a test of the transmission system, the simulated sensors were used to evaluate its performance. In later iterations, the mechanical systems will be used for practical proof of supervision. 6. Results and Comparative Analysis It is known that wind turbines should be able to withstand all kinds of winds without losing control of blade rotation. If this happens the result will be extremely unpleasant noise, or even an accident in which the blades break. The tower is a component that can be highly variable depending on local conditions, terrain, wind barriers and area available to set it up. Monitoring these parameters is very important for the work life of this equipment. The more effective, safer control of these parameters will determine the successful use of this power generation equipment. These systems are usually chosen for economic reasons, and in some cases due to the technical complexity that leads to frequent maintenance. In order to prove the efficiency of the application

9 USE OF GSM/GPRS TRANSMISSION TO MONITOR 9 developed, online results of 02(two) parameters monitored via GSM/GPRS cellular network are presented. Figures 5a and 5b show online results of the tower vibration parameter, emphasizing that in Figure 5b the user is informed about the need to actuate the emergency brake: Figure 5a. Supervisory system without vibration. Figure 5b. Supervisory system with vibration.

10 10 VILSON GRUBER et al. Figures 6a and 6b show an example of monitoring information on brake pad wear: Figure 6a. Supervisory system showing brake pads in good condition. Figure 6b. Supervisory system showing worn brake pads.

11 USE OF GSM/GPRS TRANSMISSION TO MONITOR 11 Table 1 shows the economic comparison between the main technologies used: Table 1. Economic comparison between the most used technologies Technology Advantages Disadvantages Cost of Telecom Cost of Monthly Service Cellular Does not require Limit of coverage US$ per US$ (GPRS) investment in in some regions. machine infrastructure. Pricing system Private Economical for Needs license to Around US$500 None. Radio short distance operate. 2,500 per machine Frequency (UHF/VHF) applications (20Km- 40Km) Needs space for towers and retransmitters. (not counting the costs of towers and retransmitters). Low network capacity for data. Microwave Low cost for Relatively high US$10,000- None (for companies/clients costs to operate and 60,000 (fixed cost companies that who already have maintain of infrastructure) already have microwave systems (private networks). Needs license to operate. microwave system). Coverage problems Satellite Covers areas not High cost US$3,000-20,000 US$ per reached by other technologies. Needs license to operate. per transmission point month. 7. Conclusion The Study of Remote Monitoring Systems of a Wind Turbine via Wireless Transmission Network-Wireless provides greater control of the use of wind turbines installed not only in the laboratory for analysis, but also in all those that one wishes to monitor. Using a wireless transmission network the costs of investment in a possible implementation at remote sites can be reduced. It is known that most wind turbine

12 12 VILSON GRUBER et al. equipment is installed at sites where a cable transmission system would be very difficult to place, due to the request for authorizations to pass them through, implementation costs, servicing, and others. Traditionally, different communications media are used to support remote monitoring applications, including microwave systems, private radio, telephone lines, electricity grid, satellite and proprietary network systems. The choice of a specific communications network is mainly a function of area of coverage, price of solution and equipment, solution reliability and easy integration. The importance assigned to each of the factors depends on the need involved. A major factor which should be taken into account is the frequency of network use by each application. The benefits provided by most of the remote monitoring projects on the market are clear and significant. However, because of the current price of the solutions the cost/benefit ratio for most of the sectors is not worthwhile. However, it is important to emphasize that, depending on the sector the cost/benefit ratio may vary according to the number of points connected. In other words, it is essential to perform the individual analysis of each sector. Thus, the companies that manage to diminish the cost of applications and terminals will be able to encourage the adoption of these solutions and increase their participation in the market. As to the model of impact of prices per solution, the most crucial aspect is the fixed monthly price of the connection. No matter how much some solution providers offer a fixed and variable costs composition, a simplified model with only a fixed cost per point connected is suggested. This suggestion is due to the tendency for data transmissions to be predictable and sporadic, so that lower price models are more acceptable on the market. Exceptions must be made in the case of applications where there is greater complexity and a greater volume of information exchanged. In such cases the fixed/variable model still makes more sense.. References [1] Anteu Fabiano L. Gasparini et al., Redes Metropolitanas e de Longa Distancia: MAN, Campus e WAN Backbone Designer, 2. ed., Erica, Sao Paulo, 2008, 298pp. [2] Stuart A. Boyer, SCADA: Supervisory Control and Data Acquisition, Instrument Society of America, [3] GREENPEACE (Brasil), Revolução Energética: perspectiva para uma energia global sustentável, São Paulo, 2007, 7pp. Disponível em:

13 USE OF GSM/GPRS TRANSMISSION TO MONITOR 13 < Acesso em: 05 Mar [4] Virgílio Fiorese, Wireless: Introdução às Redes de Telecomunicações Móveis Celulares, Brasport, Rio de Janeiro, 2008, 336pp. [5] Muriel de Fátima Bernhardt, Microservidor Web no monitoramento e controle remotos da qualidade da água na carcinicultura, f. Dissertação (Mestrado) - Curso de Mestrado em Ciências da Computação, UFSC, Florianópolis, Disponível em: < Acesso em: 20 Mar [6] Antonio Marcio Paiva Mattos, Monitoramento Hidrológico - Via Telefonia, f. Dissertação (Mestrado) - Curso de Engenharia da Energia, Departamento de Engenharia da Energia, Universidade Federal de Itajubá, Itajuba, [7] W. C. Y. Lee, Mobile Cellular Telecommunications Systems, McGraw-Hill Book Company, New York, USA, [8] M. S. Alencar, Telefonia Celular Digital, Editora Érica, São Paulo, 2008, 448pp. [9] P. S. M. Bernal, Comunicações Móveis: Tecnologias e Aplicações, Editora Érica, São Paulo, 2008.

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