Acta Polytechnica doi:10.14311/AP.2013.53.0878 Acta Polytechnica 53(6):878–882, 2013 © Czech Technical University in Prague, 2013 available online at http://ojs.cvut.cz/ojs/index.php/ap A LIGHTNING CONDUCTOR MONITORING SYSTEM BASED ON A WIRELESS SENSOR NETWORK Jan Mikeša,∗, Ondrej Kreibichb, Jan Neužilb a Department of Economics, Management and Humanities, Faculty of Electrical Engineering, Czech Technical University in Prague, Technická 2, CZ-16627 Prague, Prague 6, Czech Republic b Department of Measurement, Faculty of Electrical Engineering, Czech Technical University in Prague, Technická 2, CZ-16627 Prague, Prague 6, Czech Republic ∗ corresponding author: mikes.jan@fel.cvut.cz Abstract. Automated heating, lighting and irrigation systems are nowadays standard features of industrial and commercial buildings, and are also increasingly found in ordinary housing. In addition to the benefits of user comfort, automated technology for buildings saves energy and, above all, it provides enhanced protection against leakage of water and hazardous gases, and against fire hazards. Lightning strikes are a natural phenomenon that poses a significant threat to the safety of build- ings. The statistics of the Fire and Rescue Service of the Czech Republic show that buildings are in many cases inadequately protected against lightning strikes, or that systems have been damaged by previous strikes. A subsequent strike can occur within the period between regular inspections, which are normally made at intervals of 2–4 years. Over the whole of Europe, thousands of buildings are subjected to the effects of direct lightning strikes each year. This paper presents ways to carry out wireless monitoring of lightning strikes on buildings and to deal with their impact on lightning conductors. By intervening promptly (disconnecting the power supply, disconnecting the gas supply, sending an engineer to inspect the structure, submitting a report to ARC, etc.) we can prevent many downstream effects of direct lightning strikes on buildings (fires, electric shocks, etc.) This paper introduces a way to enhance contemporary home automation systems for monitoring lightning strikes based on wireless sensor networks technology. Keywords: lightning protection, lightning monitoring, wireless sensor networks, lightning counter sensor node. 1. Introduction Lightning discharges are highly unpredictable and un- controllable natural phenomena, and their direct and indirect effects can have destructive consequences for structures. Due to the low probability of a strike, owners and managers of buildings often neglect to en- sure that they are safely protected from direct light- ning strikes. The building is thus exposed to the risk of being struck by a lightning current without any protection. Other buildings are located in places where lightning strikes so frequently that a direct hit on the building is almost inevitable, and may even be repeated several times a year [1]. The only currently used protection systems for res- idential, commercial and industrial buildings involve conducting lightning discharges from the point of the strike through the catchment system safely into the ground. Safe operation of this system depends on the condition in which it is maintained. Statistics [2] in- dicate that a direct lightning strike can cause a fire or, more commonly, can destroy electrical appliances and consumer electronics even in a building with a protective conductor [3]. Our study addresses the issue of monitoring light- ning strikes on buildings and processing this informa- tion online. A direct lightning strike can discharge a current of tens to hundreds of kA. The strike can have a considerable dynamic and thermal impact on com- ponents of the protection system. All kinds of me- chanical joints are vulnerable. The conductive con- nection to the grounding system may be damaged, and the conductors and the catchment equipment it- self may be mechanically and thermally damaged. Regular inspections of the lightning conductor sys- tem are covered in Annex E of ČSN EN 62305-3 ed. 2, which specifies periodic inspections at intervals of 2–4 years. The time intervals are defined according to the protection classification of the structure (commercial buildings are mostly in class II and class III) based on an analysis of the risk of harm as defined in ČSN EN 62305. In the Czech Republic, the applicable proce- dures are the ČSN EN 33 1500 standard with a valid change of Z4 and default inspection of ČSN 33 2000- 6-61 ed.2 (332000) Electrical installations of buildings – Part 6-61: Revision – Initial revision. The ČSN EN 62305 standard is a translation of the European stan- dard, so equivalent rules apply in the countries of the European Union. However, experience suggests that an interval of 2 to 4 years between inspections may be too long. When a building, its lightning conduc- tor and grounding system are struck by lightning, the 878 http://dx.doi.org/10.14311/AP.2013.53.0878 http://ojs.cvut.cz/ojs/index.php/ap vol. 53 no. 6/2013 A Lightning Conductor Monitoring System Protection Visual inspection Complete inspection Critical situationsa level Complete inspectionb Year Year Year I and II 1 2 1 III and IV 2 4 1 a Lightning protection systems utilized in applications involving structures with a risk caused by explosive materials should be visually inspected every 6 months. Electrical testing of the installation should be performed once a year. An acceptable exception to the yearly test schedule is in order to perform the tests on a 14 to 15 month cycle where it is considered beneficial to conduct earth resistance testing over different times of the year to get an indication of seasonal variations. b Critical situations could include structures containing sensitive internal systems, office blocks, commercial buildings or places where a large number of people may be present. Table 1. Maximum period between inspections of a Lightning Protection System adopted as IEC 62 305-3 [4]. Year Cause Number Ratio Damage Ratio Fatalities Injuries of fires [%] [thousands of CZK] [%] 2012 lightning – W 13 0,06 8 953,0 0,31 0 1 lightning – WO 30 0,15 10 727,0 0,37 0 5 2011 lightning – W 14 0,07 26 159,7 1,17 0 0 lightning – WO 31 0,15 18 994,5 0,85 0 5 2010 lightning – W 13 0,07 3 041,00 0,16 0 0 lightning – WO 24 0,13 6 912,30 0,35 0 3 2009 lightning – W 12 0,06 2 067,0 0,10 0 1 lightning – WO 29 0,14 14 700,5 0,68 0 1 2008 lightning – W 9 0,04 1 385,00 0,04 0 1 lightning – WO 32 0,15 10 455,00 0,32 0 1 Table 2. Lightning strikes on structures. Statistics for 2008–2012 [5]. Causes: W – buildings with protection, WO – building without protection. protective system can be damaged to such an extent that it may not be able to provide protection against a subsequent lightning strike. If the owner or the op- erator of the building is not aware of the lightning strike, appropriate measures may not be taken. The Czech Hydrometeorological Institute records the times and the localities in which storms have oc- curred, for the purposes of insurance companies and claimants. However, the system does not provide ev- idence of a direct lightning strike on a building - it only provides evidence of lightning discharges in the locality. In our proposed system, each conductor is equipped with a wireless sensor, which records the event of a lighting strike. This data is subsequently used to check the effectiveness of the catchment sys- tem and to indicate where improvements are needed. 2. Lightning and the catchment system In the last five years, systems have appeared in in- dustrial applications that can monitor the passage of the lightning discharge through the conductor when a building is struck. These systems are based on the principle of electromagnetic induction, or they work with non-electrical phenomena such as polarized light signals. However, these systems indicate the light- ning strike only through a mechanical dial mounted directly on the conductor. As a part of our project, a wireless sensor module was prepared that provides online information about the state of the lightning current that is passing through. 3. Monitored building The proposed solution was developed by implement- ing a wireless sensor into a device used commercially for making a statistical record of lightning strikes on lightning conductors. Most devices used for monitor- ing systems struck by lightning are passive devices. After the critical current passes (mostly 2–100 kA) they can detect the event by increasing the mechan- ical counter by one unit. The speed with which this change is evaluated depends on the operator or on the building. By contrast, our proposed system works online, and immediately after the building has been struck it provides information on the passage of the current through the conductor. The monitored building is 5 × 3 × 4 m in size, and is situated in the Šumava region in the Czech Republic. According to the isokeraunic map [6], it is located in an area with an average frequency of 30–35 thunder- 879 Jan Mikeš, Ondrej Kreibich, Jan Neužil Acta Polytechnica Figure 1. Isokeraunic map of the Czech Republic. storm days per year (see Figure 1). Number of days with thunderstorms per year The advantages of the proposed solution are that instant information is obtained, and a rapid response can be made. The building can be disconnected from the networks, an engineer can be sent to make checks, and other actions can be taken to stabilize the struc- ture. When information is received, an integral part of the response is to predict that there may be a fire, which can often arise as a direct result of a lightning strike. However, there is often a delay before a fire breaks out, and the time interval can be used to take measures to minimize its impact. 4. Description of the proposed solution We present a modular solution that can be inte- grated into commercially-available instruments for registering lightning strikes. This paper describes the methodology for online transmission of information about lightning strikes, proposes a technological pro- cess for processing and evaluating the information, and describes the practical verification of a prototype. 5. Proposed system The proposed system for monitoring the passage of a lightning current through a collection conductor is based on the following conditions: • The device installation shall not affect the func- tionality of the building. • The equipment must be easy to install on new and existing buildings. • The device shall not significantly increase the bud- get for the construction of the lightning protection. • The device must provide long-term maintenance- free operation between inspections, and should ide- ally be completely maintenance-free. • The electronic part of the equipment should be pro- tected from the effects of shock. Figure 2. Concept of a sensor node [8]. Figure 3. Mesh multi-hop routing [8]. Under these conditions, wireless transmission was the only option. At the time when the system was im- plemented, an appropriate Wireless Sensor Network (WSN) technology was available. WSN is a net- work of wirelessly interconnected sensors that mon- itor the surrounding physical phenomena (light, hu- midity, temperature, etc.). Wireless sensors transmit measured data to each other, or are able to prepro- cess the data when it is transferred through networks to the so-called sink node. The sink node, also called the gateway node, transmits the data to the control unit (PC), where it is processed and analyzed. On the basis of this information, action is taken and/or information about the status of the monitored envi- ronment is displayed or transferred [7]. The sensor node is the basic unit of the Wireless Sensor Network. The sensor node generally consists of a sensor, a computer, a power supply, and a radio module (see Figure 2). The whole WSN system, i.e. computing perfor- mance, node performance and transmission protocols is expected to offer maximum energy saving and high flexibility. The node uses various levels of “sleep” when the performance of CPU, memory and the peripherals is controlled according to current needs (scanning parameters, data processing, communica- tion, inactivity, etc.). These networks can consist of just a few nodes, though there is no theoretical limit to the quantities. The network can operate with the well-known star topology as the basic arrangement, but the biggest benefit of WSN is that it forms mesh type networks using multi-hop routing, see Figure 3. For monitoring purposes, we used the Crossbow Iris development kit, which already supports mesh net- working technology thanks to the MoteWorks tech- nology. The properties of this series are summarized in Table 3 [9]. To capture the event when a discharge has oc- curred, we use the commercially available Dehn and Söhne lightning counter, enriched by the Iris node. The selected WSN technology ensures reliable data 880 vol. 53 no. 6/2013 A Lightning Conductor Monitoring System Electro – mechanical counter (original equipment) Electro – mechanical micro relay Latch circuit (original equipment) WSN module IRIS (MCU +radio + battery) Solar cell Toroid C on du ct or Figure 4. Lightning sensor node block diagram. Processor performance Processor Atmel ATMega 1281 Speed 8 MHz Program flash memory 128 kB Serial Flash 512 kB RAM 8 kB ADC 10 bit, 8 ch., 0–3 V input Operating system TinyOS 1.0 RF transceiver Frequency band 2.4 GHz ISM band, pro- grammable in 1 MHz steps Transmit data rate 250 kb/s Outdoor range > 300 m Indoor range > 50 m Table 3. Iris development kit features. transmission for periods of several years. When on battery power, the power supply battery needs to be replaced every few years. To enhance the lifetime of the system, we enriched the battery power system by a solar cell energy harvesting system, which operated reliably throughout the experiment. The sensing element of the sensor node is a toroidal coil with wound threads, in which the voltage is in- duced during the passage of the lightning current. In our application, we connected the input of the me- chanical counter to the micro relay. The micro re- lay serves primarily as a galvanic isolation element against voltage surges in the secondary circuit of the current sensing coil. The electronic equipment is therefore quite simple. It is basically a reference switch connected to the input of a simple microcon- troller and a radio module. The block circuit diagram is shown in Figure 4. The gateway is from the Iris set. It is used to con- nect with a PC via the USB. As the system is de- signed to be maintenance-free, we chose the power of the central node of the 230 V network (backup adapter). The digital output of the Iris gateway was applied to the digital input to the alarm with the GSM module (already installed in the house). The topology of the entire system is presented in Figure 5. 6. System Features The deep sleep mode of MCU in the sensor node con- sumes 8 µA, while in transmit mode the current is almost 17 mA. Thus the concept is based on the deep sleep mode while waiting for an event. The event is a lightning discharge. A discharge activates the re- lay connected to a +3 V backup battery (CR2030). This voltage wakes up the node. After waking up, the node sends an “event message”. The central node has radio communication continually powered- on, and when the message arrives it activates the GSM alarm input. Features of the wireless system: • nodes are inserted into the respective measurement points for the lightning conductor, • selected communication of the mesh type for guar- anteed transfer of discharge information, • the electronics of the measuring node is stored in- side a lightning counter, galvanically separated us- ing an electromechanical relay • the central node is connected to the GSM gateway of the house alarm • the power supply is provided by a photovoltaic cell and the backup battery 7. Economic balance sheet of the proposed system The components used in the test are relatively ex- pensive, but the topology of the system is relatively inexpensive. Today, such a system could be based on nodes available in a WSN network. After that, the balance sheet would be as follows: 881 Jan Mikeš, Ondrej Kreibich, Jan Neužil Acta Polytechnica NODE 1 DISTRIBUTION BOARD GSM ALARM OR A BUILDING BUS WSN GATEWAY NODE 2 NODE 3 NODE 4 Figure 5. Monitoring system topology. Figure 6. Lightning counter sensor node. • The sensing part (coil and circuit switching relays) < USD 5 • Complete WSN node < USD 10 • Gateway (Ethernet, USB or GSM) < USD 20 • Mechanical Parts < USD 10 The total cost of the system is around USD 70. How- ever the customer solution would be even cheaper (less than USD 50). 8. Summary The system described above was implemented in the lightning conductor of a family house in the Šumava region in the Czech Republic, and for a period of one year the events were recorded and transmitted to the central unit. In the assembled module, the key pa- rameters, mainly related to battery life, were verified. The authors suggest possible future possible exten- sion with precise wireless monitoring of the grounding system itself, detecting the amount of current passing through the conductor. The WSN technology enables sensing of commonly measured physical phenomena. This paper has shown that high-quality lightning pro- tection, especially with reference to disruption due to mechanical damage, is feasible. References [1] Hasse, P., Wiesinger, J., Zischank, W., Handbuch für Blitzschutz und Erdung. PFLAUM 2006. [2] Kutáč, J., Meravý, J., Ochrana před bleskem a přepětím z pohledu soudních znalců. Praha, Trenčín: SPBI, 2010. ISBN 978-80-7385-081-4. [3] Kutáč, J., Rozbor mimořádných událostí způsobených údery blesku v roce 2012. Seminar of UNIE SOUDNÍCH ZNALCU, 2012, ISBN 978-80-260-3382-0. [4] International Standard IEC 62305-3. Edition 2.0, 2010-12. Protection against lightning. Part 3: Physical damage to structures and life hazard. p. 151, Table E.2. [5] Fire and Rescue Service of the Czech Republic, http://www.hzscr.cz/ [6] http://mve.energetika.cz [7] Yick, J., Mukherjee, B., Ghosal, D., Wireless sensor network survey. Computer Networks, vol. 52, no. 12, pp. 2292–2330, Aug. 2008. [8] Neužil, J., Šmíd, R., Kreibich, O., Distributed Classification in Wireless Sensor Networks for Machine Condition Monitoring In: The Seventh International Conference on Condition Monitoring and Machinery Failure Prevention Technologies. Dublin: MFPT + BINDT, 2010, ISBN 9781901892338. [9] XMesh User’s Manual. [s.l.]: Crossbow Technology, 2007. 882 http://www.hzscr.cz/ http://mve.energetika.cz Acta Polytechnica 53(6):878–882, 2013 1 Introduction 2 Lightning and the catchment system 3 Monitored building 4 Description of the proposed solution 5 Proposed system 6 System Features 7 Economic balance sheet of the proposed system 8 Summary References