Asian Journal of Basic Science & Research (AJBSR) Volume 2, Issue 1, Pages 35-49, January-March 2020 Concept and Application of Lightning Arrester for 11kV Electric Power Systems Protection Research Article Received: 22 November 2019 Accepted: 27 December 2019 Published: 23 January 2020 1 Uche C. Ogbuefi , Cajetan M. Abstract: The phenomenon of lightning is an exciting natural incident. However, its rate of 2 3 Nwosu & Cosmas U. Ogbuka occurrence can be as critical as it is electrifying. The magnitude of energy contained in lightning 1,2,3 Department of Electrical Engineering, strikes is very high and can be destructive. In order to prevent electric power equipment from University of Nigeria, Nsukka, Enugu State, Nigeria. lightning, protection schemes like the use of lightning rods, ground wires and surge diverters are put in place to curtail its effects on electric equipment. This device is used for the protection of Corresponding Author Author Email: substations equipment against high travelling waves, by arresting the abnormal high voltage spike [email protected] to the general mass of the earth devoid of affecting the continuity of supply. In this paper, a detailed design of surge diverter or lightning arrester for protection of electric power system is presented. 1. INTRODUCTION SOLIDWORKS software was utilized in this study to access the performance analysis and Lightning is unpredictable and it application of an 11kV valve-type surge diverter modelled after the IEEE lightning arrester model. Different lightning arrester models are presented. By Slight variation to the IEEE model, a 92% is the most destructive of all reduction in the lightning-induced voltage was recorded. Thus, the modified model can be applied elements associated with to the protection of 11kV power systems for more reliable and improved supply of power to thunderstorms. It causes damage customers. to many objects and systems such as electronic circuits, overhead and underground electric power and communication systems, buildings, boats, and aircraft and launch vehicles in flight. It is the most frequent cause of over voltages on distribution systems [1, 2]. The voltage of a lightning strike may start at hundreds of millions of volts between the cloud and earth. Although these values do not reach the earth, millions of volts can be delivered to the buildings, trees or distribution lines struck [3]. Lightning is a direct transient current that has been recorded to be up to 260,000 amperes and last for duration of up to 200 microseconds making it very hard to study [4]. According to [5], lightning strikes and thunderstorms during rainfall are very likely to occur frequently and hence protection of equipment Nomenclature especially transformers, that can be affected by their occurrence 푅1 = Filter resistance 푋퐿 = Filter inductive reactance should be treated with utmost priority [6]. 1 휇퐻 = Micro-Henry, sub unit of Inductance Ω = Ohm, unit of Resistance Lightning as a physical phenomenon, occurs when the clouds 퐿1 = Filter inductance 퐶 = Terminal-to-terminal Capacitance of Arrester acquire charge or become polarized, thus creating electric fields 푅0 = Stabilizing Resistance Inductance associated with the magnetic 퐿 = of considerable strength between the cloud and adjacent masses 0 field in the immediate vicinity of the arrester LA= Lightning Arrester such as earth and other clouds [5]. However, it takes a very MO= Metal Oxide conductive atmosphere below/about 50 km owing to the MCOV= Maximum Continuous Operating Voltage 푉푠 = System line-to-line voltage presence of ions created by both cosmic rays and the natural 퐶푒 = Coefficient of Earthing Maximum system voltage radioactivity for lightning to be triggered [7]. Studies carried out 푉푚푎푥 = 푉푃 = Phase Voltage by Mowete and Adelabu [8] indicates that in the early times, the ZnO = Zinc Oxide destructive effects of lightning strikes were limited mainly to high voltage (HV) power supply lines, but with the Copyright@2020 AJBSR www.ajbsr.net Page | 35 Asian Journal of Basic Science & Research (AJBSR) Volume 2, Issue 1, Pages 35-49, January-March 2020 advent of mobile telephony services, information technology infrastructure concern expanded to include the increase in equipment fatalities occasioned by the absence of lightning protective systems. The choice of protection depends on the criticality of the load, relative size of the transformer compared to the total system load and potential safety concerns. Percentage differential protection is the most widely used scheme for the protection of transformers rated 10 MVA and above [9, 10]. Lightning arresters are essential devices of serious importance in areas prone to lightning strikes hazards like losses due to equipment damage [11, 12]. They are used to prevent the disastrous effects of lightning on buildings, power and communication systems, and equipment in general. As a result, the reliability of an electric power system is greatly affected by lightning strikes to such effects as line design, the frequency of lightning flashes, the magnitude of the lightning over voltages and the failure statistics of power system components as a major cause of power outages worldwide [13, 14, 15]. This is because, lightning damages power system equipment and many times renders them inoperable thereby making the system very unreliable. For instance, in 2003 United States, Canada and Europe suffered a series of blackouts, attributed majorly to lightning strikes leaving more than 60 million people without electricity [15, 16]. In addition, according to [17] a direct lightning strike on a power line or an induced voltage from a nearby strike may lead to line „„flashover‟‟ or failure of arresters, transformers, insulators, or other line hardware. Flashovers or equipment failure can result in an out-of-service line, which is a more technical term for an „„outage” [18, 19]. Different types of lightning arresters exist and they differ in material construction. They operate almost on the principle to provide low resistance path for the surges to the general mass of the earth. Their selection depends on the factors like the material makeup, current, voltage ratings they can withstand, their reliability mostly and others follow. There are the rod arrester, multi gap, metal oxide, horn gap, expulsive type, valve type lightning arresters. The issue with the rod lightning arrester is that once the spark occur, it may continue for some time even at low voltage. This is taken care of by the use of current limiting reactor in series with the rod. The presentation of the design of a valve type lightning arrester modelled after the IEEE model is the main concern of this work. Valve type of lightning arresters incorporate non-linear resistor. As the magnitude of lightning current/voltage is very high, the non-linear elements will offer a very low resistance to then passage of the surge which will rapidly go to the general mass of the earth instead of being sent back over the line. The non-linear resistors take up high resistance to stop the flow of current as the surge is over. 2. MODELS OF LIGHTNING DIVERTER A number of good models have been proposed to describe the arrester behaviour for different kinds of stress [20]. There are mainly three lightning arrester models namely as presented in [21]: i) IEEE model, ii) Pinceti model, and iii) Fernandez-Diaz model Fig. 1(a) shows the model recommended by IEEE. It uses the non-linear V-I characteristic which is obtained by means of two non-linear resistors, represented by A0 and Al and separated by an R-L filter. For slow surges, the filter impedance i.e. 1|| 1 is extremely low and A0 and AI are practically connected in parallel, with R = 1 and L Copyright@2020 AJBSR www.ajbsr.net Page | 36 Asian Journal of Basic Science & Research (AJBSR) Volume 2, Issue 1, Pages 35-49, January-March 2020 = 1 [20]. The corresponding inductive reactance, 1is obtained by computing 1 accordingly. A0 and A1 are non-linear resistors (varistors) whose values have already been defined experimentally by the committee of IEEE W.G. 3.4.11 [3]. Figure 1 and Table 1 summarize the results of the experiments. They are represented by the MOV blocks in Figure 8. Figure 1: V-I characteristics of nonlinear resistors A0 and A1. Source: [3, 4] Using the details provided in Table 1, the non-linear characteristics Table 1: V-I characteristics for A0 and A1. of A and A can be obtained for any value of discharge current, I [kA] V [p.u] 0 1 bearing in mind that they are to be calculated to match the residual A0 A1 voltages for the lightning discharge currents of the protection 0.1 0.963 0.769 V-I-characteristic provided by the manufacturer, which is the 1 1.05 0.85 Crompton Greaves ZLA2007 Lightning arrester in this case (See 2 1.088 0.894 Figure 7 and Table 2 [6]. Obtaining the values of A0 and A1 by hand 4 1.125 0.925 would be quite laborious and laden with error. The use of the 6 1.138 0.938 ATPDraw software however, simplifies this as when a nonlinear 8 1.169 0.956 branch element like a metal oxide arrester (whose resistance is 10 1.188 0.969 typified by A0 or A1) with MOV Type-92 component is specified in 12 1.206 0.975 the ATPDraw software. ATPDraw accepts the current/voltage (V-I) 14 1.231 0.988 characteristic and performs an exponential fitting in the log-log 16 1.25 0.994 domain to produce the required ATP data format [7]. The Pinceti 18 1.281 1 model shown in Figure 2(b) was proposed by Pinceti and 20 1.313 1.006 Giannettoni in 1999. It is based on the IEEE model with some minor differences [21] A0 and A1 are the non-linear resistors, L1, the filter inductance and R0 the stabilizing resistance are used to avoid numerical oscillations [22, 23].