2014 International Conference on Lightning Protection (ICLP), Shanghai, China Energy incident from lightning induced voltages on low voltage power installation due to cloud to cloud flashes in Sri Lanka N Sapumanage, S Nanayakkara, S Jayalal, M Fernando Department of Physics, University of Colombo Colombo 00300, Sri Lanka nilanthas@pucsl.gov.lk V Cooray Uppsala University Uppsala, Sweden vernon.cooray@angstrom.uu.se Abstract— In modern world electronic and electrical appliances are used in abundance and such devices are constantly plugged onto the low voltage power installations (LVPI). Thus, savvy on amount of energies incident by induced voltages on overhead utility lines is important in protecting such equipment. In this paper, preliminary observation of incident energy by induced overvoltage signals on the interface between overhead utility lines and LVPI by cloud flashes is presented. Recorded waveforms were first segregated into cloud to ground (CG) and cloud to cloud (CC), then all recorded CC discharges categorized under three distinct wave shapes unipolar, bipolar and pulse- burst as described previously by [3] and [4]. Observed highest energy corresponding to the unipolar, bipolar and pulse-burst pulses were 0.56 J, 1.51 J and 7.30 J against the peak to peak voltages of 405 V, 662 V and 1056 V with pulse durations of 33.64 μs, 95.00 μs and 222.69 μs respectively. It was further observed that overall mean values of incident energies for unipolar and bipolar were 0.25 J and 0.69 J respectively, compared to 1.46 J observed for pulse-burst pulses. Analysis revealed that profile of the induced voltages and the pulse duration play a major role in deciding the magnitude of the incident energy. It was observed that common mode (CM) induced voltages with pulse-bursts type signatures inherently having longer pulse durations and hence contains comparatively higher energy than lenient pulses. Further, it was observed that in many occasions, there were multiple induced voltages appeared in the 200 ms window. Therefore, the outcome of the study lead to valid conclusions that CC discharges could incident sufficiently high energies to harm sensitive electronics and great attention should be made to confront with CC discharges with special attention to pulse burst type induced voltages. Keywords- CC, flashes, CM induced voltage, LVPI I. INTRODUCTION During past few decades lightening related equipment damages have been gone up unprecedentedly [8]. This particular study intended to surface severity levels of CC discharges in terms of energy incident by the CM induced voltage on LVPI. Since CC discharges are much higher in number comparatively to CG discharges, if CC threat levels are found significant, then CC would be the most significant contributor towards damages. Thus to adhere towards much precious and sustainable mitigation options, one need to understand the threat levels and effects of CC lightning activities to a great depth. A few studies have been done in understanding the energy of ground flash induced surges on utility lines [5], [6] and [7]. However, no study has been done on the same for cloud flashes as per our knowledge. Silfverskiӧld et al (1999) [1] and Galvan et al [2] have revealed that not only the return stroke, but also the preliminary breakdown in ground flashes and cloud flashes could have potential for incident sufficient energy to drive sensitive electronic devices towards total or partial failures. Most of modern day sophisticated equipment contains several microprocessors for various purposes. Usually, they have very low immunity against surges due to their inherent compacted nature in construction. According to Keith Brashear (ILD Technologies, LLC San Antonio, TX) [7] microprocessors are subject to weakening damage from reverse electrical energy as little as one micro joules. Integrated circuits are subject to damage from with as little as 10 μJ. Inbuilt surge immunity ranges from no protection (zero) to up to about 12 J for commercially available electronic devices to electrical equipment such as switch mode power supplies, etc., Silfverskiӧld et al. (1999) [1], have differentiated the degree of threat levels that could produce by a single pulse or pulse trains and managed to established that many energy absorbing devices were damaged by multiple overvoltage pulses, although they were not damaged by a single overvoltage pulse. They further elaborated that even though protective devices can withstand a single pulse by absorbing incident energy by the semiconductor devices (MOVs), they are more prone to degradation and thermal damage if they have to encounter with a sequence of over voltage pulses. The wave shape of the CM induced voltage waveform at the interface of LVPI may have different shapes owing to various factors. Silfverskiӧld et al. , [1] had explained that the wave shapes depend on the source of the fields, propagation paths, geometrical and electrical characteristics of the