Investigation of Lightning-Initiated Flashover Faults in Medium Voltage Overhead Lines - Modelling and Experimental Evaluation
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Journal Title
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School of Electrical Engineering |
Doctoral thesis (article-based)
| Defence date: 2016-05-23
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Author
Date
2016
Major/Subject
Mcode
Degree programme
Language
en
Pages
117 + app. 103
Series
Aalto University publication series DOCTORAL DISSERTATIONS, 70/2016
Abstract
Lightning can cause flashovers on Medium Voltage (MV) lines from both direct and nearby strikes. The work presented in this dissertation thoroughly investigates the characteristics of lightning-initiated flashover faults, expected overvoltage stress and the performance of different surge protection schemes to mitigate the lightning overvoltages. A full-scale experimental set-up is established to investigate the nature of lightning-initiated flashover faults in MV lines. The flashover voltage of the overhead line is determined by changing the type (metallic/wood) and the configuration (grounded/ungrounded) of the cross arm. On the other hand, the instant at which the flashover occurs is determined by the actual volt-time curve of the line insulation whereas the arcing phenomenon is represented by the dynamic arc model. A complete model of the experimental set-up is developed in Alternative Transients Program–Electromagnetic Transients Program (ATP-EMTP) and the experimental results have been reproduced with reasonable accuracy. The lightning performance of a typical MV unearthed network due to both first and subsequent direct strokes is also analyzed. The transient overvoltages at the MV terminals of distribution transformer are determined from ATP-EMTP simulations. Accordingly, the effectiveness of different lightning protection schemes based on of spark gaps and surge arresters is also assessed. The volt-time curves and the flashover probability distributions of different types of insulation gaps subjected to positive and negative standard and short tail impulse voltages were established. The study was further extended by testing the insulation gaps with combined AC and lightning impulse voltages. The experimental flashover probability distributions are then compared with those predicted by the modified Gaussian cumulative distribution function of the insulation flashover under combined voltages. A statistical method of insulation coordination based on probabilistic risk assessment is also introduced in this work to evaluate the lightning performance of MV lines. In this regard, the probabilistic model of insulation flashover is experimentally validated to predict the probability of single-phase, two-phase, and three-phase flashover of insulators. Accordingly, the effect of combined AC and lightning-induced overvoltages on the risk of flashovers above perfectly conducting and lossy ground is also investigated. Finally, the risk-based insulation coordination method is applied to determine the optimum insulation level and spacing between the consecutive surge arresters for the mitigation of lightning-induced overvoltages.Description
Supervising professor
Lehtonen, Matti, Prof., Aalto University, Department of Electrical Engineering and Automation, FinlandThesis advisor
Lehtonen, Matti, Prof., Aalto University, Department of Electrical Engineering and Automation, FinlandKeywords
lightning, insulator flashover, medium voltage line, arc, risk, transformer, surge arrester, shield wire, spark gap, ATP-EMTP.
Other note
Parts
- [Publication 1]: F. Mahmood and M. Lehtonen “Experimental Investigation of Lightning-Initiated Flashover Faults in Medium Voltage Lines,” International Conference on High Voltage Engineering and Applications (ICHVE’14), Poznan, Poland, Sept. 8-11, 2014
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[Publication 2]: F. Mahmood, N. I. Elkalashy and M. Lehtonen “Modelling of Flashover Arcs in Medium Voltage Networks Due to Direct Lightning Strikes,” International Journal of Electrical Power and Energy Systems (JEPE), vol. 65, 2015, pp. 59-69.
DOI: 10.1016/j.ijepes.2014.09.036 View at publisher
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[Publication 3]: F. Mahmood, M. E. M. Rizk and M. Lehtonen “Evaluation of Lightning Overvoltage Protection Schemes for Pole-Mounted Distribution Transformers,” International Review of Electrical Engineering (IREE), vol. 10, no. 5, Sep./Oct. 2015, pp. 616-624.
DOI: 10.15866/iree.v10i5.7266 View at publisher
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[Publication 4]: F. Mahmood, M. E. M. Rizk, N. A. Sabiha and M. Lehtonen “Flashover Probability Distribution and Volt-time Curves of Medium Voltage Overhead line Insulation under Combined AC and Lightning Impulse Voltages,” International Review of Electrical Engineering (IREE), vol. 10, no. 5, Sep./Oct. 2015, pp. 625-632.
DOI: 10.15866/iree.v10i5.7150 View at publisher
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[Publication 5]: F. Mahmood, N. A. Sabiha and M. Lehtonen “Probabilistic Risk Assessment of MV Insulator Flashover under Combined AC and Lightning-Induced Overvoltages,” IEEE Transactions on Power Delivery, vol. 30, no. 4, Aug. 2015, pp. 1880-1888.
DOI: 10.1109/TPWRD.2015.2388634 View at publisher
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[Publication 6]: F. Mahmood, N. A. Sabiha and M. Lehtonen “Effect of Combined AC and Lightning-Induced Overvoltages on the Risk of MV Insulator Flashovers above Lossy Ground” Electric Power Systems Research, vol. 127, 2015, pp. 101-108.
DOI: 10.1016/j.epsr.2015.05.016 View at publisher
- [Publication 7]: F. Mahmood, M. Humayun and M. Lehtonen “Risk-Based Design Methodology for the Selection of Insulation Level Against Lightning-Induced Overvoltages in Medium Voltage Lines,” 19th International symposium on High Voltage Engineering (ISH’15), Pilsen, Czech Republic, Aug. 23-28, 2015
- [Publication 8]: F. Mahmood, M. E. M. Rizk, N. I. Elkalashy and M. Lehtonen “Application of Risk-Based Insulation Coordination Method for the Protection of Medium Voltage Overhead Lines against AC and Lightning-Induced Superimposed Voltages,” submitted to Electric Power Systems Research, 2016
