Lightning Performance on OverHead Lines
Lightning is a primary cause of service disruptions in overhead power lines, a challenge that has persisted since the early days of electrical power systems. The ability of these lines to resist and lessen the effects of lightning strikes is a vital component of power system reliability and functionality.
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Due to their elevated position and the extensive distances they span, overhead lines are especially susceptible to lightning. The term "lightning performance" refers to their capacity to endure lightning strikes and the effectiveness of measures to mitigate such impacts. A crucial measure of this performance is the frequency of outages per 100 km of line per year.
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Lightning-induced outages not only disrupt service but also incur significant financial costs for utilities, grid operators, and consumers, including equipment damage, contractual penalties, and the expense of momentary power losses.
In numerous regions globally, lightning accounts for more than half of all electrical outages, underscoring the profound influence of this atmospheric phenomenon on power system stability. Particularly in areas prone to frequent thunderstorms, the resilience of these lines against lightning is critical for reducing service interruptions and maintaining uninterrupted electricity delivery.
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The composition of the lines, their construction, design, and the geographic and climatic conditions they are exposed to greatly affect their susceptibility to lightning. Sophisticated modeling and forecasting tools are instrumental in gauging lightning strike occurrences and in the planning of more robust infrastructures.
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Process review of lightning outages mitigation
Due
Diligence
Lightning Induced Outages​
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Financial Damages
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Penalties from clients
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Costs of Momentary Outages
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Grid instability / Continuity of Service
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Intensive use of circuit breaker
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Potential risks for equipment
Investigation Analysis Audit Review
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Classification of Lightning-Induced Outages
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Determination of Ground Flash Density (GFD)
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Insulation coordination study/Lightning Withstand Levels
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Grounding Conditions: Reliable Measurements of Tower Footing Resistance and Soil Resistivity
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Verification Shielding angle & Verification shield wires/OHGW
Reduction
Elimination
Support Decision
Mitigation method
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Action plan / Project Execution
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Procurement Process & Logistics to site
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Training of linemen, operators and management for proper handling, assembling, installation, commissioning, and maintenance
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Live line installation and/or scheduled outages: Reliability, Safety & Efficiency as established processes
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Proactivity to monitor efficiency and detect failures (asset management and maintenance team)
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​Develop a long-term strategy to encompasses various parameters (e.g. Standardize LSA Application)
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Collaboration with Industry Experts (professionals experienced in best practices and the latest technologies)
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Carrying out dedicated lightning simulations to determine most cost-effective solutions (e.g. Optimal LSA Placement)
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Reliability and Preventive Maintenance. Maximize service life, minimize failures, ensure optimal LSA performance)
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Accurately define product specifications & Streamline the procurement process for effective vendor selection
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Develop an adequate program to control manufacturing processes, QA/QC activities and
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On-site training to ensure proper installation/maintenance
Facilitate
Integration
Implement Strategy as corrective measure
User Planning Integration
Due Diligence Process to evaluate feasability
The process of evaluating the lightning performance of an overhead line begins with a comprehensive due
diligence process. Undertaking this process is essential, as it enables utilities and system operators to really understanding the situation, the weaknesses, and consequently identify cost-effective solutions to mitigate lightning outages. The financial consequences of lightning-induced outages include direct financial damages, penalties from clients, costs of momentary outages, grid instability, and intensive use of circuit breakers.
The due diligence process involves several key steps:
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Identification of lightning-induced outages versus other types of outages. Retroactively or very proactively.
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Determination of Ground Flash Density (GFD) based on real-world data. Ideally using reliable Lightning Location System (LLS) networks.
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Verification of insulation coordination studies & insulator strings lightning withstand levels.
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Appropriate measurements of grounding conditions involving tower footing resistances and soil resistivity.
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Assessment of grounding electrodes and counterpoises' condition, if applicable.
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Verification of shielding angle & Inspection of shield wires/overhead ground wires (OHGW).
By conducting these steps, utilities and system operators can gather essential data and gain a better understanding of the lightning performance of their lines. This information enables them to make informed decisions about cost-effective solutions for mitigating lightning outages. A decision matrix can be employed to help evaluate the situation and prioritize a list of options, taking into account factors such as data availability, accuracy, and existing beliefs. This due diligence process is crucial for developing an effective strategy to optimize LSA investments for instance and ensure grid stability.
Latest status of research and continuous development
Lightning continues to be a leading cause of outages in transmission lines, despite being a subject of extensive study since the dawn of power transmission. Over the years, numerous strategies have been devised to assist transmission line designers in enhancing lightning performance. Ongoing research and development in this area are crucial for deepening our understanding of lightning phenomena and bolstering protective measures, which will result in more resilient and dependable power systems.
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Nowadays, many countries have access to intricate details on lightning activity thanks to advancements in lightning location systems (LLS). These systems have evolved steadily, exhibiting improvements in detection efficiency, location accuracy, classification precision, and the capability to estimate lightning peak currents.
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Recent research has shed light on the lightning attachment process to structures, enabling more accurate predictions of lightning strikes on lines and informing the strategic placement of lightning shielding and conductors. This knowledge is critical in reducing direct lightning strikes to phase conductors. Moreover, video recordings of lightning strikes on overhead lines and towers indicate that conventional shielding calculation methods, such as the Electro-Geometric Method (EGM), might not always predict stroke attraction accurately, particularly when upward leaders are influential in the attachment process, as seen with tall structures and Extra-High and Ultra-High Voltage conductors.
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Furthermore, advanced computational techniques like the Method of Moments (MoM) and Finite-Difference Time Domain (FDTD) are increasingly used to compute electromagnetic transients in electrical power networks. These Numerical Electromagnetic Analysis (NEA) methods, based on the numerical resolution of Maxwell's equations, enable more precise simulations of lightning responses in structures with non-uniform characteristics, such as transmission towers and ground electrodes. Insights from these sophisticated techniques contribute to the development of enhanced high-frequency models for ground electrodes and tall transmission line structures, which complement the more common and computationally manageable circuit-based methods found in various EMT program implementations.
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Lastly, the enhanced computational capabilities of modern personal computers, compared to those from the 1990s, allow for more complex modeling of lightning interactions with transmission line structures. This increased processing power is essential, especially when assessing the efficacy of line arresters in improving the lightning performance of transmission lines.
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Sources : This set of two CIGRE Technical Brochures (063 version 2021 + 839) apply present knowledge about the various aspects of lightning flashes, including the striking process, the discharge parameters, and the generation of overvoltages, together with the response of transmission line, develop a set of practical engineering procedures for estimating the lightning performance of a line with a reasonable degree of confidence.
