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Top1. Introduction
In India, the unavailability of power based on weather is a cause of outrage and bitter criticism from the public against the power utilities. For example, during the rainy season, the frequency of power failure and down time is high leading to protest against the Government and power utilities (Gauree, 2018; Saini, 2018; Sony & Mekoth, 2014, 2015). Among the other reasons of power failure, the weather is one of the most important factors affecting the reliability of power systems (Panteli, Pickering, Wilkinson, Dawson, & Mancarella, 2017; Zhou, Pahwa, & Yang, 2006). The supply chain model of the power system from Generation, Transmission, and Distribution has to work together to cater the reliable power to consumers (Pabla, 2012). The transmission and distribution lines are affected by weather-related failures. Analysis of transmission line is important because the failure of transmission lines will lead to the power outage of several distribution lines leading to blackouts (Sony Michael & Mariappan, 2012). The failure rates are dependent on the weather conditions around which the transmission line operates. Increased failure rates are reported in different types of weather condition (Wu, Gao, Tang, & Huang, 2016).
Not only the failure rates the downtime are also influenced by the weather conditions (Tavner et al., 2013). For an overhead transmission system, the weather environment can severely impact the performance of the transmission lines leading to the power utility's operational ability due to enhanced line failure and repair rates during bad weather periods (Billinton & Singh, 2006). Therefore, estimating reliability by utilities without incorporating weather conditions can be quite optimistic and erroneous. In addition, it may also affect planning and design decisions for maintenance activities for the power utilities, which will result in the financial loss (Fanucchi, Bessani, Camillo, London, & Maciel, 2016). By recognizing the impact of various weather contributions to the total system performance indices will help to pinpoint the situations, where investment may be provided for maximum reliability improvement. A transmission and distribution system usually consists of overhead lines, underground and combination of both (Pabla, 2012). In utilities like India, which is a developing country, the ratio of overhead transmission lines to underground transmission lines are very high (Saini, 2018). Hence, assessing the reliability of systems without incorporating, weather-related outages would lead to erroneous conclusions resulting in bad policy and maintenance strategies. In other words, for cash-starved utilities, incorporating weather-related outages will lead to optimum allocation of available resources. Another aspect to consider in a developing country is that the repair process is also dependent on weather (Sony Michael, Mariappan, & Kamat, 2011). Thus, failure rate and repair rate are a continuous function of weather conditions. It is difficult to describe failure rate and repair rate as a continuous function of weather-related failures. However, a set of discrete states could be used to describe the variable failure and repair rates. Previous researchers have used the concept of failure bunching to model storm related failures (Billinton & Singh, 2006; Gaver, Montmeat, & Patton, 1964). Markov models were used in the evaluation of transmission system availability if the rate of failure and repair followed exponential distribution (Michael et al., 2009).