ارزیابی قابلیت اطمینان در شبکه‌های توزیع سوخت شهری به روش گراف مسیر

Introduction
The fuel distribution network in the country has a vital role and is responsible for supplying the fuel chain from the refinery to the consumption stage at the refueling station. Due to the critical role of this network in providing the required fuel to vehicles, estimating the reliability and risk and the amount of unsupplied fuel in it is of particular importance. In this study, with the aim of evaluating the reliability of complex fuel distribution networks, a numerical model based on the route graph method in MATLAB software has been developed, and the fuel distribution network of Damavand city has been studied as a case study by the model. In this regard, first, the existing fuel stations in the city are identified and classified. While forming the general graph of the distribution network and naming its nodes, the communication lines between the stations are drawn according to common standards (supporting and adjacent stations), and the developed algorithm has calculated all the available routes from the source refinery to the destination sites. Finally, with the acquisition of the routes, the final assurance of fuel supply at the destination stations has been obtained. The results show that the fuel station "Velayat Abali " with 94% reliability has the minimum amount, and the fuel station "Besat" with 96% reliability has the maximum amount of reliability in the distribution network. Also, defining the configuration of supporting stations in the distribution network increases the reliability of the system.
Introduction
Reliability modeling and evaluation in distribution networks, including energy, water, and fuel distribution, has progressed significantly in recent years. The statistics show that water and energy distribution networks have the largest share in the unsupplied energy of subscribers. For example, power distribution networks contribute to consumer blackouts, and water distribution networks make a significant contribution to customer water outages. Energy and fuel networks may suffer from performance and failure due to various external and internal factors. External factors mainly include earthquakes, avalanches, special weather conditions, etc., and internal factors, depending on the type of network, are due to failure of control systems, manpower error and limited useful life of equipment. Due to the importance of maintaining network performance in such situations at the desired level, in recent years, several methods have been proposed to evaluate the performance of complex networks that express network reliability in conditions of uncertainty (critical conditions). Since energy and fuel distribution networks are generally complex systems, it is appropriate to use the concept of network equivalent graphs to simplify them.
The primary purpose of this study is to introduce an algorithm to calculate the reliability of fuel distribution networks. Achieving this goal requires considering a range to generalize the proposed model and calculate the final reliability. In this regard, by considering the fuel distribution network in Damavand city as a case study, the final reliability of this network is calculated.
Materials and methods
Numerous methods have been developed to calculate system reliability, especially in cases where the system cannot be considered in series. The most prominent methods developed are: conditional probability method, cut method, tree diagram method, logic diagram method, connection matrix method, and path graph method. Due to the appropriate approach of the path graph method and its ability to be developed in the software platform, this method has been used in the present study. In this method, all the paths that connect the system input to its output are considered and the reliability of each path is calculated; In other words, the conditions leading to the successful operation of the system are determined. This method is based on the concept of connection set; A connection set is a non-duplicate path of components, the failure of each of which leads to the failure of the connection set, and if any of the sets are in place, the system will function properly. Each set has a parallel connection with the other sets and its members are in series.
Result
After determining the set of available routes developed by the algorithm and having the reliability of each fuel station, the overall reliability of the network is obtained according to Table 4.
 
Table 4. Calculation of the final reliability of the fuel distribution network in Damavand city




Selected route set


Reliability


Breakability


fuel not supplied (liters)




Routes leading to station number 5


0.940233


0.059776


2988.4




Routes leading to station number 6


0.955031


0.044969


1798.8




Routes leading to station number 7


0.958154


0.041846


1673.8




Routes leading to station number 8


0.961156


0.038844


1942.2




 
 
Discussion and Conclusion
 The summary of the results is as follows:

Regarding the reliability of the fuel supply chain of the fuel station of Abali province, with 94% reliability, it has the minimum value. It is the critical point of the distribution network.
Besat fuel station located on the south side of the central area with 96.1% reliability is the most reliable station in the fuel distribution network of Damavand city.

The use of support stations and two-way communication between adjacent stations in the fuel supply management method increases the system's reliability.