Algorithm of calculation and forecasting of functional safety indicators of railway power supply systems

Acknowledgement: the authors express their personal gratitude to Prof. Igor B. Shubinsky, Doctor of Engineering, for his recommendations regarding the choice of the theoretical background that provided the foundation for the practical research, as well as hisadvice and valuable observations that contributed to this paper.

Abstract. Aim. Uninterrupted transportation process is ensured by the highly dependable and safe power supply system of railway transport. In addition, the railway power supply system provides power to external consumers. A risk-oriented approach to railway transportation management requires an infrastructure risk management and safety system. The main purpose of risk management in this area is to improve the dependability and safety of railway infrastructure facilities [1, 2]. Additionally, given the growing numbers of intelligent information systems, as well as automated railway transportation management systems, the task of ensuring functional safety becomes very important. In most cases this problem is solved by introducing redundancy that is understood as an exceeding complexity of the system structure compared to the minimal values required for the performance of the specified task [3]. The simplest way of ensuring redundancy is by creating backup capabilities, particularly standby duplication within the system of functional units and components. In order to evaluate the safety of the railway transportation power supply systems it is required to calculate the functional safety indicators of their components and system as a whole taking into account the factor of redundancy. This approach will enable the optimal redundancy architectures and ensure compliance with the assigned level of general system safety. That requires taking into consideration the complex structure of the evaluated facilities: presence of diagnostics systems, right-side failures, wrong-side failures, as well as their random nature. The paper aims to develop an applied algorithm of calculation and prediction of functional safety indicators using the example of railway power supply systems that can be used in both manual and automated calculation.

Methods. The power supply system evaluated for functional safety indicators is, from the functional point of view, a sequence of function implementations, while the failures of its components are random and some of them cause hazardous events. In this case, system analysis commonly involves Markovian and semi-Markovian methods, as well as graph methods. The advantage of these methods consists in the capability to evaluate the functional safety indicators of complex systems that go into many states, which is also typical for railway power supply systems.

Result. This paper examines the application of graph semiMarkovian methods for calculation of stationary and non-stationary functional safety indicators for components of power supply systems taking into account redundancy and right-side failures. This algorithm allows calculating safety indicators using the example of power supply systems and includes a set of incremental actions aimed at constructing the state graph, calculation of the initial and intermediate graph factors. An example is provided of calculation of the functional safety indicators of a graph of a traction substation power transformer. 

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