## 1 Introduction
### Reliability  
Reliability describes the ability of a power system to supply electricity to all connected consumers in accordance with acceptable standards and quantities needed [6]. The reliability of an electrical system is characterized by two main aspects.  
Adequacy is a measure of the ability of a bulk power system to supply the aggregate electric power and energy requirements of the customers within component ratings and voltage limits, taking into account scheduled and unscheduled outages of system components and the operating constraints imposed by operations [7].  
Security is the measure of how an electric power system can withstand sudden disturbances such as electric short circuits or unanticipated loss of system components [7].  
The power system security assessment is used to determine whether the network is adequately protected against potential contingencies. Generally, system security assessment can be divided into two main classes, i.e., static and dynamic security. In the former case, the response of the electric power system to unforeseeable events in the steady state is analyzed. A static safety study examines the significance of over voltages and/or under voltages in busbars (or nodes) and the overload extent of power transmission lines and transformers. If, in the event of unforeseen events, the voltage values of all buses do not exceed a predetermined standard value and no transmission line or transformer is overloaded, then the electrical network is considered to be statically safe. In addition, the security analysis of the power system can be performed in the working (on-line) and non-working (off-line) state. The first package is used in the operation phase of the power system, and its results determine preventive and corrective power system/network management policies, while the second package is used during the power system's planning phase, which also includes future operating modes. The aforementioned classification is shown in Figure 1. For more detailed information on system security assessment, refer to reference [8].  
The purpose of off-line static safety assessment is to predict future flows in power transmission lines and voltages in busbars after unforeseen events/failures (contingencies).  
Figure 1: Classification of power system security assessment problems [2].  
Though this topic is extensively addressed in the scientific literature, it still remains an active research field, because the identification of severe operation modes enables the prevention of possible systemic accidents. A comprehensive review of static security is given in reference [9], which examines the methods and techniques used in this field in more detail.  
The purpose of our proposed ranking is to move the evaluation of the static security from long-term planning to shorter time windows. However, the problem remains the same--long simulation/evaluation time. It would take a tremendous amount of time to study all the possible/real scenarios of operation modes and the question is whether it is necessary to explore everything. Varying conditions in electricity systems (volatility of generation, load variation) make long-term security simulations difficult or even pointless. It is probably more sensible to focus on the daily or hourly operating modes of the system.