Assessment and classification of line overload risk in power systems considering different types of severity functions

Power system security assessment based on the concept of risk is required in the current power environment. In risk based security assessment, the likelihood and severity of security violation are the two main factors that determine the security level of a power system. To evaluate likelihood of security violation, the probability technique based on Poisson probability distribution function is adopted. Severity function signifies the extent of security violation. Two types of severity functions, namely the continuous and percentage of violation severity functions are considered in this study. This paper presents the assessment of risk of line overload at various loading condition using a risk index. A risk classification technique is also proposed so as to provide a qualitative interpretation of the risk index value by classifying the risk as low, medium and high degree of risk. This paper presents the implementation of line overload security assessment on the IEEE 24 bus test system and practical interconnection power system so as to investigate the effect of severity functions on risk classification in risk assessment. Results are presented in terms of risk index curves.