Research On The Methodology Of Risk Assessment Of The Power Secondary System Based On Functional Decomposition

Currently, the power system is experiencing rapid development. The power primary system (PMS) and the power secondary system (PSS) are becoming increasingly closer. The PSS has greatly improved the efficiency of the electricity production, however, it has also brought many uncertainties into the PMS. The safe and reliable operation of the PSS is now becoming an urgent problem in the power system.The risk assessment of the PSS contains two parts:the failure probability of the system and the severity of the consequences caused by the system failure. In this paper, a method for the risk assessment of the PSS based on functional decomposition is present. Firstly, the Function-Based Model (FBM) is proposed to decompose the PSS into functions. Then, the function reliability models are constructed to calculate the function failure probability. Secondly, security risk index (SRI) and operation risk index (ORI) are well defined to measure the severity of the consequences caused by the PSS failures. Finally, two examples are applied to verify the feasibility and applicability of the method.1. Information model of the PSS based on functional decomposition. The FBM is proposed to decompose the PSS into functions, and the function tree of the system and the function maps of the functions can be constructed after that.2. Failure probability analysis of the functions. Methods which can be used for reliability modeling of the functions are introduced, and the reliability block diagram method (RBDM) is used to establish the function reliability models. Then, the failure probability of the functions with different structures and different redundancy are analyzed.3. Consequences assessment of the function failures. SRI and ORI are well defined to measure the severity of the consequences which are caused by the of the function failures. SRI can reflect the severity of the consequences that the security requirements of the functions are not meet. The loss of load probability (LOLP) and expected energy not supplied (EENS) are used as ORI.4. Case study. The risk assessment method is applied to the risk assessment of the T1-1substation automation system and the control system of the improved RBTS system to verify the feasibility and applicability of the method.