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Network security risk assessment is an important means of acquiring and mastering the current and future state of network, which is of great significance to maintain the safe operation of the network. This paper presents an improved risk assessment method based on Markov game that has simply changed the past, in which the risk status of the network assets were classified into fixed categories. Depending on the game relationship between fixing vulnerabilities and threat attacking, this method has more detailed characterization of the network risk. Network attacks and vulnerabilities are sorted, which reduces the state space, making the scale of model input greatly reduced, improving the assessment of large-scale network efficiency. Simulation results demonstrate the feasibility and effectiveness of this method.

The circuit model of potential transformer (PT) is indispensable in accurately simulating the electromagnetic characteristic under the lightning overvoltage and very fast transient overvoltage in power systems. This paper utilizes a reduction algorithm for potential transformer based on revised minimum information loss method (RMIL). First, we measured a 10 kV single phase potential transformer using the Agilent 4395A network/spectrum/impedance analyzer. Second, we obtained the rational approximation of two-port circuit parameters by vector fitting (VF). At last, revised minimum information loss method is applied to reduction the state equation of circuit parameters. Comparisons between the reduced and original are given to illustrate the approximating performance of RMIL.