Reliability evaluation of composite generation and transmission sys-tems based on stratified and gradual importance sampling algorithm

Aiming at the low efficiency of Monte Carlo simulation in power system probability analysis. The paper will use layered important sampling technology in reliability evaluation. The system state space is divided into different levels of subspace according to the important degree and category of system components. It will calculate the optimal multipliers of failure probability in the different layers and optimize the important sampling function gradually. So the later algorithm will have more advantage .It avoids the degeneration phenomenon for conventional sampling in the higher reliability system. The paper compared the method of this paper whit other methods in IEEE-RTS79 and its modified system. The results show the method of this paper not only ensuring calculation accuracy but also improving the calculation speed and efficiency.