As the second defense line for power grid security, the reliable operation of security and stability control device is critical to the safety of the power grid. Based on the hardware and software design principles of the security and stability control device and the on-site operation regulations, the various links related to device reliability are analyzed from three aspects of hardware principle, software principle and field operation. The fault tree model and the Markov state space model are established, from which the probability of device in normal operation, hidden fault and outage operation state are concluded. Further measures for improving reliability have been proposed for each link that affects the reliability of the device. Finally, taking the CSS-100BE device as an example, the effects of the reliability improvement measures were evaluated based on the field operation record and the test data of the laboratory for nearly 10 years.

security and stability control device； reliability； Markov； improvement measures