Risk assessment of power system secondary devices for power grid operation

Abstract

Information and communication technology are the key issues of smart grid. Secondary devices, such as substation automation systems, relay protection systems, and EMS, play an important role in modern power system. A breakdown of secondary devices may result in a failure of power grid, even a large scale blackout. So it needs to evaluate risks of secondary devices for power grid operation. Up to now, risk assessments for primary devices are studied deeply, and a relatively complete theoretical system and analysis of assessment methods are formed. However, there is little research of the impact on power grid when secondary devices fail to work. The major work of this paper is to discuss the impact of a secondary device failure on power grid operation At first, the failure mechanism of secondary devices is studied. The failure of secondary devices is a problem of probability. The average working time between two adjacent faults, which is so called the mean time between failures (MTBF) is used wildly in information industry to evaluate the failure of information devices. From the point of statistics, regardless of the failure distribution patterns, when the running time of information devices is equal to the average working time, 50% to 60% of total number for certain devices will fail to work. Secondly the risk levels of the power grid after the function failures of different secondary devices are defined, such as relay protection devices, metering devices are corresponding to different risk levels of power grid. And furthermore, a complex secondary device is modeled into several logical layers, and dependencies between functions are mapped into series and parallel relations which is easy to calculate the power grid risk probability value of a single component or system-level secondary devices failure. The secondary devices of high risk can be identified by considering the running time and risk value. It is helpful to maintain secondary devices and reduce the risk of power grid.