On the Use of Dynamic Thermal-Line Ratings for Improving Operational Tripping Schemes

The increasing volume of renewable and intermittent generation that is being connected to power systems means that system operators need more advanced dynamic control tools to manage the increase in congestion and the resulting pressure on system constraints. The dynamic thermal-line rating (DTLR) is the thermal rating of a transmission line that is calculated in real time based on online measurements of the loading of the asset and local weather conditions. This dynamic rating will usually be greater than the static rating that is currently used, as the static rating is defined for the worst case scenario. Therefore, using the dynamic rating allows the thermal constraint on a line to be relaxed and the maximum loading increased. An operational tripping scheme (OTS) is a type of system integrity protection scheme that is used to relieve overloads on transmission lines during stressed system conditions by tripping preselected generation assets that are connected to the protected lines. An OTS is used to increase power flow on overhead lines, without building new assets or compromising security, but doing so results in potential generation constraints and higher system risk. This paper presents the novel integration of DTLRs into an existing OTS in order to improve its performance by reducing the likelihood of unnecessary generation tripping due to overly conservative line ratings. This novel OTS affords the system economic benefits, by avoiding unnecessary tripping, and improves system security by limiting the propagation of disturbed conditions and avoiding unnecessary tripping actions that could initiate dangerous cascading events that might lead to system blackouts. The new scheme is an example of a wide area monitoring, protection and control application.