This study presents a new methodology for fault-induced line outage detection in the power transmission network. Pre-fault operating conditions and synchronised phasor measurements at all generator buses are used to accomplish this task. Initially, the proposed scheme divides the whole power system under study into different protection zones corresponding to generator bus (es). Furthermore, a new index termed as 'gain in momentum' (GIM) at each generator bus is used to identify the expected tripped region (ETR). This information helps in reducing the search space. Once the ETR is identified, online measured power flow of line connected to generator of ETR having maximum GIM is compared with the estimated post-outage power flow of the same line. The post-outage power flow is obtained using pre-outage line flow and line outage distribution factor. The aforementioned power flow comparison helps in identifying the tripped transmission line. The performance of the proposed scheme is validated on the IEEE-39 bus New England system and 246-bus North India Grid using the Power System Simulation for Engineering software. The test results indicate that the proposed scheme is highly effective in identifying the tripped line of a transmission system. © The Institution of Engineering and Technology.