Power system designers and operators have been always looking for solutions to prevent the expansion of normal disturbances and also to prevent cascading outages in case of an emergency situation. Backup protections, most of the times, play an effective role in preventing small disturbances to spread all over the system. Changes in the operating point of the power systems affects the access area of the protection relays and this lead to inappropriate protection system functions, especially in backup relays. Due to the change of power transfer in the major tie lines after the outage of a faulted line, cascading trips counts as an important menace to the stability and security of power systems.The inherent delay of the existing backup relay protection systems along with the effects of fault resistance on pushing the observed fault out of the range of the main protection relay settings and the conventional backup protection relay could lead to expansion of the disturbances, cascading line outages and ultimately a blackout in the systems. The main purpose of this thesis is to investigate the drawbacks of the existing conventional backup relaying systems and using wide-area protection for obviating these drawbacks. The main structures and facilities necessary for implementation of wide-area backup relaying systems are introduced and as examples two wide-are backup protection relaying schemes are investigated and introduced in detail. One of these schemes works based on the measurement of the positive sequence of bus voltages and difference in line current angles and the other one works based on some expert algorithms which use the results of conventional protection schemes. The performance of these two schemes is compared with each other by simulation of different fault scenarios on the well-known 39 bus New England standard test system. Simulation results show that the proposed protection scheme has a good capacity for reducing wide-area disturbances system blackouts and can result in a more secure operation of power systems. Keywords: Wide-area measurement systems, Phasor measurement unit, Wide-area Backup protection systems, Cascading outage.