Aspects of power system protection in the post-restructuring era

Protection practices in the electric utility industry as it existed prior to re-structuring were designed to meet certain goals of sound engineering principles, as they were applied, primarily to component protection in vertically integrated electric utility systems. There has been a significant shift in emphasis from uncomplicated component protection to system protection to avoid or mitigate wide-area disturbances. It is not clear how the responsibilities for designing and maintaining the protection system will be divided between the transmission system owner and the ISO. Protection and control of generators will also impact the performance of the power system. The settings used in many protection systems that are designed to protect power apparatus will affect the ability of the transmission system to transfer power between two points on the network. The owners of the transmission system as well as the ISO should have an interest in knowing the limitations imposed by both the apparatus and the system protection, and the ability to change those settings if they do not meet their respective objectives. It is possible that the objectives of the two entities will be in conflict. The paper examines the existing protection philosophies, and their impact on these issues.