Graphical method for estimating impact of distance line protection into electric power system stability

Changes in regulations and the opening of the power markets are causing rapid changes in the way the power grid is operated. Large amounts of power are commonly shipped across a transmission system that was not designed for such transactions. Independently owned and operated generating units are being built in locations that may not be optimum for system stability and system needs. Power plant systems are being upgraded to get every possible megawatt out. The results of these upgrades often make the generating units more susceptible to instability. Power systems have experienced a number of large disturbances in the last ten years. All of these disturbances caused considerable loss of generation and loads. Typically, these disturbances happen when the power systems are heavily loaded and a number of multiple outages occur within a short period of time, causing power oscillations between neighboring utility systems, low network voltages, and consequent voltage instability or angular instability. This paper delivers a graphical method for estimating impact of out-of-step protection settings using study results from a dynamic simulations of an interconnected system. Short circuits faults are unavoidable in power system. These faults should be removed fast and affected part should be isolated quickly with a minimum of disturbance to the remaining system. To this purpose a reliable and fast acting protection system is essential. It will minimize the risk that a local occurrence is leading to a threat for the entire system. When a protection system is designed a compromise must be made between economy and performance, dependability and security, complexity and simplicity, speed and accuracy. In this paper the focus is on the optimal relay performance as seen from a system point of view. Two aspect of reliability are usually addressed in case of relay engineering, dependability being a measure or the relaying equipment’s ability to correctly clear a fault while security is a measure of the relaying equipment’s tendency not to trip incorrectly.