Out-of-step protection fundamentals and advancements

Power systems are subjected to a wide range of small or larger disturbances during operating conditions. Small changes in loading conditions occur continually. The power system must adjust to these changing conditions and continue to operate satisfactorily and within the desired bounds of voltage and frequency. The power system should be designed to survive larger types of disturbances, such as faults, loss of a large generator, or line switching. Certain system disturbances may cause loss of synchronism between a generator and the rest of the utility system, or between interconnected power systems of neighboring utilities. If such a loss of synchronism occurs, it is imperative that the generator or system areas operating asynchronously are separated immediately to avoid widespread outages and equipment damage. In this paper we describe the philosophy and application fundamentals of out-of-step protection in transmission systems. We also discuss recent enhancements in the design of out-of-step tripping and blocking protection functions that improve the security and reliability of the power system. In addition, we demonstrate the out-of-step phenomena and distance relay element behavior using EMTP and Matlab simulations.