Optimum performance of protection ieds at oos in power system

Protective equipment's in high voltage substations should be providing fast, reliable localizes faults and selectivity. But, some abnormal condition in power system such as out of step (OOS) condition which mechanical power for the generator not equalized with electrical power for the load which is not a real fault but protection equipment’s will consider this condition is a fault. This situation will cause the loss of synchronism between areas within the power system or between interconnected systems that's will lead to blackout for the national grid. This paper will study the out of step condition, philosophy of protection relay device and how to overcome this condition by optimal method to avoid the false operation for distance function by Out of Step Blocking (OSB) to improve stability of power system.