An adaptive method for setting underfrequency load shedding relays

An adaptive scheme is proposed for determining the amount of load to be shed by underfrequency relays based on the observed initial slope of the frequency deviation. following the system separation. This initial slope contains all the information required to estimate that size of the step change in load caused by the system separation and to forecast the depth and even the approximate time of the maximum frequency dip. From this observation, the first step of load shedding can be set up adaptively, with additional steps to follow at prescribed intervals and amounts. The first step is considered the most important and is selected arbitrarily at one-half the static load shed target, with additional increments of about 0.1 per unit to be shed at 0.3 Hz increments until the dynamic load shed amount has been reached