To prevent the generating station stoppage on account of frequency variations, certain protection devices like over frequency, under frequency, and rate of change of frequency (ROCOF) relay are used to shed the load to bring the supply frequency within the rated frequency range. In this condition, the supply frequency decreases, and the df/dt relay protects the power system by load shedding. The protection relay is a very important device for the protection of the electrical system. For example. While the information and guidance given in this document is believed to be correct, no liability shall be accepted for any loss or damage caused by any error or omission, whether such error or omission is the result of negligence or any other cause. Any and all such liability is disclaimed.