Protection Against Abnormal System Frequency

This chapter presents the need for abnormal frequency protection and describes protective measures that are commonly used. It provides more detailed examinations to the generators/power trains used in most traditional power generation, namely steam‐turbine driven generators and their power train. The chapter considers the effects of sustained operation of a generator that is in an emergency island, created as a result of some system disturbance, which produces the condition that either over‐or underfrequency exists in the island. It also considers some features of steam turbine design that are important from the standpoint of off‐normal frequency operation and specific turbine protection for over‐ and underfrequency operation. This discussion deals only with steam turbines since they are traditionally the most affected types. Turbine underfrequency protection is the last line of protection and its operation may lead to blackout of the underfrequency island.