Turbine Overspeed Systems and Required Response Times

Turbine overspeed events lead to the most dangerous and costly of catastrophic turbine failures. Traditionally, overspeed protection systems were designed and provided by the original equipment manufacturers (OEMs)—few options were available either in terms of testing or modifying these systems. With new turbines, and with the retrofit of older systems, it is more common to see third party systems playing this critical protective role. However users often do not appreciate the overspeed protection system response time that is required to adequately protect their equipment. This tutorial will explain the basic components of a turbine trip system, and consider sources of variability in the response times of those components. Industry standards, API 612 (2005) and API 670 (2000), will be used to show how to calculate the required overspeed protection system response time. Users will walk out of this tutorial with a basic understanding of what comprises a steam turbine trip system, a greater appreciation of the affect of the system response time, and an understanding of how to verify that their system has the adequate response time to protect their turbines, plants, and personnel.