Large Steam Turbine Overspeed Trip Mitigation in Large Olefins Plans

Steam turbine overspeed events in large olefins plants can happen from a sudden loss of load in the driven equipment or instantaneous loss of coupled inertia as a result of complete coupling failure. This overspeed event occurs as load is rapidly depleted and steam is still being supplied to the rotor system. The largest contributor to steam turbine overspeed is entrapped steam and this paper will offer suggestions for OEM and Customer collaboration of steam turbine design with special consideration for ancillary components and supporting system parameters. Alternative means of initiating a trip event such as rate of acceleration and rotor-to-rotor angular monitoring will be offered as alternatives to traditional trip set points as a function of rated speed. 

In this paper, we will present findings regarding the most important considerations in the design, engineering and implementation of electronic overspeed trip systems, demonstrated through models and first-principles simulation to maximize system responsiveness, reliability, and availability.