The turbine trip signal initiates fast closure of all steam inlet valves (e.g., turbine stop valves – TSVs) to block steam flow through the turbine. In a turbine trip event, a malfunction of a turbine or reactor system causes the turbine to trip off the line by abruptly stopping the steam flow to the turbine.
Every steam turbine is also provided with emergency governors who come into action under specific conditions. In general, an unplanned or emergency shutdown of a turbine is known as a “turbine trip”. The turbine trip signal initiates fast closure of all steam inlet valves (e.g., turbine stop valves – TSVs) to block steam flow through the turbine.
The turbine trip event is a standard postulated transient, which must be analyzed in the Safety Analysis Report (SAR) for nuclear power plants.
In a turbine trip event, a malfunction of a turbine or reactor system causes the turbine to trip off the line by abruptly stopping the steam flow to the turbine. The common causes for a turbine trip are, for example:
the speed of the turbine shaft increases beyond specific value (e.g., 110%) – turbine overspeed
balancing of the turbine is disturbed or due to high vibrations
failure of the lubrication system
low vacuum in the condenser
manual emergency turbine trip
Following a turbine trip, the reactor is usually tripped directly from a signal derived from the system. On the other hand, the reactor protection system initiates a turbine trip signal whenever a reactor trip occurs. Since there remains energy in the nuclear steam supply system (NSSS), the automatic turbine bypass system will accommodate the excess steam generation.
Schema of a steam turbine of a typical 3000MWth PWR.
References:
Reactor Physics and Thermal Hydraulics:
J. R. Lamarsh, Introduction to Nuclear Reactor Theory, 2nd ed., Addison-Wesley, Reading, MA (1983).
J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.
W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
Todreas Neil E., Kazimi Mujid S. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, Second Edition. CRC Press; 2 edition, 2012, ISBN: 978-0415802871
Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Plant Systems. Springer; 2015, ISBN: 978-3-319-13419-2
Moran Michal J., Shapiro Howard N. Fundamentals of Engineering Thermodynamics, Fifth Edition, John Wiley & Sons, 2006, ISBN: 978-0-470-03037-0
Kleinstreuer C. Modern Fluid Dynamics. Springer, 2010, ISBN 978-1-4020-8670-0.
U.S. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume 1, 2, and 3. June 1992.
U.S. NRC. NUREG-0800, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition
