What are the six major protection systems of a steam turbine?
3 Answers
OPC overspeed protection, electrical overspeed protection, mechanical overspeed protection, emergency trip device, reset test valve assembly, and steam turbine trip system are the six major protection systems of a steam turbine. A steam turbine, also known as a steam turbine engine, is a rotary steam power device. High-temperature and high-pressure steam passes through fixed nozzles to become accelerated airflow, which is then directed onto the blades, causing the rotor equipped with blade rows to rotate while performing external work. Steam turbines are the main equipment in modern thermal power plants and are also used in metallurgical industries, chemical industries, and marine power systems. Electrical overspeed protection: To ensure high reliability of the steam turbine overspeed protection, an independent two-out-of-three signal system is adopted. The system performs periodic tests regularly. The overspeed protection system features fast response and high reliability and safety. Mechanical overspeed: Composed of an emergency trip device, emergency trip mechanism, high-pressure trip assembly, and emergency trip linkage. The action speed is 110%-111% of the rated speed (3300～3330r/min). When the speed reaches the set value of the emergency trip device, the flywheel (or flyweight) of the emergency trip device is ejected, striking the latch of the emergency trip mechanism to release it. Through the emergency trip linkage, the emergency trip valve in the high-pressure trip assembly is activated, cutting off the high-pressure safety oil supply and releasing the high-pressure safety oil, quickly closing all steam inlet valves and tripping the unit. Emergency trip device: A protection device used to prevent severe overspeed of the steam turbine, also known as an emergency governor or overspeed governor. The emergency trip device is one of the important overspeed protection devices. Reset test valve assembly: In the tripped state, upon the operator's command, the reset solenoid valve 1YV of the reset test valve assembly is energized, introducing lubricating oil into the piston side chamber of the emergency trip mechanism. The piston moves up to the top dead center, resetting the latch of the emergency trip mechanism through the emergency trip linkage. Steam turbine trip system: The steam turbine trip system is a dual-channel system connecting electronic protection, overspeed protection systems, and trip solenoid valves. All steam turbine trip commands, including those from the overspeed protection system, electronic protection system, generator protection, and trip buttons, generate shutdown signals that actuate the trip solenoid valves through the steam turbine trip system to trip the unit.
The six major protection systems of steam turbines are primarily designed to prevent equipment damage and safety accidents. The first is overspeed protection, which monitors the rotational speed; if it exceeds the limit, the system will immediately shut down to prevent rotor burst. The second is low lubricating oil pressure protection, which alerts for oil replenishment or pauses operation when oil pressure is insufficient to avoid bearing burnout. The third is low vacuum protection; if the condenser vacuum drops, indicating steam cannot be discharged, it triggers protection to prevent overheating. The fourth is axial displacement protection, which automatically intervenes if the rotor moves excessively forward or backward, causing friction. The fifth is differential expansion protection, addressing inconsistencies in thermal expansion to prevent component deformation or cracking. The sixth is bearing vibration protection, which alarms and shuts down for maintenance when vibrations are excessive. These systems are implemented via sensors and controllers and are widely used in power plants or chemical plants to ensure stable and reliable operation. Regular calibration and cleaning are necessary to reduce failure rates.
The six key functions in the steam turbine protection system are absolutely critical—never underestimate them. Overspeed control is the primary safety line, triggering an emergency stop if RPM exceeds limits. Low lubricating oil pressure is unacceptable as it can seize bearings and destroy the machine. Insufficient vacuum must be strictly managed to prevent steam blockage and internal burnout. Excessive rotor displacement triggers alignment protection to correct positioning issues. Differential expansion protection prevents crack risks from uneven thermal expansion. Vibration protection shuts down the unit for inspection when oscillations exceed thresholds. Having witnessed these in plants firsthand, neglecting protection often leads to explosions or costly shutdowns—monthly oil pressure and sensor checks are vital preventive measures. Scheduled maintenance programs enhance system durability and minimize unexpected failures.
