The Emergency Trip System (ETS) is an important guarantee for the safe operation of steam turbines, and the following is a detailed explanation of the steam turbine ETS and its protection content:
First, overview of ETS
ETS is a real-time monitoring system for steam turbine operating parameters and status, and when an abnormal situation is detected, it can quickly cut off the steam intake of the steam turbine and make the steam turbine stop in an emergency to protect the steam turbine equipment from damage and avoid major accidents. It is mainly composed of sensors, logic control units, actuators and other parts. The sensor is responsible for collecting various operating parameters of the steam turbine, the logic control unit analyzes and judges these parameters, and the actuator realizes the emergency trip operation according to the instructions of the logic control unit.
Second, the content of the ETS protection
1. Overspeed protection: During the operation of the steam turbine, due to sudden changes in load, failure of the speed regulation system, etc., the speed may exceed the rated speed. When the speed reaches 109% - 111% of the rated speed, the ETS will trigger the overspeed protection to quickly close the main valve and adjust the valve to prevent serious accidents such as flying due to overspeed.
2. Lubricating oil pressure protection: Lubricating oil plays a role in lubrication and cooling of rotating parts such as bearings of steam turbines. When the lubricating oil pressure drops to a certain value, it will affect the normal operation of the bearing, and even lead to failures such as tile burning. Normally, when the lubricating oil pressure drops to about 80% of the normal oil pressure, the ETS will send an alarm signal to remind the operator to take measures; When the oil pressure continues to drop to a lower value, such as 40% - 50% of the normal oil pressure, the ETS triggers trip protection and stops the turbine.
3. EH Low Oil Pressure Protection: The EH oil (anti-fuel) system provides power to the regulating system of the steam turbine. When the EH oil pressure is low to a certain extent, it will affect the normal operation of the adjustment valve, resulting in the reduction of the adjustment performance of the steam turbine. Generally, when the EH oil pressure drops to about 85% lower than the normal oil pressure, the ETS will trigger the protection to quickly close the main valve and adjust the valve to ensure the safety of the steam turbine.
4. Large axial displacement protection: During the operation of the steam turbine rotor, due to the action of steam force, temperature difference and other factors, axial displacement will occur. When the axial displacement exceeds the specified allowable value, the dynamic and static parts of the steam turbine will rub and damage the equipment. Normally, when the axial displacement reaches a positive or negative limit value, such as ±0.8mm - ±1.0mm, the ETS will act immediately to cause the turbine to stop in an emergency.
5. Large expansion difference protection: When the steam turbine is starting, stopping and running under variable working conditions, due to the different thermal expansion rates of the rotor and cylinder, the expansion difference will occur. When the expansion difference exceeds the allowable range, it will cause the dynamic and static clearance of the steam turbine to change, which may cause frictional collision of dynamic and static parts. Generally speaking, when the positive expansion difference reaches 1.5mm - 2.0mm and the negative expansion difference reaches -1.0mm - -1.5mm, the ETS will trigger the protection and stop the steam turbine operation.
6. Bearing vibration protection: Steam turbine bearing vibration is one of the important indicators reflecting the operating status of the steam turbine. Excessive vibration can affect the life of the bearing and may even cause damage to the shafting. When the vibration amplitude of the bearing reaches a certain value, such as the peak value of shaft vibration exceeding 75μm - 100μm, the ETS will decide whether to trigger trip protection according to the duration and severity of the vibration.
7. High temperature protection of thrust pad: The function of the thrust pad is to bear the axial thrust of the steam turbine rotor and ensure the axial position of the rotor. When the temperature of the thrust pad is too high, it will lead to the wear and burning of the thrust pad, which will affect the safe operation of the steam turbine. Generally, when the thrust pad temperature reaches 95°C - 100°C, the ETS will send out an alarm signal; when the temperature continues to rise to 110°C - 120°C, the ETS triggers protection and shuts down the turbine.
8. High temperature protection of support pads: Support pads provide radial support for the turbine rotor, and if its temperature is too high, it can affect the lubrication and cooling effect of the bearing. Normally, when the support pad temperature reaches 80°C - 85°C, the ETS will send out an alarm; when the temperature exceeds 95°C - 100°C, the ETS will perform a trip operation.
9. Low condenser vacuum protection: Condenser vacuum is critical to the efficiency and safe operation of the steam turbine. If the vacuum is too low, the exhaust pressure of the steam turbine will increase, resulting in an increase in the axial thrust of the steam turbine, and at the same time, the exhaust temperature will also increase, which will affect the safety of the final blades of the steam turbine. When the condenser vacuum drops to a certain value, such as -87kPa - -90kPa, the ETS triggers protection to shut down the turbine.
10. Generator fault protection: When the generator experiences a serious failure, such as a short circuit in the stator winding or grounding of the rotor winding, it may affect the operational safety of the steam turbine. At this point, the generator's protection device will send a signal to the ETS, which will immediately trip the steam turbine upon receiving the signal to prevent the fault from escalating and to protect the generator and steam turbine equipment.
11. Manual emergency trip protection: To enable a quick stop in an emergency, the ETS has a manual emergency trip button. When the operator identifies a serious abnormal situation with the steam turbine, such as a fire or significant leakage on site, they can directly press the manual emergency trip button to prompt the ETS to act immediately, cutting off the steam inlet to the steam turbine and achieving an emergency shutdown.
12. DEH power loss protection: The digital electro-hydraulic regulation system (DEH) is a crucial control system for the steam turbine; if the DEH system loses power, it will be unable to effectively control the steam intake of the steam turbine. At this time, the ETS detects the DEH loss signal, triggers protection, closes the main valve, and adjusts the valve to prevent the turbine from losing control.
