Source: Thermal Power Plant Technology Alliance
1. Overview:
ETS is the abbreviation for Steam Turbine Critical Trip System. The turbine critical trip system is used to monitor certain parameters of the steam turbine, and when these parameters exceed its operating limit, the system closes all turbine steam inlet valves and causes an emergency shutdown. In order to ensure the safe operation of the turbine, these parameters are monitored:
In any of the following protection actions, the four AST solenoid valves all lose power, directly drain the AST safety oil pressure and OPC oil pressure, and quickly close the high and medium pressure main valves and adjust the valves to achieve shutdown
- DEH超速:汽机转速>3300rpm(信号来自DEH)
- TSI超速:汽机转速>3300rpm(信号来自TSI)
- Large axial displacement: the shaft displacement of the steam turbine reaches ±1.0mm (zero position is at the thrust centerline)
- Low vacuum: the vacuum of the turbine condenser is less than 70 kPa (absolute pressure is greater than 28.0 kPa)
- Low lubricating oil pressure: The lubricating oil pressure of the steam engine is lower than 0.06MPa
- Low EH oil pressure: The EH oil pressure of the steam engine is less than 8.0MPa
- Large shaft vibration: any shaft vibration of the steam turbine is greater than 250um, and any other shaft vibration is greater than 150um, and the protection action is delayed for 2s
- High thrust pad temperature: the temperature of any thrust bearing exceeds 107°C (valid before grid connection, automatically exited after grid connection)
- Turbine Pressure Ratio Protection: Regulating Pressure/High Discharge Pressure< 1.734 (Effective above 90MW)
- Sudden steam temperature drop: superheated steam temperature/reheat steam temperature drop by 50°C/10 minutes
- High exhaust temperature: 427°C higher exhaust temperature of high-pressure cylinder (two measurement points execution logic with)
- Generator protection: generator tripping steam turbine (internal cold water cut-off protection action generator)
- Boiler protection: boiler MFT jump steam turbine
- DEH loses power
- Manual shutdown (simultaneous press of two buttons)
The system applies the dual-channel concept, arranged as an "or-and" gate channel mode, which allows the in-line test, and the device still plays a protective role during the test, and each contact of the other three low-signal signals is connected to the online monitoring state, so as to ensure the reliability of the system.
The trip signal sent by the ETS system is sent to the following systems and the corresponding equipment is activated:
Steam engine EHA system: After receiving the ETS trip signal, the EHA system will act the main valve and the valve to trip the solenoid valve (the solenoid valve coil will be de-energized when the reverse logic is used; the solenoid valve coil will be energized when the positive logic is used), the trip oil pressure will be discharged, and the main valve and valve adjustment valve will be quickly closed.
2. Working principle:
The system cabinet is placed in the electronic room, and two sets of PLCs are used to run in parallel, that is, it is defined as machine A and machine B, and machine A and B are redundantly controlled. When the operating machine fails, the other machine immediately switches to the running state.
The touch screen is provided with a trip "first out" signal memory light, and each group of signals can give a "first out" memory signal, that is, the first coming trip signal indicator light flashes bright, and the other trip signal indicator lights are always on, and after manual reset, the trip signal disappears. Generally, the trip solenoid valve will adopt the logic of taking two out of four. The four trip solenoid valves are connected in series and parallel, i.e. AST1 and AST3 in parallel, AST2 and AST4 in parallel, and then in series. Trips only when there is an action in AST1 and AST3 and one action in AST2 and AST4,
Working principle of trip block:
The trip block is installed on the right side of the front box, there are a total of 6 solenoid valves on the block, 2 OPC solenoid valves are 110VDC, normally closed solenoid valves, OPC solenoid valves are controlled by DEH, 4 AST solenoid valves are controlled by ETS, the power supply of solenoid valves is 110VDC, normally open valves. Under normal circumstances, the AST solenoid valve is a normally charged structure, and the two 110VDC power supplies are taken from the electrical DC screen. One of the power supplies controls AST1 and AST3 solenoid valves, and the other power supply controls AST2 and AST4 solenoid valves. There are various power detection relays in the cabinet to detect the working condition of the power supply.
The connection of the trip block solenoid valve is as follows:
Four ASTs are connected in series and in parallel, that is, No. 1 and No. 3 solenoid valves are connected in parallel, No. 2 and No. 4 solenoid valves are connected in parallel, and No. 1, 3 and 2 and 4 are connected in series. As illustrated.
When two parallel AST solenoid valves 1 and 3 are opened at the same time or one of them, although the AST oil controlled by the open solenoid valve is connected with the AST oil drain port on the solenoid valve, because the 2 and 4 solenoid valves connected in series are not opened, the AST oil and the non-pressure return oil circuit are not connected, and will not have a big impact on the AST oil pressure. ASP oil pressure high alarm will be generated, but the unit is working normally.
In the same way, when two parallel AST solenoid valves 2 and 4 are opened at the same time or one of them, although the AST oil controlled by the open solenoid valve is connected with the AST oil drain port on the solenoid valve, the AST oil that is discharged at this time is the AST oil flowing through the throttle hole, and the AST oil that is discharged is limited, because the 1 and 3 solenoid valves connected in series with it are not opened, it will not have a big impact on the AST oil pressure. ASP oil pressure low alarm will be generated, and the unit will work normally.
And when the solenoid valve of 1, 3 or 1, 3 and 2, 4 or 2 and 4 is opened at the same time, the AST oil and the non-pressure return oil circuit are connected, the AST oil will be quickly depressurized, causing the OPC to be depressurized at the same time, and the main valve and the adjusting valve are closed.
Because the whole trip block adopts the principle of "double channel", when any solenoid valve in a channel is opened, the channel will be tripped; but the steam turbine inlet valve can not be closed, only when both channels are tripped, the steam turbine steam inlet valve can be closed, and the trip effect is played, so its reliability is greatly improved, and the "misoperation" and "rejection" can be effectively prevented.
Working principle of trip test block:
The system has a total of 4 test blocks, EH oil test block, LBO lubricating oil test block and LV1 and LV2 vacuum test blocks. The principle is the same for each block. The schematic diagram is as follows:
Each test block is arranged as a double channel. J1 and J2 are throttle holes, F, F1 and F2 are manual valves, S1 and S2 are solenoid valves, B1 and B2 are pressure gauges, and K1, K2, K3 and K4 are pressure switches.
The function of the throttle hole is to isolate the two ways, so that they do not interfere with each other during the test. The test can be done manually in situ or remotely in the main control room via the test button.
When using the remote test, there is a lock on the circuit to ensure that the two roads will not be tested at the same time, and when one is tested, the other road has a protection function.
When using the local manual valve test, it cannot be done at the same time, otherwise it will cause false tripping. This is especially the case when testing manually. Under normal circumstances, the pressure oil is sent to the pressure switch and the indication table B1 and B2 through the throttle hole, the indicator table will indicate the normal oil pressure, once the oil pressure is reduced, as long as each of the 4 pressure switches on both sides has a switch action, it will cause a trip.
During the test, turn on F1 or S1, and when the indicator on B1 is that it will slowly descend to the set value, K1 and K3 will act. During the ETS remote online test, the indicator light on the corresponding test plate is on, indicating that a certain road on the corresponding trip control valve is being tested. Because the trip valve is arranged into a double channel, so only one test will not produce a trip signal, if the measured parameters really reach the shutdown value at this time, the pressure switch on the test block will be all action, the two signals through the "and" effect, the trip signal will be generated, and the unit will be stopped through the trip control block. Therefore, the test block can be tested online and does not affect the protection function of the unit.
The power supply for the test block solenoid valve is 220VAC. After the test is completed, it is necessary to pay attention to whether the gauge pressure returns to the normal value, otherwise it is not allowed to test another way, so as not to cause false jumping.
When the equipment is working normally, the first trip signal is green, and when there is a signal tripping, the light of the corresponding signal will continue to flash (from green to red to green). The subsequent alarm signal can only be solid (flat red), which is the function of having the first out. When the ETS trips, the turbine shutdown light will stay on (from green to red).
Test Lights:
When you press this button, you can see that all the alarm lights will turn red, this function is mainly to check whether the alarm signal and PLC communication are normal.
In-line testing features:
There is a switch on the top of the plate, and when it is rotated to the in-line test position, the in-line test light will be lit to indicate that the following tests can be performed. The buttons of the two channels are interlocked, and ASP1 and ASP2 also participate in the interlocking relationship of the two channels, so as to prevent the two channels from being tested at the same time and causing false hopping stops.
When doing the online test, it should be noted that after the channel that has just been tested returns to normal, another test can be performed. This is done by observing the status of the ASP1 and ASP2 LEDs. Otherwise, the test of the other channel cannot be done, because the channels are interlocked
ETS Power Monitoring Light:
When the ETS is working normally, the power monitoring light on the disk is solid red, and the light is green during shutdown and fault conditions.
When the key switch under the disc is rotated to the running position of the unit, the overspeed suppression light and the re-line test light are not lit, and the corresponding functions do not work.
Conservation projects
1. EH oil pressure low protection: EH oil pressure low signal is the local EH oil pressure switch signal, a total of four channels, the four signals are directly introduced into the ETS system, using dual-channel connection mode (63/LP-1, 63/LP-3 and 63/LP-2, 63/LP-4), each channel has at least one switch action as a shutdown signal, that is, 63/LP-1 or 63/LP-3 action and 63/LP-2 or 63/LP-4 action. The setting value of the pressure switch is 8MPa.
2. Steam turbine lubricating oil pressure low protection: The steam turbine lubricating oil pressure low signal is the local pressure switch signal, a total of four channels. These four signals are directly introduced into the ETS system, using a two-channel connection mode, and each channel has at least one switching action as a shutdown signal. The pressure switch has a setting value of 0.06 MPa.
3. Low vacuum of condenser: The vacuum low signal of the condenser is the local vacuum switch signal, a total of eight channels, each low-pressure cylinder corresponds to four channels, and any low-pressure cylinder vacuum low protection action will send out a protection action. The setting value of the vacuum switch is 28KPa (absolute pressure);
4. Large axial displacement of steam turbine: the large axial displacement signal of steam turbine is taken from TSI, a total of four axial displacement sensors are installed on the west side of the front box thrust pad, axial displacement 1 and axial displacement 2 are installed on the west side of the measuring disk, axial displacement 3 and axial displacement 4 are installed on the east side of the measuring disk, and its zero point position is the center of the thrust pad, when the two axial displacements installed in the same direction reach -1.0 mm or +When 1.0mm, that is, both side 1 and 3 or 2 and 4 are action, the axial displacement detection instrument sends an axial displacement large contact signal to the ETS system to realize axial displacement protection.
5. TSI overspeed: TSI overspeed signal is taken from TSI, TSI system detects the three-way speed signal, the three-way speed probe is installed at the 88-tooth speed measuring plate at the crank, when any one speed signal reaches 3300RPM, the speed detection instrument will send an electric overspeed contact signal, and the three-way signal is sent to the ETS system through the three-to-two logic to achieve electric overspeed protection.
6. Large shaft vibration: The turbine generator set has a total of nine bearings, #1-#8轴瓦分别设置X方向和Y方向轴振传感器, a total of 16 measuring points, any shaft vibration is greater than 250чm, and any other shaft vibration is greater than 150чm, protection action. In this protection, the axis vibration of another point is greater than 150чm in DCS, and a DO point is output, and the shaft vibration is greater than 250чm at any point in ETS and TSI and the post-protection action.
7. Large relative displacement/expansion: The so-called expansion difference is the thermal expansion difference between the turbine cylinder block and the rotor. The signal is taken from the TSI system, two probes are installed on the high-pressure cylinder expansion, and the output is a composite output of the two probes, and the low-pressure cylinder expansion is an LVDT sensor. In the original design, the expansion difference of the high-pressure cylinder of the steam turbine was +11.1 mm in the positive direction and –4.7 mm in the negative direction, and the expansion difference of the low-pressure cylinder of the steam turbine was +23.5 mm in the positive direction and –1.52 mm in the negative direction. Any of these four items will cause the turbine to operate with differential expansion. At present, the protection decision of "large expansion difference between high and low cylinders" of steam turbines has been cancelled, and it has been changed to a first-level alarm to remind the operator to stop the machine manually.
8. DEH power loss: DEH interface power supply and control power supply have a total of four protections, when any power supply protection action, the DEH power loss protection action will be sent to ETS.
9. Manual shutdown: The manual shutdown button is installed on the console of the control room, and the two buttons are pressed at the same time to issue manual shutdown protection to ETS.
10. DEH110% overspeed: DEH judges the three-way speed signal, implements the three-way pick-up, and sends out a protective action signal when the speed is greater than 3300RPM, and stops at ETS.
11. Generator protection action: When the generator protection action, send out the protection action signal and stop at ETS.
Among them, the generator water cut-off protection is realized by the cold water inlet and outlet differential voltage low switch in the internal chilled water station with a three-to-two delay of 30S, the logic is done in the SC4 controller, and the DO output is hardwired to the electrical through the ETS cabinet.
12. Furnace MFT: When the boiler MFT protection action, send out the protection action signal and stop the ETS.
13. High thrust bearing temperature: 4 temperature elements are installed on the thrust pad, thrust bearing temperature (positive) P4, thrust bearing temperature (positive) P2, thrust bearing temperature (pay) G4, thrust bearing temperature (pay) G2, when the temperature of any temperature element exceeds 107 °C, the steam turbine "high bearing temperature" protection decides to introduce the metal temperature of each support bearing [with anti-jump cut], either support bearing metal temperature or thrust bearing temperature high steam homogeneous engine trips, and the protection is effective before grid connection, and automatically exits after grid connection.
14. The steam turbine pressure ratio is low: the signal of the regulating pressure 1, 2 and 3 is high selection, and the high discharge pressure 1 and 2 are high selection, when the regulating pressure / high discharge pressure is < 1.734, the steam turbine pressure ratio low protection action is issued.
15. High exhaust temperature and high jump machine: the protection value of "high exhaust temperature and high temperature" of the steam turbine is revised to 427 °C, and the anti-jump removal function is added, and the protection action is taken when the high-pressure exhaust steam temperature is 1 and 2 are high.
16. Sudden drop in superheated steam temperature: the temperature of the main steam drops by 50 degrees in 10 minutes, and a high exhaust temperature and high protection action signal is sent to ETS.
17. Sudden drop in reheat steam temperature: The temperature of reheat steam drops by 50 degrees in 10 minutes, and a high exhaust temperature and high protection action signal is sent to ETS.