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After the retrofit of the turbine speed control system, the accuracy of the speed control and load control has been greatly improved, which fully demonstrates the advantages of stable startup and high control accuracy. At the same time, some abnormal problems are exposed in the operation, in which the displacement sensor failure of the speed control valve is typical. Each main steam valve of the steam turbine is equipped with a displacement sensor, and each speed control valve is equipped with two displacement sensors. The system uses the sensor with high feedback value as the control object to adjust. The main valve remains fully open after the gate is closed, and no adjustment is performed. The displacement sensor only operates when the valve activity test is performed; the speed control valve frequently switches according to the requirements of the speed adjustment and the load control, and the displacement sensor also adjusts the door The switch does not stop, so it is easily damaged. When one sensor is damaged and it is removed, the other can work normally without affecting the load adjustment of the unit; if both are damaged, they must be replaced online to ensure the control of the door. The following is an analysis of some typical phenomena caused by faults in displacement sensors, and then find out the corresponding solutions.
Second, the phenomenon of failure and analysis 1. Phenomenon from the beginning of March 27, 2000, # 3 machine # 2 pressure repeated intermittent slight vibration in the door, the door control instruction is 110% and does not change, the feedback value in the 86 ~ 95mm Between the changes, the local adjustment of the door and the EH oil line shook violently. In severe cases, there has been a phenomenon that the connection plug of the displacement sensor signal line is dropped due to excessive vibration.
Reasons for splitting: Displacement sensor failure of the door is adjusted, causing a feedback signal to be distorted; the servo valve command control line is loosened, causing the DEH control command signal received by the servo valve to mutate.
Inspection and processing: When inspecting the servo valve command line, it is found that the wiring is loose and the shaking phenomenon disappears after fastening; when the displacement sensor is inspected, it is found that the feedback line plug is detached, and the shaking phenomenon disappears after re-installation and fastening, and later it is replaced with no plug. The integrated sensor avoids such failures.
2. Phenomenon 2 During the period from November 2000 to February 2001, the #6 machine #2 high-pressure control door repeatedly experienced intermittent violent shaking. Initially, the use of single, multi-valve switching and a small amount of load adjustment method can avoid the door swing, but this method is not lawless, still can not completely eliminate the phenomenon. The most serious shaking occurred on February 2, 2001 (at that time, the unit had 18 OMW operation), and caused the load to fluctuate significantly between 160 and 2OOMW, and the jitter of #2 high-voltage control gate reached 20%; after 15 minutes of stability, there was a drama. The column shakes, the load fluctuates between 130 to 19 OMW, and the #2 high-pressure swings between 50 to 100%. In the meantime, the #2 shaft vibration was abruptly changed from 116 μm to 160 μm, and the axial displacement was between -0.1 mm and -0.3 mm. Throughout the entire process, the #2 high-pressure tuning command has been 100%.
Analysis of reason: When #2 high-voltage control door shakes, the feedback signal of #1 displacement sensor has a sudden increase phenomenon, which causes the DEH command value (A value) of the VCC card to be much lower than the feedback value (P value) of the adjusted door after high selection, resulting in Reduced load caused by sudden opening of the door. After the sudden drop in load, another large high-pressure control door was opened under the effect of the power loop to maintain the target load, and thus a sudden increase in load occurred. In addition, the high-pressure control door overlap is set larger, # 1 and # 2 high-pressure control doors are not fully open at 18OMW, resulting in poor adjustment stability of the door, which also exacerbated the valve shake.
Treatment: Increase the frequency difference between two displacement sensors (from 5OHz to 100Hz), reduce the possibility of resonance of the two sensors; dismantle the #1 displacement sensor, and the shaking phenomenon disappears; change the overlap of the high-voltage control door, #1, #2 When the door is opened to 75%, the #3 door starts to open, and the #3 door is opened to 50% when the #4 door is opened.
3. Phenomenon III. On March 18, 2003, the load of Unit 2 was abruptly changed. The DEH screen showed that #2 high-pressure control door was fully opened, and the pressure after the door was adjusted decreased from 12.3 NPa to 9.2 MPa.
Analysis of the reasons: After analyzing the historical data, it can be seen that the LVDT1 feedback value suddenly increased at the time, which made the system think that #2 high-pressure control door opening is too large, thus issuing a close command. Since the LVDTl has been damaged and the door has been closed, the feedback value is still the maximum and the display is fully open. It can be seen that the load dump is due to the damage of the LVDT1.
Treatment: Since the LVDT2 has been damaged before this and the two sensors are malfunctioning, online replacement must be performed to ensure normal load control.
Third, the online replacement of the displacement sensor According to the replacement method provided by the supplier, must be fully open and close the door a number of times to adjust the zero and fullness of the valve control card (VCC card). Adopting this method will inevitably bring about abrupt changes in the load of the unit, which will seriously threaten the safe operation of the unit. In practice, through many tests, we have summed up a set of effective methods that will not cause disturbances to the unit load. The method for replacing the displacement sensor online is briefly described as follows:
(1) The unit exits the coordinated operation mode. Because in the coordination mode, CCS treats the four high-pressure dampers of the DEH as an implementing agency. Artificially changing the opening degree of a certain high-voltage damper will cause the system to mistakenly believe that the door-opening operation is performed, and then causes the other doors to follow. Causes load fluctuations.
(2) The DEH enters into the power circuit and manually opens the discharge valve of the door (the displacement sensor of the door is faulty). The oil driver of the door is automatically turned off when it loses oil pressure, and the door is not actuated with the servo valve command.
(3) Connect the new sensor to the terminal board of the VCC card. It should be noted that when connecting the cables, follow the sequence of 3-2-1. When the cable is disconnected, remove it in the order of 1-2-3. Otherwise, it will be false. The valve position (opening is shown as maximum), if it does not exit the coordination mode, it will cause great disturbance to the regulating system.
(4) Iron core of man-made movement sensor, analog full-stroke switch of the door (such as high-pressure door adjustment stroke of 4Omm), refer to the servo system debugging chart to adjust the zero and full scale of VCC card to 0~4V.
(5) After the adjustment is completed, the sensor is installed on the regulating door, artificially sends the closing instruction 0% to the adjusting door, and then manually closes the discharge valve of the adjusting door to ensure that the adjusting door will not be suddenly opened; the manual opening command is given to the adjusting door and each time increases At 3%, the door is gradually opened. When the command is added to 50%, the offset of the VCC card is adjusted so that the difference between the APs can meet the requirement.
This method has been successfully applied several times in the six units of our plant, eliminated defects in time, satisfies the unit load adjustment requirements, and ensured the unit's output.
IV. Concluding remarks The above-mentioned typical failures of DEH system displacement sensors are the abnormal conditions that have occurred several times in the six units of Jiaozuo Power Plant in the past few years. After the efforts of technicians at all levels, the fault has been ruled out. It is hoped that the above troubleshooting method can bring some help to everyone.
Displacement Sensor Failure Analysis and Cause Solution
I. INTRODUCTION The original capacity of the Jiaozuo Power Plant was 6×2OOMW. After several years of capacity expansion, the total installed capacity has reached 132OMW. Since October 1999, Jiaozuo Power Plant has used a major overhaul to carry out a complete DEH system transformation of the low-pressure turbine oil speed control system for six steam turbines. The DEH systems of these six machines are all based on the DEH-IIIA system manufactured by Xinhua Control Engineering Co., Ltd. The two high-pressure main valves, two medium-pressure main valves, and eight speed-regulating valves are individually controlled by a high-voltage reactor. Fuel oil motivation control.
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