Common faults and analysis of displacement sensors

Common faults and analysis of displacement sensors

1. Case 1

In a certain customer case, the pressure regulating valve in Unit # 3 and Unit # 2 repeatedly experienced intermittent small and severe shaking, with a regulating valve command of 110% and no change. The feedback value varied between 86-95mm, and the local regulating valve and EH oil pipeline shook violently. In severe cases, there have been cases where the signal wire connection plug of the displacement sensor fell off due to excessive vibration.

Reason analysis: The displacement sensor of the control valve malfunctioned, causing distortion of the feedback signal; The loosening of the command control line of the servo valve causes the variation of the DEH control command signal received by the servo valve.

Inspection and handling: When checking the command control line of the servo valve, it was found that the wiring was loose, and the shaking phenomenon disappeared after tightening; When checking the displacement sensor, it was found that the feedback wire plug fell off. After reinstalling and tightening, the shaking phenomenon disappeared. Later, it was replaced with an integrated sensor without a plug to avoid such a malfunction.

2. Case 2

In a certain customer case, the high-pressure control valve of Unit # 6 and Unit # 2 repeatedly experienced intermittent and violent shaking. At first, the method of switching between single and multiple valves and adjusting the load in a small amount could avoid valve shaking, but this method is irregular and still cannot completely eliminate this phenomenon. The most severe shaking occurred on February 2, 2001 (when the unit was operating with 18OMW), which caused a significant fluctuation in load between 160 and 2O0MW, with the # 2 high-pressure control valve jumping by 20%; After stabilizing for 15 minutes, there was a series of shaking again, with a significant fluctuation in load between 130 and 19OMW, and the # 2 high-voltage regulating valve jumping between 50 and 100%. During this period, the vibration of axis # 2 increased by 116& Mu; M mutation to 16O& Mu; m. The axial displacement oscillates between -0.1mm and -0.3mm. Throughout the entire process, the # 2 high-voltage control valve command remained at 100%.

Cause analysis: When the # 2 high-voltage control valve shakes, there is a sudden increase in the feedback signal of the # 1 displacement sensor, causing the DEH command value (A value) of the VCC card to be much lower than the feedback value (P value) of the high selected control valve, resulting in the sudden closing of the control valve and a decrease in load. After a sudden drop in load, other high-voltage control valves were opened to maintain the target load under the action of the power circuit, resulting in a sudden increase in load. In addition, the setting of the overlap degree of the high-pressure control valve is relatively large, and the # 1 and # 2 high-pressure control valves are not fully opened at 18OMW, resulting in poor adjustment stability of the control valve and exacerbating the oscillation amplitude of the valve.

Treatment: Increase the frequency difference between two displacement sensors (from 5OHz to 100Hz) to reduce the possibility of resonance between the two sensors; Remove the # 1 displacement sensor and the shaking phenomenon disappears; Change the overlap of the high-voltage regulating valves. When the # 1 and # 2 regulating valves are opened to 75%, the # 3 regulating valve begins to open, and when the # 3 regulating valve is opened to 50%, the # 4 regulating valve begins to open.

3. Case Three

In a customer case, the load of Unit # 2 suddenly changed, and the DEH screen showed that the high-pressure regulating valve of Unit # 2 was fully open, and the pressure after the regulating valve decreased from 12.3NPa to 9.2MPa.

Reason analysis: After analyzing historical data, it can be seen that the LVDTl feedback value suddenly increased at that time, causing the system to believe that the # 2 high-voltage regulating valve was opened too large, and thus issued a closing command. Due to LVDTl being damaged, although the control valve has been closed, the feedback value is still at its maximum and displayed as fully open. It can be seen that the sudden drop in load is caused by LVDTl damage.

Handling: Due to LVDT2 being damaged before this, both sensors have malfunctioned and must be replaced online to ensure normal load control.