Summary:
A 300MW unit of a power plant in Henan Province, from January 3 to March 13, 2008, the abnormal operation of the servo valve of the digital electro-hydraulic control system of the steam turbine caused frequent and unintentional sudden self-closing and self-opening in the operation of the high and medium pressure regulating valves As of July 2008, there were as many as 48 abnormal actions, which seriously affected the safe operation of the unit.
1. Influencing factors of abnormal operation of servo valve
The main features of the abnormal operation of the servo valve of the unit: there is no control system command during each abnormal operation. The abnormal operations are suddenly and quickly closed or slowly closed. After the abnormal operation, they return to normal automatically, and the actions are faster when the valve is resumed; Abnormal movements have occurred when the EH oil pressure is stable or fluctuating. The valve closing and opening curves are continuous and smooth, and there is no local slow increase or pause. Return the partially replaced servo valve to the factory for inspection and maintenance without corrosion or damage. Install the servo valve replaced by the unit in DEH of other units and use it without any abnormality.
In order to find the cause and seek countermeasures, a comprehensive analysis of the factors that may affect the abnormal operation of the servo valve was carried out.
1.1 Electromagnetic interference
If it is a problem of electromagnetic interference, the symptom should be that multiple servo valves act together, and the action frequency is very fast, and the direction is uncertain. At the same time, the power plant confirmed that the grounding condition was normal. Therefore, the electromagnetic interference factor can be excluded.
1.2 Solenoid valve DC power supply
The solenoid valve of the control valve of the unit normally operates in a charged state, and is supplied with 110V DC power from the electric power. There is a main switch (fuse) on the busbar, and a sub-switch (fuse) on each solenoid valve. .
Only one valve operates at a time during abnormal operation of the unit, so the possibility of problems with the main power supply and the main switch can be ruled out; due to the abnormal operation of the unit, sometimes it is faster (2 ~ 3s), sometimes slower (40s ~ 7min), and The instantaneous power failure of the solenoid valve is equivalent to a protective action. The closing speed of the valve should be fast (<0.45), so the possibility of instantaneous power failure of the solenoid valve is also very small. At the same time, the power plant confirms that the main switch (insurance) and sub-switch (insurance) are normal. Therefore, the fault is not caused by DC power supply.
1.3 EH oil pressure fluctuation
From the data recorded by the unit's DCS, it can be seen that when the normal operation load of the unit is stable, the valves are not operated, and the EH oil system does not supply a large amount of oil in a moment, the EH oil pressure is sometimes stable and sometimes fluctuates frequently. The maximum fluctuation range is 10.6 ～ 13.2MPa, EH oil pressure is stable and fluctuates, the servo valve has abnormal operation, so there is no direct correlation between the oil pressure fluctuation and abnormal operation.
1.4 Fuel oil resistance
(1) Foam characteristics When the anti-fuel foam characteristics exceed the standard, more foam may appear in the oil, which affects the stability of the oil pressure, causing fluctuations in the oil pressure and causing the adjustment system to oscillate. The characteristic of the oscillation is continuous and uninterrupted. When the valve of the unit is abnormally operated, the single valve is abnormally closed and opened, and there is no swing phenomenon, so it can be ruled out that the abnormal operation of the valve is caused by the anti-fuel foam characteristics exceeding the standard. After verification, the unit's anti-fuel foam characteristics did not exceed the standard.
(2) Resistivity and acid value The unit's anti-fuel acid value and resistivity exceed the standard and the water content is high, indicating that the oil is contaminated and the oil quality is degraded (Table 1). Deterioration of oil quality will lead to increased sludge, causing particulate matter to exceed standards.
(3) Particulate matter is the most harmful pollutant in the hydraulic system. It not only accelerates the wear of the hydraulic components, but also blocks the gaps and orifices of the components, and causes the control components to malfunction, causing system failure and even being forced to shut down. According to statistics, hydraulic system failures caused by solid pollutants account for 60% to 70% of total pollution failures. Particles in the anti-fuel, especially large particles, can cause the servo valve supply line to become clogged, resulting in unstable oil pressure and abnormal operation of the servo valve. Its characteristics are irregular and discontinuous. The particulate matter in the oil can come from the pollution of external dust, or from the corrosion products of the system or the sludge formed by the deterioration of the oil quality. Refer to Table 2 for the correlation between abnormal operation of servo valve and anti-fuel particle size.
It can be seen from Table 2 that the anti-fuel particle size test results from January to June 2008 were all unqualified, and the highest level reached level â…¡ (NAS1638, the same below), and the frequency of the corresponding servo valve during this period was also high. Due to the large number of units in the plant and the limited number of external oil filters, the daily oil filtering method is to put the bypass regeneration device of the anti-fuel system into operation. The external oil filter is not regularly connected to the system for oil filtering. The filter results of the oil filter of the oil machine improved and the results of particle size detection improved. On July 2, 8 and 21, the test results were 8, 6, and 5, and the frequency of the servo valve during this period also greatly reduced. At the end of July, through the cleaning of the oil system and the oil filtering and regeneration treatment, the particle size was detected to be level 2 on August 6 and 14, respectively, and there was no abnormal movement of the servo valve during this period. Track the servo valve changes from September to November, once a month. Therefore, there is a significant correlation between the frequency of servo valves and the level of anti-fuel particle.
According to the above analysis, it is believed that the anti-fuel particle exceeding the standard is the direct cause of the abnormal operation of the servo valve.
Odm Oem Connectors,Motor Controller Connector,High Speed Crimping Connector,High Speed Optoelectronic Connector
Zooke Connectors Co., Ltd. , http://www.zookeconnector.com