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In the long-term cooperation with users, we have received some feedback from users, and the phenomenon is rather special. After analyzing with multiple power plants and main engine plants, we have resolved the problems through the self-processing of the power plants and improved the unit operation. The stability and security in the. Now we will discuss such issues with everyone and work together to improve our operational and analytical capabilities.
In the following, we will divide it into three parts: failure phenomenon, analysis and discussion, and solution. Taking the phenomenon that occurred recently in a 200MW generating unit of a power plant as an example to assist. The unit is 200MW of the former Soviet Union and its capacity after modification is 210MW.
One: Fault phenomenon Under normal operating conditions (usually above 70% of flow), the oil motive works stably, but the load will automatically jump upwards or downwards. The amplitude varies from 2MW~6MW, if it is put in DEH If the power loop or the CCS coordinating control is put into operation, the oscillating phenomenon will occur, causing instability in the control. The figure shows that the operating conditions at the time are: TP = 13Mpa, GV4 position is 30%, (the factory because GV3 is faulty, so interchangeable with GV4 open order), the actual load is 202MW, the load fluctuation is about 4MW.
II. Analysis and Discussion From the perspective of servo control loop, the control includes the instruction from the computer to the VCC card for closed-loop control. The control chart is as follows:
Illustration (VCC control diagram)
The valve servo control circuit principle is as follows: 
If the DEH command is stable and the servo valve and LVDT are not faulty, the controlled oil motive is also stable. From the historical data and real-time data, the DEH setpoint, valve output command and oil motive feedback (including The pre-election LVDT1 and LVDT2) were all very stable, and the actual oil motivation was also found to be very stable at the site, but the power would fluctuate up and down at 4MW. Due to CCS investment, the oscillations during the adjustment process can be seen from the figure. After checking the pressure behind the GV4 door, it was found that there was a jump of about 6 Kg/cm2, and the pressure at the speed regulator level also fluctuates synchronously. This phenomenon has similarities with the several power plants that our company had previously dealt with. In summary, we identified the GV4 valve. There is a problem.
Three: To solve the problem Each valve is connected to the control seat and the oil engine through the valve stem during installation. If the control of the oil motor is stable, the control seat is fastened and the corresponding valve is stable, the above problems will not exist. After step-by-step research on this phenomenon in the last two years between the OEM and the company, we believe there is a possibility that the valve head of the valve will change due to the direction of the total force of the valve head under a certain parameter and position. The point valve head is in an unstable state and the valve head jumps within the pre-opening valve range. The general jumping point is about 80% of the effective stroke of the valve. The lower the jitter point, the greater the impact on the load. The valve head bounce causes post-valve pressure and power to jump.
At this point, according to observations and analysis of the main engine plant, the turbines of the relevant power plants, and the experts of our company, it is believed that reducing the stroke of the pre-open valve can improve and solve such problems. Columns such as 125MW unit pre-valve from 7mm to 4mm after the sudden load jump phenomenon is minimal.
Attach the actual curve when the load suddenly jumps for your reference. 
Analysis of sudden load jump caused by valve
Xinhua's high-voltage pure-electricity DEH-IIIA is a digital electric-hydraulic control system for steam turbines. It is an upgraded product of the original DEH-III type and consists of a computer control part and an EH hydraulic actuator. Currently widely used in major domestic and international power plants, the unit capacity involved 600MW to 25MW. Xinhua's DEH is characterized by stable operation, high control precision, friendly man-machine interface, and easy maintenance. At the same time, it is accompanied by the excellent service tenet that the company has consistently advocated, which has been well received by users at home and abroad.