Talking about Steam Turbine Sequence Valve Control

On Steam Turbine Sequence Valve Control (Jiangsu Taicang Environmental Protection Power Generation Company, Taicang 215433, Jiangsu, China) Liu Tiexiang reveals the scientific nature of valve management design for steam turbines and the knowledge points that need to be mastered in debugging and application.

Foreword The turbines of modern large and medium-sized generator sets are controlled by digital electrohydraulic control system (DEH). Each steam inlet valve is controlled by electric signals and driven by high-pressure oil. The management of the steam inlet valve is obviously an important function of the DEH system, especially the sequential valve control management process is more scientific and complex. In the debugging and practical application, the parameter setting of the sequential valve control is also very strict. If the parameters are not properly set, the switching disturbance between the single valve and the sequence valve is too large, and the main operating parameters of the steam turbine are abnormal, which affects the safety of the unit. It can be seen that the parameter tuning of the sequential valve control is an important part of DEH commissioning.

DEH valve management function The new unit generally adopts the single-cycle valve operation mode during the trial run to make the temperature difference between the rotor and the stator smaller. The effect of temperature difference during variable load operation is less, which is beneficial to the initial running of the unit. In addition, single-valve control is also required during the unit startup or peaking mode operation. However, single-valve operation, high-pressure control valve are involved in opening adjustment, and generally high-pressure adjustment door opening is not large, steam through the adjustment valve has a larger throttling loss. The operation of the unit requires minimizing the throttling loss of the regulating valve and improving the efficiency of the steam turbine. Normally, the throttling loss of the valve is minimized when the valve is close to or near maximum flow. In the sequential valve control mode, only one high-pressure regulating valve is used to adjust the opening degree, and the rest of the regulating doors are kept fully open or fully closed, thus reducing the throttling loss and improving the thermal efficiency of the unit.

For the comparison of thermal efficiency curves for sequential valve control and single valve control, the difference between the two can be clearly seen.

In this way, during the operation of the unit, it is necessary to switch between the single valve control mode and the sequence valve control mode for the unit thermal efficiency or other conditions.

This requires a complicated valve management program to complete. Through the valve in thermal power plant thermal control system application.

Door characteristics, accurate calculation of different working conditions, different valve control methods, and different valve opening corresponding to different steam flow, to achieve valve opening adjustment; at the same time achieve a single valve without disturbance of the unit operation Balanced switching with sequential valve control.

3 valve control principle The valve control program receives the control signal is the steam flow, through the program to calculate the steam flow signal into the corresponding valve opening, in the single valve mode, the high-profile door opening is the same, the calculation is relatively simple, In the sequential valve mode, the opening sequence of the valves needs to be determined, and the opening degree of each valve is separately calculated. In the two ways to convert each other also need to carry out the conversion of flow and opening.

3.1 Feed-forward correction of main steam pressure to steam flow The steam flow received by the valve management program is determined according to the rated main steam pressure. When the main steam pressure is not equal to the rated pressure, the same steam flow rate obtained by adjusting the valve opening is not equal to Controlling the required flow causes the load to adjust for dynamic deviations. Of course, deviations can also be eliminated by applying automatic adjustment loops and feedback corrections. However, this feedback correction has a certain delay, and the overshoot is large. If the steam flow signal is corrected according to the current main steam pressure to compensate for the influence of the main steam pressure on the steam flow rate, the corrected flow rate command is used as the valve opening control signal, and it is apparent that more timely and accurate adjustments can be made. The valve management program performs proportional correction of the flow command according to the main steam pressure, that is: where Q is the corrected steam flow demand value; Q0 is the steam flow demand value before correction; PTREF is the main steam pressure rating; PT is the current main steam pressure.

Correction amount “Pressure deviation pressure correction diagram In the calibration software, the insensitivity zone is set. When the PT deviates from the PTREF by a certain value, it is corrected, as shown in the figure.

3.2 Calculation of Valve Characteristics Click China Automation Control Network and obtain the latest information in the industry. 45bookmark3 ~~ The measurement and control valve management program converts the corrected flow into the valve opening command. The flow and the valve opening must have a certain corresponding relationship, which is usually Said valve characteristic curve, in the software generally uses the polyline function to complete the characteristic calculation. It is the valve characteristic curve of the high-profile door of the 135MW steam turbine of Taicang Environmental Protection Power Generation Company. Its fold line function is shown in Table 1. Violet-chart; flow-opening curve (% flow-opening fold line function under low load conditions, flow and valve The opening degree is in a one-to-one correspondence, but as the load increases, the back pressure after the regulating door also rises. The same valve opening flow rate will change due to the influence of back pressure, so the valve management program first corrects the flow according to the load. Corrected the converted flow under low load, which is the flow-flow coefficient curve, and finally converted into the valve opening according to the flow-opening characteristic curve according to the converted flow.

The top-notch flow is the 135 MW quantity coefficient curve of Taicang Environmental Protection Power Generation Company. The break line function is shown in Table 2. The turbine high valve can obtain the opening degree of each valve according to this flow value.

3.4 Valve opening control when the sequence valve is controlled Bookmark6 The flow request value of the control output is corrected by the main steam pressure feed-forward correction and load correction, and then divided equally into each adjusting valve. Each valve is then set according to the set flow ratio and offset factor. Calculated separately, the difference in flow rate ratio and offset factor determines the order in which the valve is opened and the offset to the opening in the single valve mode. In this way, the final valve opening value is calculated according to the flow-opening function based on the proportional and offset calculated flow values.

The valve management program simultaneously calculates the final flow value of each valve in single valve mode and sequence valve mode. When switching from single valve control to sequential valve control, the value of the final flow value of each valve is calculated from the value calculated by the single valve method. The rate is approached by the numerical value calculated by the sequential valve method, and the valve opening is also close to the valve position required by the sequential valve method. The entire switching process is completed when all valve positions have reached the valve position required for their sequential valve mode. It can be imagined that in the conversion process, some valves must be gradually opened, and some valves are gradually closed.

The increased flow and reduced flow at any time during the entire process should be equal, and the total flow remains unchanged. Therefore, the load of the unit during the conversion process will not be affected, but due to the increase in thermal efficiency when the sequence valve is controlled, the electrical power will increase after switching. When switching from sequential valve control to single valve control, the principle is the same, but the process is reversed.

4 Sequence of valve control parameter setting sequence When the valve is controlled, according to the switching sequence of the high-pressure control valve of the steam turbine, the flow command of each control door is separately calculated to determine the final flow value of each high-pressure control valve and then converted into the opening value of each valve. Calculation of the valve opening command includes main steam pressure correction, load correction, proportional offset correction, and flow-opening function correction. It is a schematic diagram of the calculation of the opening degree of the high pressure regulating door for the 135MW steam turbine of Taicang Environmental Protection Company.

Shun | Fortunately, the valve control flow-flow curve (%) Table 2 Flow-flow break line function (%) 3.3 Valve opening calculation for single-valve control bookmark8 Single-valve method for the same valve opening, so control the output flow After the request value is corrected by the main steam pressure feed forward correction and the load is corrected, the flow request signal f output to the set regulator output that is divided equally to each adjustment 4.1 correction function is first subjected to main steam pressure correction and load correction to become f2. In the single valve mode, F2 is directly adjusted by the opening of the flow rate and becomes the opening degree command. In the sequential valve mode, f2 needs to be corrected by the ratio and offset first, and then it is adjusted by the opening degree of the flow rate to become the opening degree command. The main steam pressure correction function (F(X1)) and the load correction function (F(X2)) and the flow-opening correction function (F(X3)) are determined by the unit characteristics. Generally, the data provided by the steam turbine plant is taken directly. However, when the actual operation finds that these function settings are not appropriate and affect the valve adjustment, they should be re-adjusted through experiments.

The proportional and offset corrections only work in the sequence valve mode. The parameters are determined based on the valve design flow and the valve switching sequence. For the 135MW steam turbine of No. 1 of Taicang Environmental Protection Power Generation Company, when the sequence valve is controlled, 1 high-profile door and 2 high-profile doors are opened at the same time, and 3 high-profile doors and 4 high-profile doors are opened in sequence. According to Steam Turbine click on China Automation Control Network to obtain the latest industry news. Kongzhi.net machine factory design, when the main steam pressure correction and load correction after the flow command f2 reached 73.53%, 1 high-profile doors and 2 high-profile doors fully open, that is, f3 should be 100%; when f2 is 0% , 1 high-profile door and 2 high-profile doors are all off, and the color should be 0%. From this, the (K, B) values ​​of 1 high-profile door and 2 high-profile door can be calculated. Calculated as follows: 0%; f2 reached 99.83% 3 high-profile doors open, that is, f3 is 100%. Calculated as follows: 0%; f reached 122.12% when 4 high-profile doors open, that is, f3 is 100%. When the valve is opened sequentially, there may be a non-linear flow command between the flow command and the actual steam flow in a certain flow range. At this time, it is necessary to turn on the next door to correct and make it linear. This is the setting of the valve overlap. The 135MW steam turbine of No. 1 of Taicang Environmental Protection Power Generation Company has designed the overlap between 3 high-profile doors and 1 and 2 high-profile doors. From the above calculations, it can be seen that when the flow command color reaches 71.977%, the 3 high-profile door is started, and the high-profile doors of the 1 and 2 are not fully open at this time, until the f2 reaches 73.53%, the 1 and 2 high-profile doors are fully open. . Thus, there is a 1.553% overlap between the two. It is a schematic diagram of the sequence of the high valve opening of the sequence valve of the No. 1 135MW steam turbine of Taicang Environmental Protection Power Generation Company.

In order to make the switching between the sequence valve control and the single valve control not affect the load and other working conditions, the switching process must be performed smoothly and without disturbance.

So switching is a slow, gradual process. Taicang Environmental Protection Power Generation Company DEH set a bumpless switching function block to be switched between the two in the valve management program, and set the switching speed to achieve the non-interference of switching. The rate setting of the bumpless switching function block is 0.00104/cycle, one of which is 0.25s. It is calculated that the time for completing the switching is 240s. If the switching time needs to be changed, the speed of the bumpless switching function block can be reversed. Set the value. When the 1st order valve of Taicang Environmental Protection Power Generation Company was put into operation for the first time, due to the manufacturer's understanding of the parameters of the disturbance-free switching functional block parameters, its switching rate was interpreted as a dimension of “0~100”, and the actual non-interfering switching function block rate It is a dimension of "0~1" (ie, a percentage). Thus, the rate of the bumpless switching function block is set to 0.104/cycle, resulting in 100 times faster switching time with the required 240 seconds, and the disturbance is too large to complete the switching. After the parameter is modified, that is to meet the 240s switching time.

4.3 Setting of valve fault signal During the switching process, some high-profile doors will inevitably experience high slope areas. At this time, the valve opening instruction changes very fast, and the valve switching speed cannot keep up, resulting in instantaneous comparison of the opening degree command and valve position feedback. Big deviation. In the program, as long as the deviation between the valve opening command and the valve position feedback reaches 5%, the valve fault signal is output and the switching between the sequence valve and the single valve control is terminated. After the valve position deviation parameter that produced the valve fault signal was modified to 20, the switch was completed successfully.

5 Conclusions There are many parameters and function settings involved in the steam turbine valve management program. It must be familiar with its principles and calculation methods to gradually set. In addition, the design parameters and functions provided by the factory are likely to cause large inaccuracy of actual data and design data due to unit installation or other reasons. When debugging, it is necessary to find the deviation in time and correct it. When necessary, reasonable tests must be repeated to calculate reasonable parameters based on test data. In short, the valve management of a steam turbine is a relatively complex and very rigorous process in DEH. It must be extremely scientific and rigorous when commissioning and carefully set.

The scientists visited Guan Qun, a computer network expert in Changzhou, Jiangsu Province. In 1962 graduated from Nanjing Institute of Technology (formerly Southeast University). Professor and headmaster of Southeast University. He once served as vice chairman of the Jiangsu Provincial Association for Science and Technology. Has long been engaged in computer, computer network, computer integrated manufacturing system (CIMS) research and teaching. As the main member, we successfully developed the first transistor integrator in China, and completed the “Automatic Cutting Drawing System” and “Submarine Electronic Track Instrument” based on this machine. In 1976, she began to engage in computer network and communication research and teaching, edited the first computer network textbook in China, solved technical barriers such as network protocol implementation and protocol migration, and successfully developed OSI network and EDI system, which was applied to many network projects. The effect is significant. Took the lead in the development of the "X.25" communications controller, breaking the monopoly of foreign countries and relying on imports. Has won national and provincial awards. In 1998, he was awarded the Second Prize of National Science and Technology Progress for his participation in the "Camp Air Conditioner Plant CIMS Project." He has published more than 80 academic papers and 5 published books. In 1997 he was elected as an academician of the Chinese Academy of Engineering.

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