1 Introduction
Turbine governor is one of the two major regulating equipments for hydroelectric units. It not only plays the role of speed regulation, but also undertakes various working conditions conversion and frequency, power, phase angle and other control of hydroelectric generating units and protects the water wheel. The task of the generator set. Turbine governors have gone through three stages of development: mechanical hydraulic governors, electro-hydraulic governors and microcomputer digital hydraulic governors. In recent years, programmable controllers have been introduced into turbine speed control systems, which have strong anti-interference ability and high reliability; simple and convenient programming and operation; modular structure, good versatility, flexibility, and convenient maintenance; It has the advantages of strong control function and driving ability; it has been practically verified.
In this paper, the research on the PLC hydraulic turbine dual adjustment system is proposed, and the programmable controller is used to realize the dual adjustment of the guide vane and the paddle, which improves the coordination accuracy of the guide vane and the vane for different water heads. Practice shows that the dual control system improves the utilization rate of water energy.
2. Turbine regulation system
2.1 Turbine regulation system
The basic task of the turbine speed control system is to change the opening of the guide vanes of the turbine accordingly through the governor when the load of the power system changes and the rotational speed of the unit deviates, so that the rotational speed of the turbine is kept within the specified range, so as to make the generator unit operate. Output power and frequency meet user requirements. The basic tasks of turbine regulation can be divided into speed regulation, active power regulation and water level regulation.
2.2 The principle of turbine regulation
A hydro-generator unit is a unit formed by connecting a hydro-turbine and a generator. The rotating part of the hydro-generator set is a rigid body that rotates around a fixed axis, and its equation can be described by the following equation:
In the formula
——The moment of inertia of the rotating part of the unit (Kg m2)
——Rotation angular velocity (rad/s)
——Turbine torque (N/m), including generator mechanical and electrical losses.
——Generator resistance torque, which refers to the acting torque of the generator stator on the rotor, its direction is opposite to the rotation direction, and represents the generator’s active power output, that is, the size of the load.
When the load changes, the opening of the guide vane remains unchanged, and the unit speed can still be stabilized at a certain value. Because the speed will deviate from the rated value, it is not enough to rely on the self-balancing adjustment ability to maintain the speed. In order to keep the speed of the unit at the original rated value after the load changes, it can be seen from Figure 1 that it is necessary to change the guide vane opening accordingly. When the load decreases, when the resistance torque changes from 1 to 2, the opening of the guide vane will be reduced to 1, and the speed of the unit will be maintained. Therefore, with the change of the load, the opening of the water guiding mechanism is correspondingly changed, so that the speed of the hydro-generator unit is maintained at a predetermined value, or changes according to a predetermined law. This process is the speed adjustment of the hydro-generator unit. , or turbine regulation.
3. PLC hydraulic turbine dual adjustment system
The turbine governor is to control the opening of the water guide vanes to adjust the flow into the runner of the turbine, thereby changing the dynamic torque of the turbine and controlling the frequency of the turbine unit. However, during the operation of the axial-flow rotary paddle turbine, the governor should not only adjust the opening of the guide vanes, but also adjust the angle of the runner blades according to the stroke and water head value of the guide vane follower, so that the guide vane and the vane are connected. Maintain a cooperative relationship between them, that is, a coordination relationship, which can improve the efficiency of the turbine, reduce blade cavitation and vibration of the unit, and enhance the stability of the operation of the turbine.
The hardware of PLC control turbine vane system is mainly composed of two parts, namely PLC controller and hydraulic servo system. First, let’s discuss the hardware structure of the PLC controller.
3.1 PLC controller
PLC controller is mainly composed of input unit, PLC basic unit and output unit. The input unit is composed of A/D module and digital input module, and the output unit is composed of D/A module and digital input module. The PLC controller is equipped with LED digital display for real-time observation of system PID parameters, vane follower position, guide vane follower position and water head value. An analog voltmeter is also provided to monitor the vane follower position in the event of a microcomputer controller failure.
3.2 Hydraulic follow-up system
The hydraulic servo system is an important part of the turbine vane control system. The output signal of the controller is hydraulically amplified to control the movement of the vane follower, thereby adjusting the angle of the runner blades. We adopted the combination of proportional valve control main pressure valve type electro-hydraulic control system and traditional machine-hydraulic control system to form a parallel hydraulic control system of electro-hydraulic proportional valve and machine-hydraulic valve as shown in Figure 2. Hydraulic follow-up system for turbine blades.
Hydraulic follow-up system for turbine blades
When the PLC controller, electro-hydraulic proportional valve and position sensor are all normal, the PLC electro-hydraulic proportional control method is used to adjust the turbine vane system, the position feedback value and control output value are transmitted by electrical signals, and the signals are synthesized by the PLC controller. , processing and decision-making, adjust the valve opening of the main pressure distribution valve through the proportional valve to control the position of the vane follower, and maintain the cooperative relationship between the guide vane, the water head and the vane. The turbine vane system controlled by electro-hydraulic proportional valve has high synergy precision, simple system structure, strong oil pollution resistance, and is convenient to interface with PLC controller to form a microcomputer automatic control system.
Due to the retention of the mechanical linkage mechanism, in the electro-hydraulic proportional control mode, the mechanical linkage mechanism also works synchronously to track the operating status of the system. If the PLC electro-hydraulic proportional control system fails, the switching valve will act immediately, and the mechanical linkage mechanism can basically track the running state of the electro-hydraulic proportional control system. When switching, the system impact is small, and the vane system can smoothly transition to The mechanical association control mode greatly guarantees the reliability of the system operation.
When we designed the hydraulic circuit, we redesigned the valve body of the hydraulic control valve, the matching size of the valve body and the valve sleeve, the connection size of the valve body and the main pressure valve, and the mechanical The size of the connecting rod between the hydraulic valve and the main pressure distribution valve is the same as the original one. Only the valve body of the hydraulic valve needs to be replaced during installation, and no other parts need to be changed. The structure of the entire hydraulic control system is very compact. On the basis of completely retaining the mechanical synergy mechanism, an electro-hydraulic proportional control mechanism is added to facilitate the interface with the PLC controller to realize digital synergy control and improve the coordination accuracy of the turbine vane system. ; And the installation and debugging process of the system is very easy, which shortens the downtime of the hydraulic turbine unit, facilitates the transformation of the hydraulic control system of the hydraulic turbine, and has good practical value. During the actual operation on site, the system is highly appraised by the engineering and technical personnel of the power station, and it is believed that it can be popularized and applied in the hydraulic servo system of the governor of many hydropower stations.
3.3 System software structure and implementation method
In the PLC-controlled turbine vane system, the digital synergy method is used to realize the synergy relationship among guide vanes, water head and vane opening. Compared with the traditional mechanical synergy method, the digital synergy method has the advantages of easy parameter trimming, It has the advantages of convenient debugging and maintenance, and high precision of association. The software structure of the vane control system is mainly composed of the system adjustment function program, the control algorithm program and the diagnosis program. Below we discuss the realization methods of the above three parts of the program respectively. The adjustment function program mainly includes a subroutine of a synergy, a subroutine of starting the vane, a subroutine of stopping the vane and a subroutine of the load shedding of the vane. When the system is working, it first identifies and judges the current operating condition, then starts the software switch, executes the corresponding adjustment function subroutine, and calculates the position given value of the vane follower.
(1) Association subroutine
Through the model test of the turbine unit, a batch of measured points on the joint surface can be obtained. The traditional mechanical joint cam is made based on these measured points, and the digital joint method also uses these measured points to draw a set of joint curves. Selecting the known points on the association curve as nodes, and adopting the method of piecewise linear interpolation of the binary function, the function value of the non-nodes on this line of the association can be obtained.
(2) Vane start-up subroutine
The purpose of studying the start-up law is to shorten the start-up time of the unit, reduce the load of the thrust bearing, and create grid-connected conditions for the generator unit.
(3) Vane stop subroutine
The closing rules of the vanes are as follows: when the controller receives the shutdown command, the vanes and the guide vanes are closed at the same time according to the cooperative relationship to ensure the stability of the unit: when the guide vane opening is less than the no-load opening, the vanes lag When the guide vane is slowly closed, the cooperative relationship between the vane and the guide vane is no longer maintained; when the unit speed drops below 80% of the rated speed, the vane is reopened to the starting angle Φ0, ready for the next start-up Prepare.
(4) Blade load rejection subroutine
Load rejection means that the unit with load is suddenly disconnected from the power grid, making the unit and the water diversion system in a bad operating state, which is directly related to the safety of the power plant and the unit. When the load is shed, the governor is equivalent to a protection device, which makes the guide vanes and vanes close immediately until the unit speed drops to the vicinity of the rated speed. stability. Therefore, in the actual load shedding, the vanes are generally opened to a certain angle. This opening is obtained through the load shedding test of the actual power station. It can ensure that when the unit is shedding load, not only the speed increase is small, but also the unit is relatively stable. .
4 Conclusion
In view of the current technical status of my country’s hydraulic turbine governor industry, this paper refers to the new information in the field of hydraulic turbine speed control at home and abroad, and applies the programmable logic controller (PLC) technology to the speed control of the hydraulic turbine generator set. The program controller (PLC) is the core of the axial-flow paddle-type hydraulic turbine dual-regulation system. The practical application shows that the scheme greatly improves the coordination precision between the guide vane and the vane for different water head conditions, and improves the utilization rate of water energy.
Post time: Feb-11-2022
