1. 1 steam turbine 300MW steam turbine electro-hydraulic control system
The 2x steam turbine > 300MW steam turbine of Luoyang shouyangshan Power Plant Phase II is Hitachi TCDF-33.5 subcritical, intermediate reheat, double cylinder and double exhaust, impulse and condensing steam turbine, which was put into operation in 1995, 65438+February and1March 1996. The control system of steam turbine is digital electro-hydraulic control (D-EHG), which adopts low-pressure turbine oil electro-hydraulic control. The setting of the actuator is 1 high-pressure oil motor drives four high-pressure speed regulating valves, and two medium-pressure oil motors drive two medium-pressure speed regulating valves. Each oil motor is controlled by an electro-hydraulic servo valve, and the electro-hydraulic servo valves of three oil motors (CV, left and right ICV) of 1 steam turbine are made in Japan. The control oil and lubricating oil use the same oil source, that is, N32 antirust turbine oil in the main oil tank, and the control oil pipeline is equipped with a precision filter (accuracy is 5 1μm).
1.2 has a problem.
Units 3 and 4 of Shouyang Road Power Plant started trial operation on 1995. During the start of the unit, the oil motor suddenly stopped. After inspection, the control system is normal and the signal transmission is normal, which are all caused by the failure of the servo valve. After replacing the servo valve, the regulating system returned to normal. When the unit runs stably with load and the medium pressure regulating valve is tested for one day, the oil motor will not move, and the oil motor will be fully opened or closed.
All inspections are servo valve failures.
When the servo valve fails, it must be replaced. However, the servo valve in this regulation system design cannot be isolated, so it must be stopped and replaced. Units 3 and 4 of shouyangshan Power Plant were shut down due to servo valves: 8 times and 5 times respectively in 2000 and 1 time and 2 times respectively in 2006; By June 2002, only Unit 3 was shut down for 4 times due to the servo valve. The removed faulty servo valve was inspected, and it was found that the internal filter element was blocked, the nozzle was blocked and the slide valve was stuck. The filter element in the servo valve is blocked, which leads to the low control pressure in the front stage of the servo valve, which can not control the action of the secondary slide valve of the eye valve, resulting in the oil motor refusing to operate (no response to the control signal); The nozzle is blocked and the oil motor is turned off; The servo valve is stuck, which keeps the oil motor in the fully open or fully closed position. Oil pollution is the main cause of the above faults, and the servo valve jamming caused by oil pollution accounts for 85% of the servo valve faults [1].
1.3 Oil quality and measures to prevent servo valve from jamming
Since the servo valves of Units 3 and 4 are often stuck in trial operation, shouyangshan Power Plant attaches great importance to oil quality after it is handed over to production. 1996 set up an oil filter class to strengthen the management of oil filters and improve the cleanliness of oil quality. The frequency of servo valve jamming is much lower than that during trial operation, but the number of times is still relatively high.
Hitachi turbine maintenance manual shows that the servo valve can work normally in oil with pollution level equal to or lower than NASl638. The pipeline of the second-stage oil system is designed as a sleeve type, and the control oil pipe for supplying oil to the servo valve after the filter screen is located in the lubricating oil return pipe, so it is impossible to sample and monitor, and only the cleanliness of lubricating oil can be monitored. According to the old quality standard of turbine oil in power plant [2], the requirement for mechanical impurities in oil is visual inspection without impurities. Since 1996, the lubricating oil of No.3 and No.4 engines has been tested every week, and the oil samples are transparent and free of impurities (containing a small amount of water for some time, and impurities are rarely checked). The new quality standard for turbine oil used in power plants [3] not only requires that there is no mechanical impurity in the oil by visual inspection, but also puts forward higher requirements for the oil quality: the granularity of units of 250MW and above is required to be inspected, and a fuel tank and mineral turbine oil are used for some turbine lubrication systems and speed control systems of 8-9 referring to foreign standard limit NASl638 or 6 referring to MOOG300MW turbine. At this time, the granularity index in engine oil should be in accordance with the index provided by the manufacturer, and the testing period is every 6 months 1 time. 200 1 The turbine oil samples of Units 3 and 4 were analyzed for particle size, and the particle size of running oil was all qualified (see table 1).
The jamming of servo valve causes the shutdown, which has a great influence on the safety of the unit, while the unplanned shutdown of the unit caused by the jamming of servo valve affects the economy of the power plant. Shouyangshan Power Plant has taken the following temporary measures:
(1) Replace the servo valve regularly, and replace it when the unit stops for more than 3 months; (2) Regularly replace the control oil filter and clean it; (3) Improve the cleanliness of the oil when the oil filter runs continuously; (4) Strengthen oil quality inspection.
From the operation point of view, the number of downtime caused by servo valve jamming has decreased. However, the problem has not been fundamentally solved. Therefore, after analysis and research, a series of reform ideas such as "using independent control oil source" and "replacing servo valve without stopping" were put forward, but they were all abandoned because of the large amount of system reform, high reform cost or technical infeasibility. After various analysis and research, the scheme of reforming servo valve and selecting DDV valve with strong anti-pollution performance is put forward.
Second, Abex4 15 electro-hydraulic servo valve
2. 1 working principle
Electro-hydraulic servo valve is a kind of electro-hydraulic conversion element and power amplification element, which converts tiny electrical signals into high-power hydraulic energy output and controls the valve position of speed regulating valve. Its performance has a great influence on the electro-hydraulic regulating system, and it is the core and key of the electro-hydraulic regulating system. The servo valve is a two-stage electro-hydraulic servo valve with jet tube force feedback, which is a four-way valve. Its function is to control the amount of oil in and out of the hydraulic system to make it proportional to the input electrical signal. It is mainly composed of valve body, torque motor (coil and armature), permanent magnet, 1 stage nozzle, pressure feedback spring, secondary slide valve, O-ring and housing (see Figure 65438).
Its working principle: a small amount of hydraulic oil flows from the oil source, passes through the filter screen, then flows through the hose connected to the rotor of the torque motor, and finally flows out from the nozzle. Oil from the nozzle is sprayed onto two oil collecting pipes, which are connected to both ends of the slide valve respectively. When there is no offset, the pressure generated by each oil collector is about half of the pipeline pressure, so there is no pressure difference, so the slide valve is balanced. When the current flows through the torque motor, a certain torque is generated, which makes the rotor of the torque motor rotate by a small angle. If the rotor rotates counterclockwise, the oil injection pipe moves to the right, so that more oil is sprayed on the right oil collector, that is, pressure is generated, while the pressure generated by the left oil collector is smaller. In this way, there is a pressure difference on the slide valve, which makes the slide valve move to the left. The slide valve moves to the left until the reaction force generated by the return spring is equal to the force generated by the torque motor. At this time, the slide valve is in a new equilibrium position. The second stage current is proportional. If the current polarity is opposite, the slide valve moves to the other side.
2.2 Main features
(1) This valve is an electro-hydraulic servo valve with jet tube force feedback and two-stage amplification; (2) Low lag and high resolution; (3) high sensitivity, good linearity and high control precision; (4) N32 antirust turbine oil is used as the main control oil tank, which is the same oil source as lubricating oil, and has high requirements on oil quality and poor anti-pollution ability.
2.3 Main technical specifications
Model of servo valve.
Three. Introduction of DDV servo valve technology
3. 1 working principle
DDV servo valve consists of integrated block electronic circuit, linear motor, valve core and valve sleeve (see Figure 2). Its working principle is that the electric command signal is applied to the integrated block of the spool position controller, the electronic circuit generates pulse width modulation (PWM) current in the linear motor, and the oscillator excites the spool position sensor (LVDT). Comparing the demodulated spool position signal with the command position signal, the spool position controller generates current and outputs it to the torque motor, which drives the spool until the spool moves to the command position. The position of the spool is proportional to the command signal. The actual flow q of the servo valve is a function of the spool position and the pressure drop at the metering edge of the spool.
Permanent magnet linear motor structure. Its working principle: the linear motor is a permanent magnet differential motor, and the permanent magnet provides part of the required magnetic force, and the current required by the linear motor is obviously lower than that required by the proportional electromagnetic coil of the same order of magnitude. Linear motors have a neutral middle value because
As soon as it deviates from the neutral position, it will produce a force and a stroke, which is proportional to the stroke and the current. The self-winding motor must overcome the centering force and external additional force (that is, hydraulic pressure and friction caused by pollution) caused by high stiffness spring. When the linear motor returns to the neutral position, the force of the centering spring is in the same direction as the force generated by the motor, which is equivalent to providing additional driving force for the spool, thus greatly reducing the sensitivity of DDV servo valve to pollution. The linear motor returns to the center with the help of the spring, and no external current is needed. In the case of power failure, cable damage or emergency stop, the servo valve can automatically return to the center without external force.
3.2 Main features
DDV valve is a new type of electro-hydraulic servo valve developed by MOOG Company, which has been mass-produced by MOOGGmbH (Germany). It is a direct-drive servo valve, and the closed-loop control of spool position is realized by integrated circuit. The driving device of the valve core is a permanent magnet linear force motor, and the centering spring keeps the valve core in the middle position. The linear force motor overcomes the centering force of the spring to make the valve core deviate from the middle position to two directions and balance in the new position, which solves the shortage that the proportional electromagnetic coil can only generate force in one direction. The closed-loop control electronic circuit of spool position and the pulse width modulation (PWM) drive electronic circuit are solidified into an integrated block, which is fixed in the servo valve with special connection technology, so that the servo valve can control it without supporting electronic devices.
Compared with "jet tube servo valve" (or "two-stage servo valve with double nozzle force feedback"), DDV valve is characterized by: (1) no hydraulic front stage; (2) replacing torque motor with high-power linear force motor; (3) Advanced integrated block and micro position sensor are used to replace the complicated mechanical feedback devices-force feedback rod and spring tube; (4) Low lag and high resolution; (5) Maintain the basic performance and technical indicators of the two-stage servo valve with pre-stage; (6) The anti-pollution ability of controlling oil quality is greatly improved; (7) Reduce operation and maintenance costs.
3.3 Main technical parameters
Model and parameters of DDV servo valve
Four, technical transformation scheme and equipment installation and debugging
The goal achieved through technical transformation: (1) completely solve the servo valve jamming; (2) The regulation characteristics of the regulation system have not changed; (3) Having
High reliability and safety; (4) The transformation amount is small.
Modification scheme: (1) Change the CV and ICV servo valves of steam turbine into DDV servo valves. (2) Mechanical aspect: Because the two servo valves are different in shape, opening size and installation size, an oil manifold block for connection is installed between the servo valve and the actuator, and an oil inlet filter screen is installed on the manifold block. (3) Thermal engineering: install power supply and signal conversion box, accept the D-EHG control signal (8ma) of HITASS and two 220V AC power supplies (one UPS and one security section), convert the control signal (8ma) into voltage signal (10V) as the control signal of DDV, and convert the AC 220V into DC 24V as the DDV.
The static test shows that the static characteristics of the control system are basically consistent with the test values before transformation, which shows that the adjustment mode and performance of the whole control system have not changed after the servo valve is changed to DDV valve. Static test data before and after modification
In order to check whether the servo valve is safe after being changed to DDV valve, and whether the actuator can be closed in case of power failure, the power failure test was carried out: adding an open signal, the actuator was opened; Pull out the signal connector locally, and the actuator will automatically shut down.
Verb (abbreviation of verb) operation practice and economic analysis
Unit 4 has been started and stopped many times since it was put into operation in September of 200 1 year, and the regulating system is reliable and stable. There was no unexpected shutdown of the unit due to the blockage of the servo valve.
Influence of technical transformation on unit safety and economy. Safety: prevent the servo valve from jamming, greatly improve the safety and reliability of the unit, and greatly reduce the unplanned downtime of the unit; Economy: besides increasing power generation, technical transformation can save about 740 thousand yuan every year. The technical renovation cost is 200,000 yuan for each set and 400,000 yuan for two sets. 1 unit, 1 year can recover the total investment of two units, with remarkable economic benefits.
Conclusion of intransitive verbs
The actual operation shows that the technical transformation lies in that the electro-hydraulic control system and lubricating oil system of steam turbine share the same oil source, which improves the applicability and anti-pollution ability, solves the problem of electro-hydraulic servo valve jamming, greatly reduces the number of unplanned shutdowns of the unit, and has obvious economic benefits. It can be popularized and implemented in the electro-hydraulic control system of Hitachi similar 00MW steam turbines.
At present, the working fluid of electro-hydraulic control system of domestic units adopts phosphate ester fire-resistant oil, but compared with turbine oil, the physical and chemical properties of phosphate ester fire-resistant oil are strict, expensive and complicated to maintain, especially the waste liquid of phosphate ester fire-resistant oil can not be treated at present, and its pollution is equivalent to nuclear pollution, which is harmful to human health. Considering these factors, it is the general trend that the working medium of the electro-hydraulic control system of the unit develops from fire-resistant oil to turbine oil system.
Although the sensitivity of DDV valve to oil pollution is greatly reduced, the decrease of oil cleanliness will reduce the service life of metering edge of servo valve, so strengthening oil chemical supervision cannot be relaxed at all. At the same time, it is suggested that the unit should carry out load rejection test to further test the load rejection characteristics of DDV.